A TREATISE ON DRY ROT IN TIMBER.
CHAPTER I.
ON THE NATURE AND PROPERTIES OF TIMBER.
In considering the subject of Timber trees, we commence with their Elementary Tissues, and first in order is the Formative Fluid, which is the sole cause of production of every tissue found in trees. It is semi-fluid, and semi-transparent, and in this condition is found abundantly between the bark and the wood of all trees in early spring; and thus separates those parts so as to permit the bundles of young wood to pass down from the leaves, and thus enable the tree to grow. It is under these conditions that the woodman strips the bark from trees which are to be cut down, since then it does not adhere to the wood.
The first step in the formation of any tissue from the formative fluid is the production of a solid structureless fabric called Elementary Membrane, and a modification of that fabric termed Elementary Fibre.
The structures which are produced from the above-mentioned “raw material” are very varied in appearance, and are called Cellular Tissues, to signify that they are made up of hollow cells. The spaces between the cells are called Intercellular Spaces, which are of vital importance, as they contain air. Woody fibre constitutes the mass of the stems of our forest trees. Its peculiar characteristic is that of great tenacity, and power of resistance, and for this its structure is admirably adapted: it consists of bundles of very narrow fibres, with tapering extremities, and is so placed from end to end, that the pointed ends overlap each other. Each fibre is very short, and the partitions which result from the apposition of the fibres, end to end, do not interfere with the circulation through them. The tube is not composed of simple thin membranes only; but in addition has a deposit within it, which, without filling the tube, adds very greatly to the strength of the fibre: an arrangement whereby the greatest strength and power of resistance and elasticity shall be obtained; and, at the same time, the functions of circulation uninterruptedly maintained. The strength is mainly due to the shortness of each fibre, the connection by opposite ends of many fibres, almost in one direct line, from the root upwards; and lastly, to the deposit on the inner side of the membrane. The uses of woody fibre are very varied and most important; it is the chief organ of circulation in all wooded plants, and, for this purpose, pervades the plant from the root to the branches. The current in this tissue is directed upwards from the shoot, through the stem to the leaves, and downwards from the leaves through the bark to the root. Thus, its current has a twofold tendency; the ascending and chief one being for the purpose of taking the raw, or what is called the common sap, from the ground to be digested in the leaves, and the descending being devoted to the removal from the leaves of the digested, or what is termed the proper sap, to be applied to the purposes of the tree, and also of the refuse matter to be carried to the roots, and thence thrown out into the soil as a noxious material. The proper sap differs considerably in different trees; it is always less liquid, and contains a much greater proportion of vegetable matter than the common sap. It is very probable that trees of the same kind produce proper sap of different qualities in different climates.
Woody Fibre may be considered the storehouse of the perfected secretions. It is well known that as trees advance in life, the wood assumes a darker colour, and more particularly that lying near to the centre of the stem. This is due to the deposit of the perfected juices in the woody fibre at that point; and where age has matured the tree, it is probable that the woody fibre so employed is no longer fitted for the circulation of the sap; and, also, that the perfected sap, when once deposited, does not again join in the general circulation. The dark colour of the heart of oak, as contrasted with oak of very recent growth, is an illustration of this fact, as is also the deep colour which is met with in ebony and rose-wood. Technically, the inner wood is called the heart-wood, and the outer or younger wood the sap-wood. Of these, the former contains little fluid, and no vegetable life, and, being the least liable to decay, is therefore the most perfect wood; the latter is soft and perishable in its nature, abounding in fermentable elements; thus affording the very food for worms, whose destructive inroads hasten its natural tendency to decay.
The proportion of sap-wood in different trees varies very much. Spanish chestnut has a very small proportion of sap-wood, oak has more, and fir a still larger proportion than oak; but the proportions vary according to the situation and soil, and according to the age at which they have been felled: for instance, the teak tree in Malabar, India, differs from teak in Anamalai, South India. This subject has been very fully treated by Mr. Patrick Williams, in his valuable work on Naval Timber.
Wooded Stems are divided into two great and well-defined classes, according to their internal conformation, viz. such as grow from without (exogenous), and such as enlarge from within (endogenous). The former are more common in cold, and the latter in hot climates.
Exogenous Stems.—On examining a section of a stem of an oak, or any other of our forest trees, we observe the following parts: first, the pith, or its remains in the centre; second, the bark on the outside; third, a mass of wood between the two, broken up into portions by the concentric deposition of the layers, and by a series of lines which pass from the centre to the circumference. Thus, there are always pith, bark, wood, and medullary rays. Each stem has two systems, the cellular or horizontal, and the vascular or longitudinal, and the parts just mentioned must belong to one or other of those systems. Thus, the pith, medullary rays, and bark belong to the horizontal system; and the wood constitutes the longitudinal system.
The Pith occupies the centre of the stem, and remains throughout the period of growth of some trees, as of the elder; or is abstracted after a few years, as in the oak, and almost all large trees. In the latter class of trees, there are some remains of the pith for many years after the process of absorption has commenced, but at length no vestige can be detected, and its position is known only by the central spot around which the wood is placed in circles. In the old age of the tree the pith frequently assumes a colour which it has obtained from the juices which have been deposited. The connections of the pith are extremely important. Firstly, it is in direct connection with every branch, and is the structure which first conveys fluids to, and receives fluids from every new leaf. It thence becomes the main organ of nutriment, and, at the same time, the chief depository of the secretions. Secondly, it is in equally direct and unbroken connection with the bark, through the medium of the medullary rays; and so becomes the centre of all the movements of sap which proceed in the horizontal system.
The mode in which the ultimate disappearance of the pith occurs has been a matter of speculation. That the circulation in the heart-wood ceases after a certain number of years, and that the connection between it and the bark becomes broken, is proved by the fact that numbers of trees may be found in tolerably vigorous growth within the bark, whereas at the heart they are decayed and rotten. It appears clear that it is not converted into wood, and there are facts against the opinion that it is gradually compressed by the wood; but since it is known that in the growth of the tree much compression of the previously formed wood must occur, and since this compression is a likely theory by which to account for the disappearance of the less resisting pith, it is now generally considered to be one of the causes of this occurrence. As a general rule, the pith, so long as it exists, is not mingled with other than cellular structures; but, in certain instances, wooden fibre has been found with it, and, in others, spiral vessels have been detected.
Medullary Sheath.—Immediately surrounding the pith of all exogenous plants, there is a layer of longitudinal tissue, which has received the name of medullary sheath. This sheath has no special walls, but is bounded by the pith on the inner, and the wood on the outer side. It is in this situation that ducts of various kinds and spiral vessels may be found, and in all cases it conveys the longitudinal structure from the root, direct to each leaf. The integrity of this structure is therefore highly necessary to the life of the tree.
Medullary Rays.—These structures come next in order, and, as has been previously intimated, belong to the horizontal cellular system of the stem; they constitute the channel of communication between the bark and the pith, and are composed of a series of walls of single cells resting upon the root, and proceeding to the top of the tree, and radiating from the centre. They lie between the wedge-like blocks of wood, and as they have a lighter colour than the wood, they are evident on an oblique section of any stem, and are called the silver grain. Their colour and number suffice to enable anyone to distinguish various kinds of wood, and greatly increase their beauty. They cannot, of course, exist before the wood is formed, and are therefore not met with in very young trees. They commence to exist with the first deposited layers of wood, and continue to grow outwardly, or nearest to the bark, so long as the wood continues to be deposited. In those woods which possess in abundance the silver grain, another source of ornament exists, viz. a peculiar damask or dappled effect, somewhat similar to that artificially produced on damask linens, moreens, silks, and other fabrics, the patterns on which result from certain masses of the threads on the face of the cloth running lengthways, and other groups crossways. This effect is observable in a remarkable degree in the more central planks of oak, especially in Dutch wainscot.
The Bark.—As the medullary rays terminate in the bark, on their outer side, the consideration of that part next follows. It forms the sheath of the tree, and its more immediate use is that of giving protection to the wood. If bark did not exist, there would be no formative fluid, and without formative fluid there could not be any deposit of woody fibre.
Wood.—We find wood occupying nearly the whole body of the trunk of the tree, and arranged, as a rule, in a very regular manner. On taking up any piece of wood, but more particularly the entire section of a stem, we first notice a series of circles, which increase in diameter and separate by wider intervals as we approach the bark. In this manner the trunk is composed of numerous zones enclosed within each other. Again, in almost all trees, the medullary rays before mentioned may be observed passing in straight lines from the centre to the circumference; and, as the circle of the stem at the bark is much larger than any circle near to the centre, it follows that the medullary rays will be wider apart at the bark than at the pith. On this view of the subject it may be stated that the stem is composed of a series of wedge-shaped blocks, which have their edges meeting at the centre. The combination of these two views gives the correct idea of the arrangement of the wood, viz. a series of wedges, each divided into segments of unequal width by circular lines passing across them. From this description it must not be imagined that these various portions are detached from each other; for although the medullary rays and the circular mode of deposition both tend to a less difficult cleavage of the wood, they yet bind the parts very closely to each other.
The explanation of the occurrence of distinct zones of wood is, that each zone is the produce of one year, and that in our climate, more so than in tropical climates, the period of growth of wood ceases for many months between the seasons, and this induces a distinction in appearance between the last wood of a former, and the first wood of a succeeding year. This distinction is maintained throughout each year, and throughout a long series of years.
The enclosure of zone within zone, is owing to the mode in which the wood is produced, and the position in which it is deposited. Wood is formed by the leaves during the growing season, and passes down towards the root between the bark and the wood of the previous year; and, as the leaves more or less surround the whole stem, the new layer at length completes a zone, and perfectly encloses the wood of all former years. This is the explanation of the term exogenous, which is derived from two words signifying to grow, outwardly, for the stem increases in thickness by successive layers on the outer side of the previously formed wood.
The thickness of the zone for the year is rarely equal around the whole circumference of the stem, and this is due to the lesser abundance of leaves on the branches of one side than on the other, or to the prevalence of winds, or some other physical cause, acting in that direction in opposition to the growing process. It should be observed that there is not in timber any appearance of a gradual change from alburnum to perfect wood. On the contrary, in all cases the division is most decided; one concentric layer being perfect wood, and the next in succession sap-wood.
The age of trees has been inferred, when a section of the whole stem could be examined, by counting the number of rings of wood which have been deposited around the pith. In tropical countries, however, this method cannot be always relied upon.
Woods are variable in quality according to the nature of the climate, and of the soil, as also in a considerable degree to the aspect in which they are situated. Trees grown slowly in open, dry, and exposed situations are more fine and close in their annual rings, and more substantial and durable, than those which are grown in close and shady forests, or rapidly reared in moist or sappy places, the latter being soft and broad in their rings, and very subject to decay; and their pith is not always quite in the centre, for the layers are variable also.
The waggon maker takes care to combine toughness and durability by selecting his wood from trees of second growth, or from trees of first growth that from infancy have stood alone, or far apart. If the soft wood trees have stood alone, and are very large (as is often the case with some of the pines), and most of the branches are near the top, the wood near the base of the trunk is sometimes found to be shaky. This defect is produced by the action of heavy winds on the top of the tree, which wrenches or twists the butt, and thus cleaves apart the fibres of the wood. If the main-top (couronnement, of French writers) of a tree dies while the tree is yet standing, it indicates that water has found its way into the trunk, and that the tree is in a state of decay.
The fir which grows on very dry marl, forms very narrow yearly rings; if on rich or damp marl, they are wide; and when on wet soil, they are again smaller. The common fir on moor soil, has even smaller yearly rings than if on dry sand or marl. From this it is evident that too wet or too dry a soil is not suitable for this tree.
The alder and the willow grow best on wet soil, and thrive but poorly when standing dry.
The weight of wood is of great importance, because its hardness, resistance, and its heating power, as well as other valuable properties, are all more or less depending upon it. In the first place, we must consider that even wood which has been forested very light will become heavy, when put for some time into water, but in such timbers the sap is already given to dissolution. If the fibre were the only substance in the wood, then the specific weight would depend upon the number of pores contained in its body; the pores are, however, filled with a substance such as resin, die, &c. Some years since, when the Indian railways were being formed, the native wood-cutters were so well aware of the above-mentioned fact, that they used to cut down the soft and inferior woods in the forests; soak them in water for a certain time; and then endeavour to pass them to the railway contractors as sound, heavy, and good railway sleepers, and the latter, not being acquainted with the Indian woods, were, at first, often deceived.
The hardest, and heaviest woods come from the hotter climates; the only exception is the pine, which thrives considerably better, and furnishes heavier timber, when it has grown in colder regions, or upon high mountains.
Trees grown on northern slopes furnish lighter timber than if grown on southern or western. The soil has great influence upon the width of the yearly rings, and from this we are able to come to a conclusion in regard to the specific weight. In the fir and larch trees the wood is heaviest when their rings are smallest.
The difference in the strength of timber between the south and the north side is attributable to the grain being closer on the north side, as the sap does not rise in the same proportion as upon the south. In forest-grown wood the difference is almost imperceptible, as the sun cannot act upon the trunk of the tree; in open-grown timber, the difference is really perceptible. It is well known that all woods do not lose strength by being open grown, or, in other words, that the south side is not always weaker than the north; that theory only applies to the coniferæ species. In ash it is the opposite, as the south side is the strongest. In soft-wooded trees, as the acer species, the difference is not perceptible, as the annual rings, and the intervening cellular tissues, are so close akin as to render the wood so compact in its grain that there is no difference in its strength. The coniferæ species, or the pines, are the only classes of woods that are stronger on the north side than on the south: it is well known that the difference originates in the wood being more open in the grain on the south side than on the north.
An influence upon the specific weight is exercised by the resin, and the die, which are contained in the interior of the wood. On level dry ground, or deep sandy soil, we find the fir beautifully red inside; but when we look at it on lias soil, it shows broad yearly rings, and hardly any colour at all. The larch tree, again, in such soil, develops itself well with a rich colour. The cause for these appearances must therefore rest with the chemical condition of the soil, and its effect upon the individuality of the fir: it is probably the nature of the soil that causes the difference of character between Honduras and Spanish mahogany; Honduras being full of black specks, and Spanish of minute white particles, as if it had been rubbed over with chalk. Oaks generally furnish good timber when grown slowly in dry ground, whilst those from wet soil appear comparatively spongy; similar results are obtained with other trees.
Many persons constantly employed on wood are of opinion that it becomes harder if it is worked or barked whilst green.
It is not safe to condemn timber, merely because long cracks are visible on the surface. Such openings are frequently only superficial, and do not penetrate deeply into the wood: in such cases it is very little weakened thereby. It is difficult to obtain timber of large scantling without some defects of this kind, but care should be taken to ascertain if they are of a serious nature.
Trees arrive at an age when their wood becomes ripe, and then they are fit for felling; but as upon the proper method and time for doing this, the prevention of dry rot frequently hinges, a separate chapter is devoted to this part of the subject.
CHAPTER II.
ON THE GRADUAL RISE AND DEVELOPMENT OF DRY ROT.
The opinion generally received has drawn a line of discrimination between the decay accompanied by a vegetable spreading on the surface of the timber, and that which is effected by an animal existing within it, which decay is frequently denominated the worm in timber; but as each is equally entitled to the dreaded appellation, they might more justly be distinguished as the animal and vegetable rot.
The dry rot in timber derives its name from the effect produced, and not from the cause: it is so called in opposition to the wet rot, which is properly denominated, as this exists only in damp situations, and is applied to the decomposition which takes place in timber containing sap, and exposed to moisture: but although the dry rot is usually generated in moisture, in some cases it will flourish independent of extraneous humidity. Dry rot differs from wet rot in this respect, that the former takes place only when the wood is dead, whereas the latter may begin when the tree is standing.
Wet rots are composed of porous fibre running from the rot into the trunk of the tree. This rot is of a brown colour, and has an offensive smell. The evil is often found with white spots, the latter of watery substance: when it has yellow flames, it is very dangerous.
A large quantity of the vegetable kingdom consists of plants differing totally from the flowering plants in general structure, having no flowers and producing no seed properly so called, but propagating by means of minute cellular bodies, called spores. These highly organized vegetables are known to botanists as Cryptogamia. Fungi are plants in which the fructifying organs are so minute, that without the aid of a powerful microscope they cannot be detected. To the naked eye, the fine dust ejected from the plant is the only token of reproduction; this dust, however, is not truly seed, for the word seed supposes the existence of an embryo, and there is no such thing in the reproductive bodies of fungi. The correct terms are spores, when the seeds are not in a case; sporidia when enclosed in cases. The spores or sporidia are placed in or upon the receptacle, which is of very various forms and kinds, but how different soever these may be, it is the essential part of the fungus, and in many cases constitutes the entire plant. That portion of the receptacle in which the reproductive bodies are imbedded is called the hymenium: it is either external, as in the Agaric, where it forms gills; or included, as in the puff-balls. The pileus of fungi is the entire head of the plant, not a mere head covering.
Some naturalists have insisted upon the spontaneous production of fungi, while others maintain that they are produced by seed, which is taken up and supported in the air until a soil proper for its nourishment is presented, on which being deposited it springs up of various appearances according to the principle of the seed, and the nature of the recipient.
It is extremely difficult to give a logical definition of what constitutes a fungus. It is not always easy with a cursory observation under the microscope, to determine whether some appearances are produced by fungi, insects, or organic disease; experience is the safest guide, and until we acquire that we shall occasionally fail.
In the ‘Index Fungorum Britannicorum,’ 2479 species of British fungi are enumerated: any detailed account of the arrangement of this extensive family of plants, or of the character of even its principal sections would be impossible within the limits of this volume; all that can be attempted will be a general description of the fungi causing dry rot.
If dry rot shows itself in a damp closet or pantry, the inside of the china or delf lying there will be coated with a mould, or a fine powder like brick-dust. This excessively fine powder is no other than unaccountable myriads of the reproductive spores or seeds of the fungus; they are red in colour, and are produced on the surface of the fungus in millions. Certain privileged cells on the face of the fungus are furnished each with four minute points at their apex, each four bearing a single brick-red, egg-shaped spore; so that the fruit is spread over the surface of the fungus in groups of fours. To see the form of these spores the highest powers of the microscope are required, and then they can only be viewed as transparent objects. If these excessively minute bodies be allowed to fall on wet flannel, damp blotting-paper, or wet wood, they immediately germinate and proceed to reproduce the parent fungus. The red skin of the spores cracks at both ends, and fine mycelial filaments are sent out: this is the “mould,” spawn, or mycelium from which the new fungus (under favourable conditions of continued moisture) appears.
It matters little where we go: everywhere we are surrounded with life. The air is crowded with birds and insects; the waters are peopled with innumerable forms, and even the rocks are blackened with countless mussels and barnacles. If we pluck a flower, in its bosom we see many a charming insect. If we pick up a fallen leaf, there is probably the trace of an insect larvæ hidden in its tissue. The drop of dew upon this leaf will probably contain its animals, visible under the microscope. The very mould which covers our cheese, our bread, our jam, or our ink, and disfigures our damp walls, is nothing but a collection of plants.
The starting point of life is a single cell-that is to say a microscopic sac filled with liquid and granules, and having within it a nucleus, or smaller sac. From this starting point of a single cell, this is the course taken: the cell divides itself into two, the two become four, the four eight, and so on, till a mass of cells is formed.
The researches of Pasteur show that atmospheric dust is filled with minute germs of various species of animals and plants, ready to develop as soon as they fall into a congenial locality. He concludes that all fermentation is caused by the germination of such infinitesimal spores. That they elude observation does not seem strange, when we consider that some infusoria are only ⅟240000 of an inch in length.
It is ascertained that fungi produce seed which contains the properties of germination; and that vegetable corruption is suited to effect it. When we contemplate the fineness and volatility of the germs, the hypothesis will not appear unreasonable that they are conveyed by the rains into the earth, and are absorbed by vegetables; that with the sap they are disseminated throughout the whole body, and begin to germinate as soon as the vegetable has proceeded to corruption. Whatever, therefore, may be the appearance or situation of the fungus producing the dry rot, or from whatever substance it originates, that substance must be in a corrupt state.
Fungi result from, or are attendant on, vegetable corruption, assisted by an adequate proportion of heat and moisture. The sap, or principle of vegetation, brought into activity, is, according to the ‘Quarterly Review,’ No. 15, the cause of dry rot, in as far as it is favourable to the growth of fungi, as it would seem to be when in a state of fermentation.
Vegetable corruption invariably presupposes fermentation.
Fermentation is a state of vegetable matter, the component parts of which have acquired sufficient force to produce an intestinal motion, by which the earthy saline, the oily and aqueous particles therein contained, exert their several peculiar attractive and repulsive powers, forming new combinations, which at first change, and at length altogether destroy the texture of the substance they formerly composed.
There are two things essential towards creating and supporting the intestinal motion, namely, heat and humidity; for without heat, the air, which is supposed to be the cohesive principle of all bodies, cannot be so rarefied as to resume its elasticity; and without humidity there can be no intestinal motion.
According to Baron Liebig, the decay of wood takes place in the three following modes:—First, oxygen in the atmosphere combines with the hydrogen in the fibre, and the oxygen unites with the portion of carbon of the fibre, and evaporates as carbonic acid: this process is called decomposition. Second, we have to notice the actual decay of wood which takes place when it is brought in contact with rotting substances; and the third process is called putrefaction. This is stated by Liebig to arise from the inner decomposition of the wood in itself: it loses its carbon, forms carbonic acid gas, and the fibre, under the influence of the latter, is changed into white dust.
The fungus occasioning the dry rot is of various appearances, which differ according to the situation in which it exists. In the earth, it is fibrous and perfectly white, ramifying in the form of roots; passing through substances from the external surface, it somewhat differs from that form; here it separates into innumerable small branches.
Mr. McWilliam observes, “If the fungi proceed from the slime in the fissures of the earth, they are generally very ramous, having round fibres shooting in every direction. If they arise from the roots of trees, their first appearance is something like hoar frost; but they soon assume the mushroom shape.”
Hence it appears that we frequently build on spots of ground which contain the fundamental principle of the disease, and thus we are sometimes foiled in our endeavours to destroy the fungus by the admission of air. In this case the disease may be encouraged by the application of air as a remedy. When workmen are employed in buildings which contain dry rot, and when they are working on ground which contains the symptoms of this disease, their health is often affected. A London builder informs us, that a few years since, while building some houses at Hampstead his men were never well: he afterwards ascertained that the ground was affected with rot, and that within one year after the house was erected, all the basement floor was in a state of premature decay. Sir Robert Smirke, architect, remarked in 1835, that he had noticed “there are certain situations in which dry rot prevails remarkably.”
The fungus protruded in a very damp situation is fibrous, of moderate thickness, feels fleshy. From the spot whence it arises it extends equally around, wholly covering the area of a circle. This form would possibly continue in whatever situation it might vegetate, if the air had no motion, and every part of the substance on which it grew were equally supplied with a matter proper to encourage the expansion. The surface of this fungus is pursed, and of various colours, the centre is of a dusky brown, mixed with green, graduated into a red, which degenerates into yellow, and terminates in white.
One of the most formidable of the tribe of fungi is the Merulius lachrymans (often called the Dry Rot) of which the following description is given by Dr. Greville: “Whole plant generally resupinate, soft, tender, at first very light, cottony, and white. When the veins appear, they are of a fine yellow, orange, or reddish brown, forming irregular folds, most frequently so arranged as to have the appearance of pores, but never anything like tubes, and distilling, when perfect, drops of water.” Hence the term lachrymans, from lacrymo, Lat., I weep: the Merulius lachrymans is often dripping with moisture, as if weeping in regret for the havoc it has made. In the genus Merulius, the texture is soft and waxy, and the hymenium is disposed in porous or wavy toothed folds. Berkeley, in his ‘Fungology,’ gives the following description, which is similar to Dr. Greville’s: “Large, fleshy but spongy, moist, ferruginous yellow, arachnoid and velvety beneath; margin tomentose, white; folds ample, porous, and gyroso-dentate.” The Merulius is found in cellars and hollow trees, sometimes several feet in width, and is the main cause of dry rot.
Another formidable fungi, which attacks oak in ships, is the Polyporus hybridus (the dry rot of our oak-built vessels). It is thus described by Berkeley: “White, mycelium thick, forming a dense membrane, or creeping branched strings, hymenium breaking up into areæ, pores long, slender, minute.”
From the slow progress dry rot makes in damp situations, it appears that excessive damps are inimical to the fungus, for its growth is more rapid in proportion as the situation is less damp, until arrived at that certain degree of moisture which is suited both to its production and vegetation. When further extended to dry situations, its effects are considerably more destructive to the timber on which it subsists: here it is very fibrous, and in part covered with a light brown membrane, perfectly soft and smooth. It is often of much greater magnitude, projecting from the timber in a white spongeous excrescence, on the surfaces of which a profuse humidity is frequently observed: at other times, it consists only of a fibrous and thin-coated web irregularly on the surface of the wood. Excrescences of a fungiform appearance are often protruded amidst those already described, and are evidences of a very corrupt matter peculiar to the spots whence they spring. According to the situation and matter in which they are produced, they are dry and tough, or wet, soft, and fleshy, sometimes arising in several fungiforms, each above the other, without any distinction of stem; and when the matter is differently corrupted, it not unfrequently generates the small acrid mushroom.
Mr. McWilliam observes, “The fungi arising from oak timbers are generally in clusters of from three to ten or twelve; while those from fir timber are mostly in single plants: and these will continue to succeed each other until the wood is quite exhausted.”
Damp is not only a cause of decay, but is essential to it; while, on the other hand, absolute wet, especially at a low temperature, prevents it. In ships this has been particularly remarked, for that part of the hold of a ship which is constantly washed by the bilge-water is never affected with dry rot. Neither is that side of the planking of a ship’s bottom which is next the water found in a state of decay, even when the inside is quite rotten, unless the rot has penetrated quite through the inside.
It matters little whether wet is applied to timber before or after the erection of a building. Timber cannot resist the effect of what must arise in either case; viz. heat and moisture, producing putrid fermentation; for instance, in basement stories with damp under them, dry timber is but little better than wet, for if it is dry it will soon be wet; decay will only be delayed so long as the timbers are absorbing sufficient moisture, therefore every situation that admits moisture is the destruction of timber.
In a constancy and equality of temperature timber will endure for ages. Sir Christopher Wren, in his letter to the Bishop of Rochester, inserted in Wadman’s ‘History of Westminster Abbey,’ notices “That Venice and Amsterdam being both founded on wooden piles immersed in water, would fall if the constancy of the situation of those piles in the same element and temperature did not prevent the timber from rotting.” Nothing is more destructive to woodwork than partial leaks, for if it be kept always wet or always dry, its duration is of long continuance. It is recorded that a pile was drawn up sound from a bridge on the Danube, that parted the Austrian and Turkish dominions, which had been under water 1500 years.
The writer of an article on the decay of wood, in the ‘Encyclopædia Britannica,’ 1855, observes, “If a post of wood be driven into the ground, the decay will commence at the surface of the ground; if driven into the earth through water, the decay will commence at the surface of the water; if used as a beam let into a damp wall, rot will commence just where the wood enters the wall.”
Humboldt observes in his ‘Cosmos,’ with reference to damp and damp rooms, that anyone can ascertain whether a room is damp or not, by placing a weighed quantity of fresh lime in an open vessel in the room, and leaving it there for twenty-four hours, carefully closing the windows and doors. At the end of the twenty-four hours the lime should be reweighed, and if the increase exceeds one per cent. of the original weight, it is not safe to live in the room.
Decay of timber will arise from the effects of continued dryness or continued wetness, under certain conditions; or it may also arise from the effect of alternate dryness and moisture, or continued moisture with heat.
At one time dry rot appears to have made great havoc amongst the wooden ships of the British Navy. In the Memoirs of Pepys, who was Secretary to the Admiralty during the reigns of Charles II. and James II., reference is made to a Commission which was appointed to inquire into the state of the navy, and from which it appears that thirty ships, called new ships, “for want of proper care and attention, had toadstools growing in their holds as big as one’s fists, and were in so complete a state of decay, that some of the planks had dropped from their sides.”
In the ‘European Magazine’ for December, 1811, it is stated that, “about 1798, there was, at Woolwich, a ship in so bad a state that the deck sunk with a man’s weight, and the orange and brown coloured fungi were hanging, in the shape of inverted cones, from deck to deck.”
Mr. William Chapman, in his ‘Preservation of Timber from Premature Decay,’ &c., gives several instances of the rapid decay of the ships of the Royal Navy, about the commencement of the present century. He mentions three ships of 74 guns each, decayed in five years; three of 74 guns each, decayed in seven years; and one of 100 guns, decayed in six years. Mr. Pering, also, in his ‘Brief Enquiry into the Causes of Premature Decay,’ &c., says that ships of war are useless in five or six years; and he estimates the average duration to be eight years, and that the cost of the hull alone of a three-decker was nearly 100,000l. Mr. Pering was formerly at the dockyard, Plymouth, and therefore a good authority, if he availed himself of the opportunities of studying the subject. He has stated that he has seen fungi growing so strong betwixt the timbers in a man-of-war, as to force a plank from the ship’s side half an inch.
No doubt a great deal of this decay was attributable to the use of unseasoned timber, and defective ventilation; but there is too much reason to believe that it was principally owing to the introduction of an inferior species of oak (Quercus sessiliflora) into the naval dockyards, where, we imagine, the distinction was not even suspected. The true old English oak (Quercus robur) affords a close-grained, firm, solid timber, rarely subject to rot; the other is more loose and sappy, very liable to rot, and not half so durable.
One cause of the decay of wood in ships is the use of wooden treenails. A treenail is a piece of cleft wood (made round), from 1 foot to 3 feet 6 inches in length and 1½ inch in diameter. As the treenails are also made to drive easy, they never fill the holes they are driven into; consequently, if ever it admits water at the outer end, which, from shrinking, it is liable to do, that water immediately gets into the middle of the plank, and thereby forms a natural vehicle for the conveyance of water. The treenail is also the second thing which decays in a ship, the first, generally, being the oakum. Should any part of the plank or timbers of a ship be in an incipient state of decay, and a treenail come in contact with it, the decay immediately increases, while every treenail shares the same fate, and the natural consequence is, the ship is soon left without a fastening. Treenails in a warm country are sure to shrink and admit water.
Mr. Fincham, formerly Principal Builder in Her Majesty’s dockyard, Chatham, considers that the destruction of timber by the decay commonly known as dry rot, cannot occur unless air, (?) moisture, and heat are all present, and that the entire exclusion of any of the three stays the mischief. By way of experiment, he bored a hole in one of the timbers of an old ship built of oak, whose wood was at the time perfectly sound; the admission of air, the third element, to the central part of the wood (the two others being to a certain degree present) caused the hole to be filled up in the course of twenty-four hours with mouldiness, which very speedily became so compact as to admit of being withdrawn like a stick.
The confinement of timber under most circumstances is attended with the worst consequences, yet a partial ventilation tends to fan the flame of decay.
The admission of air has long been considered the only means of destroying the fungus, but as it has frequently proved ineffectual, it must not be always taken as a certain remedy. If dry air be properly admitted, in a quantity adequate to absorb the moisture, it will necessarily exhaust and destroy the fungus; but care should be taken lest the air should be conveyed into other parts of the building, for, after disengaging itself from the fungus over which it has passed, it carries with it innumerable seeds of the disease, and destroys everything which offers a bar to its progress. Air, in passing through damps, will partake of their humidity; it therefore soon becomes inadequate to the task for which it is designed. Owing to this circumstance, air has been frequently admitted into the affected parts of a building without any ultimate success; too often, instead of injuring the fungus, it has considerably assisted its vegetation, and infected with the disease other parts of the building, which would otherwise probably have remained without injury. The timber, which is in a state of decomposition by an intestinal decay, is little affected by the application of air, as this cannot penetrate the surrounding spongeous rottenness which generally forms the exterior of such timber, and protects the action which the humid particles have acquired in the exterior: as the extent and progress of the disease is therefore necessarily concealed, it is difficult to ascertain correctly the effect produced by the admission of dry air. Under these circumstances of necessity and danger, it will require considerable skill to effect the purpose without increasing the disease, and, as each case has its own peculiar characteristics, it is necessary before one attempts to admit air as a remedy, to previously estimate the destructive consequences which may result from so doing, and ascertain whether it will be injurious or beneficial to the building. The joists of the houses built by our ancestors last almost for ever, because they are in contact with an air which is continually changing. Now, on the contrary, we foolishly enclose them between a ceiling of plaster (always very damp to begin with) and a floor; they frequently decay, and then cause the most serious disasters, of which it is impossible to be forewarned.
Damp, combined with warmth, is as a destroying agent, still more active than simple damp alone—the heat being understood as insufficient to carry off the moisture by evaporation; and the higher the temperature with a corresponding degree of moisture, the more rapid the decay. If the temperature to which wood is exposed, whilst any sap remains in it, is too elevated, the vegetable fluids ferment; the tenacity is diminished, and when the action is carried to its full extent, the wood quickly becomes affected by the dry rot. Exposure to the atmosphere in positions where rain can lodge in quantity, contact with the ground, and application in damp situations deprived of air, will render wood liable to the wet rot; and however well seasoned it may have been previously to being brought within the influence of any of these causes, it will infallibly suffer. Air should therefore have free access to the wood in every direction:
… “for without in the wall of the house he made narrowed rests round about, that the beams should not be fastened in the walls of the house.”—1 Kings vi. 6.
Rondelet says, “The woodwork of the church of St. Paul, outside the city walls, which was destroyed by fire in 1823, was erected as far back as the fifth century.” Although the atmosphere surrounding the framework was often at once warm and damp, yet it was never stagnant. It should be remembered that 500 people in a church during two hours give off fifteen gallons of water into the air, which, if not carried away, saturates everything in the building after it has been breathed over and over again in conjunction with the impurities it contains collected from each individual.
Fever, scrofula, and consumption arise in many instances from defective ventilation.
The signs of decay in timber are, as has been stated, fungi. Some of them now and then are microscopic, and owe their existence to the sporules deposited on the surface; while fermentation, generated by prolonged contact with warm, damp, and stagnant air, is as a soil where seeds sow and nourish themselves.
Mr. McWilliam, in his work on dry rot, states that if the temperature be very low or very high, the effects are the same with respect to the growth of fungi. At 80° dry rot will proceed rapidly, at 90° its progress is more slow; at 100° it is slower still, and from 110° to 120° it will in general be arrested. It will proceed fast at 50°; it may be generated at 40°; its progress will be slow at 36°; and is arrested at 32°, yet it will return if the temperature is raised to 50°.
Dry rot externally first makes its appearance as a mildew, or rather a delicate white vegetation, that looks like such. The next step is a collecting together of the fibres of the vegetation into a more decided form, somewhat like hoar frost; after which it speedily assumes the leathery, compact character of the fungus, forming into leaves, spreading rapidly in all directions, and over all materials, and frequently ascending the walls to a considerable height, the colour variable—white, greyish white, and violet, light or decided brown, &c.
In the section of a piece of wood attacked by dry rot a microscope reveals minute white threads spreading and ramifying throughout its substance; these interlace and become matted together into a white cottony texture, resembling lint, which effuses itself over the surface of the timber; then in the centre of each considerable mass a gelatinous substance forms, which becomes gradually of a yellow, tawny hue, and a wrinkled, sinuated porous consistence, shedding a red powder (the spores) upon a white down; this is the resupinate pileus, the hymenium being upwards, of Merulius lachrymans, in its perfect and matured state. Long before it attains to this, the whole interior of the wood on which it is situated has perished; the sap vessels being gradually filled by the cottony filaments of the fungus; no sooner do these appear externally than examination proves that the apparently solid beam may be crumbled to dust between the fingers; tenacity and weight are annihilated.
Dr. Haller says that seven parts in eight of a fungus in full vegetation are found by analysis to be completely aqueous.
The strength of fungi is proportionate to the strength of the timber the cohesive powers and nutritive juices of which they absorb; and according to the food they receive so they are varied and modified in different ways, and are not always alike. Different stages of corruption produce food of different qualities, and hence many of the different appearances of fungi. One takes the process of corruption up where another leaves it off, and carries it forward and farther forward to positive putrefaction.
The forms which fungi assume are extremely diversified; in some instances we have a distinct stem supporting a cap, and looking somewhat like a parasol; in others the stem is entirely absent, and the cap is attached either by its margin, and is said to be dimidiate, or by its back, or that which is more commonly its upper surface, when it is called resupinate. In some species the form is that of a cup, in others of a goblet, a saucer, an ear, a bird’s nest, a horn, a bunch of coral, a ball, a button, a rosette, a lump of jelly, or a piece of velvet.
Decomposition takes place without fungus where the timber and the situation are always moist, as in a close-boarded kitchen floor, where it is always dry, or very nearly so, and where it is alternately wet and dry, cold and hot. When the decomposition is affected with very little moisture, and no fungus, the admission of air will generally prevent further contamination; but where there is abundance of moisture, rottenness, and fungus, a small quantity of air will hasten the destruction of the building.
In timber which has been only superficially seasoned this disease is produced internally, and has been known to convert the entire substance of a beam, excepting only the external inch or two of thickness to which the seasoning had penetrated, into a fine, white, and threadlike vegetation, uniting in a thick fungous coat at the ends, the semblance being that of a perfectly sound beam. In this internal rot a spongy fungous substance is formed between the fibres. This has often been observed in large girders of yellow fir, which have appeared sound on the outside, but by removing some of the binding joists have been found completely rotten at the heart. An instance of this kind occurred at Kenwood (the seat of the Earl of Mansfield) in 1815. Major Jones, R.E., states that on one occasion he was called upon to report on the state of a building in Malta; that the timbers had every external appearance of being sound, but on being bored with an auger they were found internally in a total state of decay. It is on this account that the practice of sawing and bolting beams is recommended, for when timber is large enough to be laid open in the centre this part is laid open to season; so that when a tree is large enough to be cut through to make two or more beams, decomposition is impeded.
The first symptoms of rottenness in timber are swelling, discoloration, and mouldiness, accompanied with a musty smell; in its greater advance the fibres are found to shrink lengthways and break, presenting many deep fissures across the wood; the fibres crumble readily to a fine snuff-like powder, but retain, when undisturbed, much of their natural appearance.
In whatever way boughs are removed from trees, the effect of their removal is, however, very frequently to produce a rotting of the inner wood, which indicates itself externally by a sudden abnormal swelling of the trunk a little above the root; sometimes the trunk becomes hollow at the part affected, and this particular description of rot will almost invariably be found to exist in those trees whose roots are much exposed. The rot itself is either of a red, black, or white colour in the timber when felled, and when either of the two last-named colours prevail, it will be found that the decay does not extend very far into the tree; but if, on the contrary, the colour of the parts most visibly affected should be decidedly red, the wood should be rejected for any building purposes. Sometimes small brown spots, indicative of a commencement of decay, may be observed near the butt or root end of trees, and though they do not appear to be connected with any serious immediate danger to the durability of the wood, it is advisable to employ the material so affected only in positions where it would not be confined in anything like a close, damp atmosphere.
Great hesitation may be admitted as to the use of timber which presents large bands of what are supposed to be indefinitely-marked annual growth, because the existence of zones of wood so affected may be considered to indicate that the tree was not in a healthy state when they were formed, and that the wood then secreted lacked some of the elements required for its durability, upon being subsequently exposed to the ordinary causes of decay.
In many cases when timber trees are cut down and converted for use, it is found that at the junction of some of the minor branches with the main stem, the roots, as it were, of the branches traverse the surface wood in the form of knots, and that they often assume a commencement of decay, which in the course of time will extend to the wood around them. This decay seems to have arisen in the majority of cases from the sudden disruption of the branch close to its roots, with an irregular fracture, and with such depressions below the surface as to allow the sap to accumulate, or atmospheric moisture to lodge in them. A decomposition of the sap takes place—in fact, a wound is made in the tree-and what are called “druxy knots” are thus formed, which have a contagious action on the healthy wood near them.
There is this particular danger about the dry rot; viz. that the germs of the fungi producing it are carried easily, and in all directions, in a building wherein it once displays itself, without necessity for actual contact between the affected or the sound wood; whereas the communication of the disease resulting from the putrefactive fermentation, or the wet rot, only takes place by actual contact.
Timber Beams,—rotten at the heart.
Before dry rot has time to destroy the principal timbers in a building, it penetrates behind the skirtings, dadoes, and wainscotings, drawing in the edges of the boards, and splitting them both horizontally and vertically. When the fungus is taken off, they exhibit an appearance similar both in back and front to wood which has been charred; a light pressure with the hand will break them asunder, even though affected with the rot but a short time; and in taking down the wainscot, the fibrous and thin-coated fungus will generally be seen closely attached to the decayed wood. In timber of moderate length the fungus becomes larger and more destructive, in consequence of the matter congenial to its growth affording a more plentiful supply.
It is a great characteristic of fungi in general that they are very rapid in growth, and rapid in decay. In a night a puff-ball will grow prodigiously, and in the same short period a mass of paste may be covered with mould. In a few hours a gelatinous mass of Reticularia will pass into a bladder of dust, or a Coprinus will be dripping into decay. Many instances have been recorded of the rapidity of growth in fungi; it may also be accepted as an axiom that they are in many instances equally as rapid in decay.
In considering the liability of any particular description of foreign timber to take the dry rot, attention must be paid to the circumstances under which it is imported. Sometimes the timber is a long while coming here, whilst at other times it is imported in a very short period. The length of time consumed in the voyage has a great deal to do with its likelihood of taking the rot: it may have a very favourable passage, or a very wet one, and the ship is frequently, in some degree, affected with the disease. It perhaps begins in the ship, and it may often be seen between the timber or deals, when it will impregnate the wood to a great depth. Whether it is inherent in the timber or not, of this we may be certain, that where there is a fetid atmosphere it is sure to grow. Canadian yellow wood pine timber is more subject to rot than Baltic or Canadian red wood timber, although the latter will sometimes decay in four or five years. Turpentine is a preventive against dry rot, and Canadian timber is sometimes largely impregnated with it, especially the red wood timber; the yellow wood is very subject to dry rot. Very few cargoes of timber in the log arrive from Canada in which in one part or other of nearly every log you will not see a beginning of the vegetation of the rot. Sometimes it will show itself only by a few reddish, discoloured spots, which, when scratched by the finger nail to the extent of each spot, it will be seen that the texture of the timber to some little depth is destroyed, and will be reduced to powder; and on these spots a white fibre may generally be seen growing. If the timber has been shipped in a dry condition, and the voyage has been a short one, there may be a few logs without a spot; but generally speaking very few cargoes arrive from Canada in which there are many logs of timber not affected. But if the cargo has been shipped in a wet condition, and the voyage has been a long one, then a white fibre will be seen growing over nearly every part of the surface of every log; and in cargoes that have been so shipped, all the logs of yellow pine, red pine, and of oak, are generally more or less affected on the surface.
Nearly every deal of yellow pine that has been shipped in Canada in a wet state, when it arrives here is also covered over with a network of little white fibres, which are the dry rot in its incipient state. There is no cargo, even that which is shipped in tolerably dry condition, in which, upon its arriving here, may not be found some deals, with the fungus beginning to vegetate on their surface. If they are deals that have been floated down the rivers of America or Canada, and shipped in a wet state, on their arrival here they are so covered with this network of the fungus, that force is often necessary to separate one deal from another, so strongly does the fungus occasion them to adhere. They grow together again, as it were, after quitting the ship, while lying in the barges, before being landed. Accordingly, if a cargo has arrived in a wet condition, or late in the year, or if the rain falls on the deals before they are landed, and they are then piled in the way in which Norwegian and Swedish deals are piled, that is, flatways, in six months time, or even less, the whole pile of deals become deeply affected with rot; so that, whenever a flat surface of one deal is upon the flat surface of another, the rot penetrates to the depth of ⅛ of an inch. Its progress is then arrested by repiling the deals during very dry weather, and by sweeping the surface of each deal before it is repiled: but the best way is to pile the deals in the first instance upon their edges; by which means the air circulates freely around them, the growth of the fungus is arrested, and the necessity of repiling them prevented. If the ship is built of good, sound, and well-seasoned oak, the rot would perhaps not affect it, but in order to prevent its doing so, the precaution is usually taken to scrape the surface as soon as the hold is clear of the cargo of timber. Were the cargo not cleared, and the hold not ventilated, a ship that was permanently exposed to this fungus would, no doubt, be affected. It is easy, however, to prevent its extending by washing the hold with any desiccating solution.
Anyone who wishes to know how timber is occasionally shipped to this country should read the report of a trial, in the ‘Times,’ 22nd Feb., 1875 (Harrison v. Willis), relative to a cargo of pitch pine shipped from Sapelo, in the Isthmus of Darien, for Liverpool. This cargo, however, never arrived at Liverpool: it was lost at sea.
The motto of the Worshipful Company of Shipwrights is, “Within the ark, safe for ever.” We suggest it should be altered to, “Within the ark which is free from dry rot, safe for ever.”
There are two descriptions of European deals very liable to take the dry rot; viz. yellow Petersburgh deals, and yellow and white battens, from Dram, in Norway. When Dram battens, which have been lying a long time in bond in this country, have not been repiled in time, they have been found as much affected with the dry rot as many Canadian deals; though this has not happened in so short a time as has been sufficient to rot Canadian deals. The fungus growing on the Petersburgh deals and Dram battens has all the characteristics and effects of dry rot as exhibited in the Canadian deals, the detection of dry rot being in most cases the same.
It should be remembered that white deal absorbs more water than yellow; and yellow more water than red; and the quantity of water absorbed by the white accounts for its more rapid decay in external situations; as the greater the quantity of water absorbed the quicker is the timber destroyed. Mr. John Lingard, in his work on timber (1842), states that he has proved that 4½ oz. of water can be driven off from a small piece of fir, weighing only 10 oz. when wet, which is nearly half. This timber was on a saw-pit, and going to be put into a building.
The most general, and the most fatal cause of decay, viz. the wet rot, has attracted less attention than the more startling, but less common evils, the dry rot, and the destruction by insects.
Sir Thomas Deane, in 1849, related before the Institution of Civil Engineers of Ireland, an extraordinary instance of the rapid decay of timber from rot, which occurred in the church of the Holy Trinity at Cork.
On opening the floors under the pews, a most extraordinary appearance presented itself. There were flat fungi of immense size and thickness, some so large as almost to occupy a space equal to the size of a pew, and from 1 to 3 inches thick. In other places fungi appeared, growing with the ordinary dry rot, some of an unusual shape, in form like a convolvulus, with stems of from a quarter to half an inch in diameter. When first exposed, the whole was of a beautiful buff colour, and emitted the usual smell of the dry-rot fungus.
During a great part of the time occupied in the repairs of the church, the weather was very rainy. The arches of the vaults having been turned before the roof was slated, the rain water saturated the partly decayed oak beams. The flooring and joists, composed of fresh timber, were laid on the vaulting before it was dry, coming in contact at the same time with the old oak timber, which was abundantly supplied with the seeds of decay, stimulated by moisture, the bad atmosphere of an ill-contrived burial-place, and afterwards by heat from the stoves constantly in use. All these circumstances account satisfactorily for the extraordinary and rapid growth of the fungi.
Many instances might be mentioned of English oak being affected with dry rot, under particular circumstances. There was a great deal at the Duke of Devonshire’s, at Chiswick, about 60 years ago. Needy builders, who work for contract, sometimes use American oak, and call it wainscot: it is a bad substitute for wainscot, being very liable to warp and to be affected with dry rot. “I know of one public building,” observed the late Mr. Henry Warburton, M.P., “in which it has been introduced, and, I suppose, paid for under that name.”
Another serious instance of the decay of timber from rot occurred some time since in Old St. Pancras Church, London. When the dry rot made its appearance, it spread with amazing rapidity. Sometimes in the course of a night, a fungus of about the consistence of newly-fallen snow, and of a yellowish-white unwholesome colour, would be found to have spread over a considerable surface. The fungus was without shape, but in some cases it rose to a height of 2, 3, or 4 inches above the planks or other surfaces on which it grew. It could be cut with a knife, leaving a clear edge on each side, and there did not seem to be any covering or membrane over the outer or under surface. The smell of those matters was unpleasant, and seemed like the concentration of the smell which had pervaded the church for so long a time before; and, in a short time, beams, planks of flooring, railings, &c., were reduced to rottenness: the colour changed, and a heavy dark-brown dust fell, and represented the once solid timber. On making an examination with a view of discovering the cause of the attack, it was found that in the graveyard, near the church, there were graves, and several vaults: there were also vaults in the inside of the church. Most of them were filled, or nearly so, with water, which had run from the overcrowded graves.
In the interior there were water-logged vaults, and the walls were saturated with damp. It was also seen that from want of proper spouts and drains, near the outer walls, the drip from the large pent roof had fallen into the foundations. In this situation, when the window frames were properly arranged, a drain dug round and from parts of the church, and other alterations, which should long before have been made, were completed, the dry rot vanished, and no more complaints of the foulness of the air have since been heard.
We could quote many cases of rot which have been caused from the want of proper drains and spouts. Architects should remember that the feet of Gothic collar roofs have to bear the whole weight of the roof, and unless well seasoned, and carefully protected from damp, leaks, &c., premature decay and dry rot will be sure to occur. It is surprising what injury leaks from gutters will sometimes do. In 1851, Professor T. L. Donaldson stated that “a brestsummer of American timber was used some time since at a house in London: after an expiration of three years cracks began to appear in the front wall. A friend of mine, an architect, was called in to find out the cause; and after examining different parts of the house, was almost giving up his search in despair, when he thought he would have the shop cornice removed and look at the brestsummer. He then discovered that some water had been admitted by accident, and penetrating the brestsummer, had caused it to rot, and crack the wall.”
Dry rot was found in the great dome of the Bank of England, London, as originally built by Sir Robert Taylor: it also existed in the Society of Arts building, in the Adelphi, London. It was also found in the domes of the Panthéon, and Halle-au-Blé, Paris; but we hope there is no dry rot in the dome of St. Paul’s Cathedral, London, which is constructed entirely of timber, covered externally with lead.
The decayed state of a barn floor attacked by rot is thus described by Mr. B. Johnson: “An oak barn floor which had been laid twelve years began to shake upon the joists, and on examination was found to be quite rotten in various parts. The planks, 2½ inches in thickness, were nearly eaten through, except the outsides, which were glossy, and apparently without blemish. The rotten wood was partly in the state of an impalpable powder, of a snuff colour; other parts were black, and the rest clearly fungus. No earth was near the wood.” This oak was probably of the Quercus sessiliflora species; and there was no ventilation to the floor.
Mr. John Armstrong, carpenter, employed for many years at Windsor Castle, observed: “I was employed a few years back at a house where I found a floor rotten. We took it up; it was yellow pine; it was laid in the damp, but on sleepers, and the sleepers were not rotten: they were of a different description of wood.” Probably the sleepers were of Baltic red wood.
Dr. Carpenter relates an instance of the expansive power resulting from the rapid growth of the soft cellular tissue of fungi. About the commencement of this century the town of Basingstoke was paved; and not many months afterwards the pavement was observed to exhibit an unevenness which could not easily be accounted for. In a short time after, the mystery was explained, for some of the heaviest stones were completely lifted out of their beds by the growth of large toadstools beneath them. One of these stones measured 22 inches by 21 inches, and weighed 83 lb., and the resistance afforded by the mortar which held it in its place would probably be even a greater obstacle than the weight. A similar incident came under the notice of Mr. M. C. Cooke (the author of ‘British Fungi’), of a large kitchen hearthstone which was forced up from its bed by an under-growing fungus, and had to be relaid two or three times, until at last it reposed in peace, the old bed having been removed to the depth of 6 inches, and a new foundation laid. A circumstance recorded by Sir Joseph Banks is still more extraordinary, of a cask of wine which, having been confined for three years in a cellar, was, at the termination of that period, found to have leaked from the cask, and vegetated in the form of immense fungi, which had filled the cellar, and borne upwards the empty wine cask.
Timber decay in contact with stone is a subject deserving consideration. This decay is entirely obviated by inserting the wood in an iron shoe, or by placing a thin piece of iron between the wood and the stone. It is said that a hard crust is formed on the timber in contact with the iron, which seems effectually to preserve it; it is, of course, necessary that a free circulation of air round the ends of the timber be provided. The most notable instance of timber decay in contact with stone with which we are acquainted occurred at the coronation of George IV. Westminster Hall was then fitted up, and they began by laying sleepers of yellow pine. The coronation was suspended for twelve months, and when the sleepers were taken up from the floor of Westminster Hall, they were in a rotten state.
Timber in contact with brickwork is in Suffolk and in some parts of England covered with sheet lead to preserve it from the effects of the damp mortar. Fungi will arise in mortar, if made with road-drift, and water from stagnant ponds, &c., and it may be traced through the mortar joints, and will thus appear on both sides of a wall. Mortar composed of unwashed sand will generate fungi; sea sand, even if washed, should never be used. It is considered that the system of grouting contributes to the early decay of timber; wood bond timber for walls has been consequently replaced by hoop iron bond. In Manchester wood bond is frequently used, and is said to answer well, but the high temperature of the buildings may be a preventive against the decay of timber, as the walls are soon dried. The practice is a bad one.
When timber used as posts inserted in the ground is placed in the inverted position to that in which it stood when growing, it is said to be very much more durable than if placed in its natural or growing position. This is easily accounted for in the valves of the sap vessels of the growing timber opening upwards; but when that position is inverted, the valves of the sap vessels become reversed in their action; and, therefore, when timber is used as posts inserted in the ground, the valves being so reversed prevent the ascent of moisture from the soil in the wood. Mr. W. Howe relates an experiment made to test the comparative durability of posts set as they grew. He says, “Sixteen years ago I set six pairs of bar posts all split out of the butt end of the same white oak log. One pair I set butts down; another pair, one butt down, the other top down; the others top down. Four years ago those set butt down were all rotted off, and had to be replaced by new ones. This summer I had occasion to reset those that were set top down: I found them all sound enough to reset. My experiments have convinced me that the best way is to set them tops down.” Other instances might be given in favour of placing posts in an inverted position in the ground. Posts will sometimes decay, for the following reason: The ends are often sawn off with a coarse implement and left spongy, with the longitudinal fibres shaken or broken a considerable way within the extremity of the wood. In this state the ends of the posts must be apt to absorb from the ground the moisture, which, being retained, and speedily pervading the whole internal surface, especially if painted, appears to cause decay.
With respect to the preservation of wooden fences, Mr. Cruikshank, of Marcassie, gives in detail various experiments from which it appears that—1st. When larch or pine wood is to be exposed to the weather, or to be put in the ground, no bark should be left on. 2nd. When posts are to be put in the ground, no earth should be put round them, but stones. 3rd. When a wooden fence is to be put up, a No. 4 or No. 5 wire should be stretched in place of, or alongside the upper rail.
Mr. G. S. Hartig, in the ‘Revue Horticole,’ gives the results of experiments made with great care and patience, upon woods buried in the earth. Pieces of wood of various kinds 3⅛th inches square, were buried about one inch below the surface of the ground, and they decayed in the following order: the lime, American birch, alder, and the trembling-leaved poplar, in three years; the common willow, horse-chestnut, and plane, in four years; the maple, red beech, and common birch, in five years; the elm, ash, hornbeam, and Lombardy poplar, in six years; the oak, Scotch fir, Weymouth pine, and silver fir, were only decayed to the depth of half an inch in seven years; the larch, common juniper, red cedar, and arbor vitæ, at the end of the last-mentioned period remained uninjured. The duration of their respective woods greatly depends on their age and quality; specimens from young trees decaying much quicker than those from sound old trees; and, when well seasoned, they, of course, last much longer than when buried in an unseasoned state. In experiments with the woods cut into thin boards, decay proceeded in the following order: the plane, horse-chestnut, poplar, American birch, red beech, hornbeam, alder, ash, maple, silver fir, Scotch fir, elm, Weymouth pine, larch, locust oak.
Before quitting the subject of decay of timber when buried in the earth, it will not be out of place to allude to the decay of railway sleepers, taking for example those in India: English and American sleepers will be dealt with more in detail hereafter.
Dr. Cleghorn, Conservator of Forests, Madras Presidency, India, considers the decay of sleepers to arise in a great measure from the inferior description of wood used. Mr. Bryce McMaster, Resident Engineer, Salem, considers that the native wood sleepers in India have hitherto been found for the most part to fail on the Madras Railway, between 30 and 40 per cent. requiring to be renewed annually. Mr. McMaster undertook an investigation with a view of ascertaining the causes of this deterioration, and whether those causes could be overcome so as to render available the vast resources of India. Thirteen hundred sleepers of sixteen different woods were submitted to careful examination and scrutiny twice at an interval of one year. The sleepers were variously placed, both on embankments and in cuttings; in some cases they were entirely covered with ballast to a depth of 4 inches; while in others they were as much as possible uncovered, and completely so from the rails to the ends—the ballast being only raised 2 inches in the middle of the way, and sloped off so as to carry away the water under the rails. From these observations it appeared that only five woods, Chella wungé, Kara mardá, Palai, Karúvalem, and Ilupé, were sound at the end of two years, the other eleven not lasting even that time. Also, that when the sleepers were uncovered, decay was less rapid than when they were buried in the ballast. The plan of leaving the sleepers partially uncovered had many advantages; it effected a saving of the ballast, allowed the defects to be more quickly detected, and kept the sleepers drier. It had been urged that the heat of the sun would split the sleepers and cause the keys and treenails to shrink; but from experience it was found that while among the “uncovered” sleepers there was a large proportion “beginning to split,” or “useless from being split,” there was on the other hand, among the “covered” sleepers, a still larger proportion “beginning to rot,” or “useless from being rotten.” It was also noticed that of the sleepers “beginning to rot,” 19 per cent. had commenced under one or both chairs. This was due to the retention of moisture under them, and might be remedied by tarring the seats of the chairs. As regarded the treenails where the sleepers were rotten, the treenails were invariably found to be in the same state; while, when the heads were exposed to the sun, they were not loosened by shrinking. Another objection was, that the road would be more likely to buckle and twist, but this was not found in practice to be the case. Treenails made in India cost 2l. 10s. to 4l. per 1000, and the woods generally used for the purpose are Vengé, Kara mardá, Erul, Porasa, or satin wood, and Trincomalee. The three woods first named are also extensively employed for keys, but teak keys seem to be the best, and their cost does not exceed 6l. per 1000. From the experience of the Indian engineers it appears that Teak, Saul, Sisso, Pedowk, Kara mardá, Acha, Vengé, Chella wungé, Palai, Erul, Karúvalem, will make very good sleepers to be used plain.
The sleepers which have failed on the Madras Railway might well be divided into two classes,—those which were originally of perishable woods, and were therefore unfit for the purpose; and those which although of good wood had been cut from young trees, and not been allowed to stand until old enough. The first arose from want of experience of the nature of Indian woods: the second from the absence of a proper system of working the jungles.
The wooden sleepers on the Indian railways should be tarred under the seats of the chairs, be laid in dry ballast, and raised slightly in the middle, and sloped off so as to throw the water under the rails. About two-thirds of the Indian woods are practically useless owing to the want of proper artificial means for preserving those of a perishable nature.
The subject of the decay of wood in India and tropical climates is too extensive to be further considered here; but is of sufficient importance to demand a volume to itself; the renewal of decayed wooden sleepers to railways forming annually a most important item in foreign railway budgets.
We have heard that some of our fortifications which have been erected within the last few years to protect our English coast from invasion, have already been invaded by dry rot. If this be true, some one well acquainted with the subject should at once be appointed to find out the cause, and recommend the remedy in each case.
Professional men, if they wish their works to “live for ever,” should consider the after consequences of neglecting to provide against dry rot. If the fungi could speak from under floors, ceiled-up roofs, behind wainscots, girders, &c., we should often hear them exclaim, “A nice moist piece of wood! Surely this belongs to us.” On the beams of a building at Crawley, a carpenter many years ago cut a few words; they are full of meaning in connection with our subject, and they run as follows:
“Man of weal, beware; beware before of what cometh behind.”
CHAPTER III.
FELLING TIMBER.
The end to be attained in the management of timber trees is to produce from a given number the largest possible amount of sound and durable woods. When a tree, under conditions favourable to its growth, ceases increasing the diameter of its trunk, and loses its foliage earlier in the autumn than it is wont to do, and when the top of the tree brings forth no leaves in spring, these facts may be considered as indications of decline, and that the tree is of sufficient age to be felled. The state of the upper branches of a tree may be considered to be amongst the best indications of its soundness, and provided they be in a healthy condition, the withering of the lower branches is a matter of comparatively small importance.
Trees may be considered as tall, middle rank, and low, and the size to which they will attain depends on many different circumstances. Some trees, the stems of which are short on the average, as the lime, are virtually of tall growth, from the manner in which a number of vertical branches of large size ascend from the stem. And other trees, again, whose branches are comparatively short, are of tall growth, in consequence of the length of the stems—like the beech.
The average duration of trees differs, as is well known, in different species, and they exhibit different symptoms of decay. There are oaks in Windsor Great Park, certainly nearly one thousand years old, and which exhibit even now no appearance of approaching the end of their life. Mr. Menzies, the surveyor, in his work on Windsor Great Park, describes some of the indications of incipient decay which are peculiar to the several kinds of trees. “When a beech begins to fail,” he says, “fungi appear either at the roots or on the forks, the leaves curl up as if they had been scorched, and the tree quickly perishes. In an elm, a great limb first fails, while the rest of the tree continues green and vigorous, but in a few years the whole tree suddenly dies. Coniferous trees die gradually, but quickly. The oak shows the first symptoms at the points of its highest branches, while the rest of the tree will remain healthy and sound for years.” This peculiarity of the oak did not escape the eye of Shakespere, that universal observer, who describes the monarch of the woods as not only having its boughs mossed with age, but its
“High top bald with dry antiquity.”
The age for felling trees is a subject which calls for the deepest consideration, but does not always receive that attention which is due to its importance. Timber growers in their haste to supply the market, too often fell trees that have not arrived at maturity, the heart-wood being therefore imperfect, with much sap-wood, and, of course, little durability; but unfortunately they are the more readily led to do so on account of the increase in size being very slow after a certain age. Builders are sensible of the inferior quality of young timber in respect to duration, and it is their province to check this growing evil, by giving a better price for timber that has acquired a proper degree of density and hardness; but, unfortunately, this is an age for cheap building, without much regard being given as to durability.
Felling should not be too early, for the reasons above mentioned; neither should it be in the decline of the tree, when its elasticity and vigour are lost, and the wood becomes brittle, tainted, and discoloured, with the pith gone, and the heart in progress of decay. Maturity is the period when the sap-wood bears a small proportion, and the heart-wood has become uniform and compact. Sir John Evelyn writes, “It should be in the vigour and perfection of trees, that a felling should be celebrated.” It must be obvious, however, that it is a worse fault to fell wood before it has acquired thorough firmness, than when it is just in the wane, and its heart may exhibit but the first symptoms of decay; for in the former there is no perfect enduring timber to be got, while in the latter the greater part is in the zenith of its strength.
Although there are certain symptoms by which it may be ascertained when a tree is on the decline, it is somewhat difficult to decide just when a tree is at maturity. From the investigations of naturalists, however, it may be safe to consider that hard-wood trees, as oak and chestnut, should never be cut before they are sixty years old, the average age for felling being from eighty to ninety years, and the average quantity of timber produced by a tree of that age is about a load and a half, or about 75 cubic feet.
Daviller states (see ‘Cours d’Architecture’) “that an oak should not be felled at a less age than sixty years.” Belidor considers (see ‘Sciences des Ingénieurs’) “that one hundred years is the best age for the oak to be felled.”
It should be remembered that the times mentioned are by no means arbitrary, for situation, soil, &c., have much to do with it. For the soft woods, as the Norway spruce and Scotch pine in Norway, the proper age is between seventy and one hundred years. The ash, larch, and elm, may be cut when the trees are between fifty and ninety years old; and between thirty and fifty years is a proper age for poplars.
The felling of timber was looked upon by ancient architects as a matter of much moment. According to Vitruvius, the proper time for felling is between October and February, and he directs that the trees should be cut to the pith, and then suffered to remain till the sap be drained out. The effusion of the sap prevents the decay of the timber, and when it is all drained out, and the wood becomes dry, the trees are to be cut down, when the wood will be excellent for use. A similar effect might be produced by placing the timber on its end as soon as it is felled, and it would, no doubt, compensate for the extra expense by its durability in use. In France, so long ago as 1669, a royal order limited the felling of naval timber from the 1st October to 15th April, when the “wind was at north,” and “in the wane of the moon.” Buonaparte directed that the time for felling naval timber should be “in the decrease of the moon, from 1st November to 15th March,” in order to render it more durable. In England, in the first year of James I., there was an Act of Parliament prohibiting every one from cutting oak timber, except in the barking season, under a severe penalty.
James I. was not the only English sovereign who has been concerned with timber trees; for King John was obliged to cancel at Runnemede the cruel forest laws enacted by his father, William the Conqueror, especially those restricting the people from fattening their hogs.
Up to a recent period large droves of hogs were fattened upon the acorns of the New Forest in Hampshire. At the present time the hogs of Estremadura are principally fed upon the acorns of the Ballota oak; and to this cause is assigned the great delicacy of their flesh.
A Berkshire labourer, living near Windsor Forest, thus speaks of the delicacy of acorn-fed pork: “Well, that be pretty like the thing. I hadn’t tasted the like o’ that this many a day. It is so meller—when you gets your teeth on it, you thinks you has it; but afore you knows where you is, ain’t it wanished!”
There is another point in connection with the time of felling timber, which ought to be noticed. It is a widespread opinion that trees should be felled during the wane of the moon. This planetary influence is open to doubt, but the opinion prevails wherever there are large forests. Columella, Cato, Vitruvius, and Pliny, all had their notions of cutting timber at certain ages of the moon. The wood-cutters of South America act upon it, so do their brethren in the German forests, in Brazil, and in Yucatan. It was formerly interwoven in the Forest Code of France, and, we believe, is so still. Vitruvius recommends this custom, and we find Isaac Ware writing of the suggestion: “This has been laughed at, and supposed to be an imaginary advantage. There may be good in following the practice; there can be no harm: and therefore, when I am to depend upon my timber, I will observe it.” The Indian wood-cutters believe that timber is much more liable to decay, if cut when the moon is in crescent.
An American writer, in 1863, thus writes of his experience in the matter: “Tradition says that the ‘old’ of the moon, in February, is the best time to cut timber; but from more than twenty years of observation and actual experience, I am fully convinced it is about the worst time to cut most, if not all kinds of hard-wood timber. Birch, ash, and most or all kinds of hard wood will invariably powder-post if cut any time in the fall after the tree is frozen, or before it is thoroughly leaved out in the spring of the year. But if cut after the sap in the tree is used up in the growth of the tree, until freezing weather again comes, it will in no instance produce the powder-post worm. When the tree is frozen, and cut in this condition, the worm first commences its ravages on the inside film of the bark, and then penetrates the wood until it destroys the sap part thereof. I have found the months of August, September, and October, to be the three best in the year to cut hard-wood timber. If cut in these months, the timber is harder, more elastic, and durable than if cut in winter months. I have, by weighing timber, found that of equal quality got out for joiners’ tools is much heavier when cut and got out in the above-named months than in the winter and spring months, and it is not so liable to crack. You may cut a tree in September, and another in the ‘old’ of the moon in February following, and let them remain, and in one year from the cutting of the first tree, you will find it sound and unhurt, while the one last cut is scarcely fit for firewood, from decay. Chestnut timber for building will last longest, provided the bark be taken off. Hemlock and pine ought to be cut before being hard frozen, although they do not powder-post; yet if they are cut in the middle of winter, or in the spring of the year, and the bark is not taken off, the grub will immediately commence its ravages between the bark and the wood. I have walnut timber on hand which has been cut from one to ten years, with the bark on, which was designed for ox-helves and ox-bows, and not a worm is to be found therein; it was cut between 1st August and 1st November. I have other pieces of similar timber cut in the winter months, not two year’s old, and they are entirely destroyed, being full of powder-post and grub-worms.”
What shall we say when doctors disagree? The theory given to account for what is assumed to be a fact, is, that as the moon grows the sap rises, and the wood, therefore is less dense than when the moon is waning, because at that time the sap in the tree diminishes. No evidence whatever can be offered in support of the theory, and one would certainly imagine that the rise or fall of the sap would depend on the quantity of heat which reaches the foot of the tree, and not at all on attraction.
All investigations tend to prove that the only proper time for felling timber is that at which the tree contains the least sap. There are two seasons in each year when the vessels are filled. One is in spring, when the fluid is in motion to supply nutriment to the leaves, and deposit material for new wood; the other is in the early part of autumn, when, after the stagnation which gives the new wood time to dry and harden, it again flows to make the vegetable deposits in the vessels of the wood. At neither of these times should trees be felled; for, if the pores be full of vegetable juices, which being acted upon by heat and moisture may ferment, the wood will decay. Of the two periods, the spring must be the worst, because the wood then contains the greatest quantity of matter in a state fit for germination.
The results of a series of experiments made in Germany show that December-cut wood allows no water to pass through it longitudinally; January-cut wood passed in forty-eight hours a few drops; February-cut wood let two quarts of water through its interstitial spaces in forty-eight hours; March-cut wood permitted the same to filter through in two and a half hours. Hence the reasons why barrels made from wood cut in March or April are so leaky, as the sap is then rising, and the trees are preparing to put forth their leaves.
It thus happens that the time for felling is midsummer or midwinter. The best time for felling, according to some, is midsummer, when the leaves are fully expanded, and the sap has ceased to flow, and the extraneous vegetable matter intended for the leaves has been dislodged from the trunk of the tree by the common sap, leaving it in a quiescent state, and free from that germinative principle which is readily excited by heat and moisture, and if the timber were cut while it remained, would subject it to rapid decay and to operations of worms. Midwinter, amongst some, is chosen as a time for felling, as it is stated that winter-felled heart-wood is less affected by moisture, and likely to be the best and most durable; but as the only peculiar recommendation which that time possesses is the facility which it affords for gradual seasoning, by which timber is rendered less liable to split and get distorted, and slow drying being generally available at any season under shade and shelter, midsummer appears for many obvious reasons the most expedient. In general, all the soft woods, such as elm, lime, poplar, willow, should be felled during winter. In some kinds of trees a little after midsummer appears to be decidedly the best time for felling. Alder felled at that time is found to be much more durable; and Ellis observes, that beech when cut in the middle of summer is bitter, and less liable to be worm-eaten, particularly if a gash be cut to let out the sap some time before felling. Mr. Knowles states that, “About Naples, and in other parts of Italy, oaks have been felled in summer, and are said to have been very durable.” Most of the trees in southern Italy are felled in July and August, and the pines in the German forests are cut down mostly in summer time, and it is stated that their wood is sound.
The following are advocates for winter felling, viz. Cato, Pliny, Vitruvius, Alberti, Hesiod, De Saussure, Evelyn, Darwin, and Buonaparte. Some of them consider that winter-felled timber, which has been barked and notched in the previous spring, loses much of that half-prepared woody matter, containing seeds of fungi, &c., that there is no doubt of its superiority to summer-felled timber.
The age at which trees should be felled, and the most suitable time for the work having been determined, there are two other things which claim attention.
The first of these is the removal of the bark from the trunk and principal branches of the tree. For, in oak trees, the bark is too valuable to be lost; and as the best period for the timber is the worst for the bark, an ingenious method has been long partially practised, which not only secures the bark at the best season, but also materially improves the timber. This method consists in taking the bark off the standing tree early in the spring, and not felling it till after the new foliage has put forth and died. This practice has been considered of inestimable value; for by it the sap-wood is rendered as strong and durable as the heart-wood; and in some particular instances experiments have shown it to be four times as strong as other wood in all respects similar, and grown on the same soil, but felled with the bark on and dried in sheds. Buffon, Du Hamel, and, in fact, most naturalists, have earnestly recommended the practice. Evelyn states, “To make excellent boards, bark your trees in a fit season, and let them stand naked a full year before felling.”
In regard to the time that should elapse between the removal of the bark and the felling of a tree, a variety of opinions exist. It was the usual custom of early architects to remove the bark in the spring, and fell the trees during the succeeding winter. Later investigations seemed to have proved that it is better to perform the work three or even four years in advance, instead of one, although Tredgold appears to think one year too long. Trees will, in most situations, continue to expand and leaf out for several seasons after the bark has been removed. The sap remaining in the wood gradually becomes hardened into woody substance, thereby closing the sap vessels and making it more solid. As bark separates freely from the wood in spring, while the sap is in motion, it should be taken off at that period. When the above method is not adopted, it is well either to pierce the trunk some time before felling to drain out the sap, or immediately on its being felled to set it on end.
The second suggestion is, to cut into and around the entire trunk of the tree, near the roots, so that the sap may be discharged; for in this manner it will be done more easily than it can be by evaporation after the tree is felled. In addition to this, if it be permitted to run out at the incision, a large portion of the new and fermentable matter will pass out with it, which would remain in the wood if only such material is removed as would pass off by evaporation. This cutting should be made in the winter previous to the August in which the tree is to be felled; and the incision should be made as deep into the heart-wood as possible without inducing a premature fall of the tree.
The custom of ringing or girdling the tree before felling has been advocated, on the ground that the seasoning is thereby expedited, and also more thoroughly effected. This is doubtful, at least, in oil-containing trees (as teak, &c.), but the practice appears to be contra-indicated for other reasons: when a tree has been ringed, many wood-cutters object to cut it down on account of its increased hardness. This objection might be waived, were it not for another and more serious one which has been adduced. It is believed to be a fact by some that trees felled after girdling have the heart shake increased. It is difficult to explain this, if it be actually the case.
Many suggestions might be made as regards the mechanical operation of felling trees, with which ancient nations were not unfamiliar:
… “for thou knowest that there is not among us any that can skill to hew timber like unto the Sidonians.”—1 Kings v. 6.
But as these operations are familiar to all intelligent workmen, it is only necessary to mention one, viz. the value of removing from the side of the tree such branches as will strike the ground when it falls, and, by wrenching, cleave the grain of the wood, and thereby injure the timber. Such defects, which are often found after the timber has been seasoned, could not be discovered when it left the mill.
In conclusion, we can truly state that the most extensive felling of trees for one building only which we have ever heard or read of is the following:
“And Solomon had threescore and ten thousand that bare burdens, and fourscore thousand hewers in the mountains.”—1 Kings v. 15.
CHAPTER IV.
ON SEASONING TIMBER BY NATURAL METHODS, VIZ. HOT AND COLD AIR; FRESH AND SALT WATER; VAPOUR; SMOKE; STEAM; BOILING; CHARRING AND SCORCHING, ETC.
All timber must, whether it be sap-wood or heart-wood, be placed in situations which will allow the sap to exude or evaporate, and this process is the one technically known by the term “seasoning.” There are natural and artificial modes of seasoning, both of which have their recommendations; but the former has certainly the right of preference, as it gives greater toughness, elasticity, and durability, and therefore should always be employed in preparing timber for carpentry. As the word “timber” has been frequently used, it may be as well to state that it is derived, according to Dr. Johnson, from the Saxon, timbrian, to build: hence the above definition. The legal definition of timber is restricted to particular species of wood, and custom varies in different countries as to the species ranked among the timber trees.
When a tree is felled, it encloses in its fibres as well as in capillary channels a considerable quantity of sap, which is nothing else but water charged with gummy, saccharine, saline, mucilaginous, and albuminous matters. In this state, the latter are very liable to ferment, but they lose their liability when, by the evaporation of the sap, they pass to a dry and solid state; so that the first suggestion which naturally presents itself to the mind, is to subject the timber to a lengthened seasoning.
But the present demands for time will not admit of this, and therefore it is imperative to resort to artificial and speedy methods.
With respect to the value of timber in the log, owing to its becoming rent by the weather, it sells for 15 per cent. less the second year than the first, and so on for less and less the longer you keep it.
A natural seasoning may be adopted for specimens of moderate thickness, such as deals, planks, &c. At the end of eighteen months from the time of importation they are scarcely dry enough for the consumer’s use.
When there is time for drying it gradually, all that is necessary to be done on removing it from the damp ground of the forest, is to place it in a dry yard, sheltered from the sun and wind, and where there is no vegetation; and set it on bearers of iron or brick in such a manner as to admit of a ventilation all round and under it. In this manner it should continue two years, if intended for carpentry; and double that time, if intended for joinery; the loss of weight which should take place to render it fit for the purposes of the former being about one-fifth; and for the latter about one-third. In piling it, the sleepers on which the first pieces are laid should be perfectly level, and “out of the wind,” and so firm and solid throughout that they will remain in their original position; for timber, if bent or made to wind before it is seasoned, will generally retain the same form when dried. Blocks of wood should be put between the “sticks” of timber, and each piece directly over the other, so that air may freely pass through the whole pile; for while it is necessary to shield timber from strong draughts of wind and the direct action of the hot sun, a free circulation of air and moderate warmth are equally essential.
PLANS of different BALTIC MODES of CUTTING DEALS for the ENGLISH and FRENCH MARKETS.
THE SMALLEST TREES ARE CUT FOR DEALS; THE LARGEST FOR LOGS.
OLD MODE OF CUTTING.
- ENGLISH BATTEN. 7IN × 2½IN
- ENGLISH DEAL. 9IN × 2½IN
- ENGLISH DEAL. 9IN × 2½IN
- ENGLISH BATTEN 7IN × 2½IN
- 9 × 2½ = 22½ × 2 = 45in
- 7 × 2½ = 17½ × 2 = 35/80
MODE PRACTISED UNTIL THE FRENCH MARKET IMPROVED.
- ENGLISH BATTEN. 7IN × 2½IN
- ENGLISH DEAL. 9IN × 3IN
- ENGLISH BATTEN. 7IN × 2½IN
- 9 × 3 = 27 = 27in
- 7 × 2½ = 17½ × 2 = 35/62
MODE GENERALLY ADOPTED AT THE PRESENT TIME.
- FRENCH DEAL. 9IN × 1¼IN
- ENGLISH DEAL. 9IN × 3IN
- ENGLISH DEAL. 9IN × 3IN
- FRENCH DEAL. 9IN × 1¼IN
- 9 × 3 = 27 × 2 = 54in
- 9 × 1¼ = 11¼ × 2 = 22½/76½
Notes on Deals.
All deals are liable to dry rot, if placed in contact with damp brickwork.
If the pith of a tree be left in the centre of a deal, dry rot attacks it.
Dry rot first attacks the sapwood of a deal; and next, the pith.
Stockholm, or Gefle deals are not liable to be affected with dry rot.
“STRONG” DEALS rend. When sawn, they do not give saw dust, but the fibres tear.
BEST DEALS are light, mellow, and exhibit a silky texture when planed.
“BESTS”. Wholly free from knots, shakes, sapwood, or cross grain, and well seasoned.
“SECONDS”. Free from shakes, and sapwood: small knots allowed.
“THIRDS”. All that remains after “bests” and “seconds” have been picked out.
If timber is not used round, it is good to bore out the core; as, by so doing, the drying is advanced, and splitting prevented, with almost no sacrifice of strength. If it is to be squared into logs, it should be done soon after some slow drying, and whole squared, if large enough, as that removes much of the sap-wood, facilitates the drying, and prevents splitting, which is apt to take place when it is in the round form, in consequence of the sap-wood drying before the heart, from being less dense. If it may be quartered, it is well to treat it so after some time, as the seasoning is by that means rendered more equal. It is well also to turn it now and then, as the evaporation is greatest from the upper side. In France, the term “bois du brin,” means timber the whole size of the tree, excepting that which is taken off to render it square.
To prevent timber warping to any serious extent, it should be well seasoned before it is cut into scantlings; and the scantlings should be cut some time before they are to be used, in order that the seasoning may be as perfect as possible; and if they can be set upright, so much the better, as then they will dry more rapidly. The white lowland deals of Norway and the white spruce deals of Canada have the same disposition to warp and split on drying. Du Hamel has shown that it is a great advantage to set the timber upright, with the lower end raised a little from the ground; but as this cannot always be done, the timber-yards should be well drained and kept as dry as possible. “Ancient architects,” observes Alberti, “not only prevented the access of the scorching rays of the sun and the rude blasts of wind, but also covered the surface with cow-dung, to prevent the too sudden evaporation from the surface.” The warping of timber is attributable by some to the manner of its growth. Boards cut out of a tree that is twisted in its growth will not keep from warping; boards cut from trees that are grown in open situations have another fault, in the heart of the tree not running straight like forest-grown wood. In a plank cut from a tree of this kind in a straight line, the heart will traverse it from one end to another. No treatment will prevent it from warping or drying hollow on the side farthest from the heart. Where the heart is in the centre of a plank, and each side has an equal chance of drying, it will not warp; but there will be a shake or crack upon each side, denoting the position of the heart.
Some deals, and particularly the stringy deals, are very hygrometric, and never lose the property, however long they have been seasoned, of expanding and contracting with change of weather. White Petersburgh deals are said to have that property, however long they may have been kept, so that if used in the panel of a door, the wood alternately enters and recedes from the groove into which it fits, as the paint will show when that kind of deal has been used for a panel.
The wood of the north side will not warp so much as the wood from the south side. The face of the planks should be cut in the direction which lay from east to west as the tree stood. If this be done, the planks will warp much less than if cut in the opposite direction. The nature of the tree, the soil upon which it is grown, the position of its growth, the period of the year in which it is felled, and the length of time between its felling and converting, are the principal points to be considered; a thorough knowledge and study of which is the only true principle on which we can hope to deal with the warping and converting of timber.
Wood, when it is cut into small pieces, very soon acquires its utmost degree of dryness. Dr. Watson, Bishop of Llandaff, in the month of March, cut a piece from the middle of a large ash tree that had been felled about six weeks, and weighed it; its weight was 317 grains. In seven days it lost 62 grains, or nearly one-fifth of its weight. It was weighed again in August of the same year, but had not lost any more of its weight; hence it had become perfectly dry in the short space of seven days. He also found that the sap-wood of oak lost more weight in drying than the heart-wood, in the proportion of 10 to 7.
The time that is required to season or dry a piece of timber obviously depends upon its magnitude; as a general rule, large timbers will not continue good so long as small ones, as sufficient time is rarely given for a thorough seasoning. The time required to dry a piece of timber, all other things being alike, will depend on the quantity of surface exposed to the action of the air; therefore, while the quantity of timber remains the same, the larger the surface, the sooner it will dry. Also, if the quantity of surface remains the same, the time of drying will be proportioned to the quantity of matter; as the greater the quantity of matter under the same surface, the longer it will be in drying.
As drying proceeds most rapidly in small pieces, it is therefore important to reduce the timber to its proper scantlings or size for use; for however dry a piece of timber may be, when it is cut to a smaller scantling it will shrink and lose weight, being always less dry in the centre than at the surface; and the more rapidly the drying has been carried on, the greater will be the difference. Nevertheless, in the first stage of seasoning it is best that it should proceed slowly; otherwise, the external pores shrink so close as not to permit the full evaporation of the internal moisture, and the piece would split from unequal shrinking; and lastly, it should be reduced to the proper scantling, as already observed, some time before it is to be framed. Various tables have been given by writers on timber, the result of algebraical calculations, of the times of seasoning and drying for different woods of different lengths, breadths, and thicknesses, in the open air; but as wood even of the same description and quality varies so much, this matter is best left to those who are well acquainted with timber. It may, however, be stated that the time required for drying under cover is shorter than in the open air, in the proportion of 5 to 7.
The English shipwright considers that three years are required to thoroughly season timber. The timbers for ships are usually cut out to their shape and dimensions for about a year before they are framed together, and they are commonly left a year longer in the skeleton shape to complete the seasoning, as in that condition they are more favourably situate as regards exposure to the air than when they are closely covered in with planking.
It is worthy of mention that all the harder woods require increased care in the seasoning, which is often badly begun by exposure to the sun or hot winds in their native climates: their greater impenetrability to the air the more disposes them to crack, and their comparative scarcity and expense are also powerful arguments on the score of precaution. Oak timber requires to be very carefully seasoned, as it is generally used in buildings for the best description of work, and should unseasoned oak be used for “panelling,” any shrinkage will be fatal to the work. Mr. George Marshall, timber merchant (see the Builder, January 20, 1872), with respect to seasoning oak timber, observes: “I should select oak trees known to be old and hearty, with clean, straight butts, from 15 inches to 20 inches in diameter. I should then have the bark taken off as they stand, and leave them thus till the winter; the sap will then partially dry out, and make the wood a rich brown colour. As soon as they are cut down, have them sawn up at once into the lengths you require the panelling, 6 inches or 8 inches wide and 1 inch to 1½ inch thick. Be careful to cut all the heart shakes, by having one cut through the centre of the log before edging the boards to the required width. With regard to the drying process, stack the boards in a shed with a good draught through it, and load them down, with slips between each board, to prevent warping. If this be done they will be found to dry well and speedily, and they will not require to be exposed to the weather.”
Sir. Robert Phillips, on seasoning oak for panelling, states: “If the tree is large enough for the purpose, cut it into four, in sections, by drawing a vertical and horizontal line across the end, meeting in the centre. If too small for this, cut it into 4½ inch or 6-inch plank, as soon as possible after felling, and then stack on end out in the open: do not lay on the ground, but stand it as nearly vertical on its end as possible, and keep it wet during the first three months. If the weather is dry, well wet it with water poured on the top, and allowed to run down. Let the ends stand on a piece of quartering, to keep it out of the dirt, or it will be stained some distance up. After standing thus for some six months, after putting it in a dry place for some time, cut it into the scantlings you require, always bearing in mind that oak will, after this seasoning, shrink at least half an inch to a foot, in width and thickness. They should then be stacked and stripped, and covered with spare boards, and weighted on the top, for at least six months—as much more as possible—in a covered shed, with plenty of air, occasionally turned over and shifted, till they are dry enough to make dust when planed, and not turn the shaving black. They will then be fit for use.
“I should advise for the panels to be cut feather-edged boards, in radial lines from the centre of the tree: it will be a waste of material, but will repay in the beauty of the wood, and the way it will stand without warping. Most of the panels of our old cathedrals were rent (not sawn) in this way, and stand admirably. The butt of the tree should be taken, the top being used for a rougher purpose.”
Mr. George Marshall and Mr. Robert Phillips might have mentioned that the oak trees should be of the Quercus Robur species, and not the Quercus Sessiliflora. They are easily distinguished when growing by the following peculiarities: The acorn-stalks of the Robur are long; the acorns grow singly, or seldom two on the same footstalk; the leaves are short. The acorn-stalks of the Sessiliflora are short; the acorns grow in clusters of two or three, close to the stem of the branch; the leaves are long.