Lesson the Second.
Paul was greatly pleased with the method adopted by his cousin for giving him the first notions of building. In the evening he presented as his day’s work a fair transcription of all that his teacher had explained to him on the ground. He even illustrated his text by some pretty good diagrams. The corrections were quickly made after dinner. But next day the incessant rain prevented them from going out, and Eugène decided that the second lecture should be given in the house. “We shall have illustrations enough before us; the château itself will supply them. We will go through it from cellar to attic, and study its materials and methods of construction—to criticize them if they are bad, or to take note of them if they are good.” When teacher and pupil had gone down into the cellars, Eugène began by saying, “Look how damp this cellar wall on the side of the courtyard is; and see how the mortar in the joints of the stones has fallen, owing to two causes:—first, in building these walls, the precaution was not taken of cementing them on the outside, so as to make the water in the ground run down to the bottom; second, the mortar employed in the building was not made with hydraulic lime. There are two principal kinds of lime: fat or rich lime and hydraulic lime. The first is obtained by burning the compact limestones usually found at the top of the beds; it is called fat because when slaked it is glutinous and sticks to the tool with which it is mixed; this lime, on being immersed in water, swells and sends forth a dense vapour, as you may have observed, and mixed with sand is slow in setting. Employed above ground, mortars made with this lime become at length very hard, but retain more or less for a time a certain plasticity. These mortars, however, as they are slow in setting, are readily softened by water, and cannot then ever harden. Hydraulic limes, on the other hand (obtained by burning the lias limestones), when mixed with sand, soon become very hard, and set all the better for being in a damp place. Hence this lime is called hydraulic, because it is employed for all masonry-work under water. In default of lias limestones, artificial hydraulic limes are made, by grinding a certain proportion of clay with a limestone suitable for making ordinary lime. Hydraulic lime is tested by slacking—that is to say, mixing it with water; when it slakes with the production of very little vapour.
“It is with hydraulic lime that concretes, of which I spoke to you yesterday, are made. The mortar being prepared, a certain proportion of hard gravel, about the size of eggs, is mingled with it; the whole is well mixed and thrown into the excavations, where it is rammed with wooden rammers. If the lime is good and the concrete well made, it forms a veritable rock, similar to the conglomerates or pudding-stone of natural formation. As, when set, water penetrates with difficulty through these concretes, they prevent that percolation of subjacent water to which cellars made in wet grounds are liable.
“If the wall you see there had been built with mortar made with hydraulic lime, it would have been sound, and the mortar joints would have been as hard as the stone itself. You will easily understand that when the water has gradually softened and liquefied the mortar in the beds and joints at the base of a wall, the stones which compose it settle, and all the rest of the building suffers. That is why the front of the house, towards the court, presents a considerable number of cracks, that are filled in from time to time, but of course with no result in doing away with the cause of the mischief.
Fig. 9
Fig. 10.
“You observe that the cellar wall which receives the arch of the vault is very thick, much thicker than is the wall of the ground floor. The latter is scarcely 2 feet thick, whereas this is full 3 feet. This additional thickness is given to the inside principally to receive the springing of the vault. A sketch will enable you to understand the reason of this arrangement. Let A (Fig. [9]) be the thickness of the wall of a house on the ground floor—a thickness of 1 foot 8 inches if cellars are wanted beneath the ground floor; the floor line being at B and the outside ground line at C, it will be well first to indicate the floor line by a projection,—a greater thickness given to this wall on the outside, say of 2 inches. At A, then, the wall will have a thickness of 1 foot 10 inches. Your cellar arch being drawn at D, we must reserve a resting-place of at least 8 inches, to receive the first arch-stones of the spring of the vault; then it is well to give on the side next the ground a greater projection, to make a good footing for the plinth; this projection being 2 inches, we shall have at F a thickness of 2 feet and at G 2 feet 8 inches at least, as it will not do for the wall which rises to bear on the oblique beds of the vault, otherwise it would not have a solid footing, and would be weakened or reduced in thickness by this arch, which would penetrate it, as we see in the drawing I. But come here into this other cellar, which belongs to the oldest part of the château, and is built with good stones. The builder did not wish to lose space within, and as he built with worked stone he sought to economise material. What, then, did he do? (Fig. [10.]) He gave his cellar wall only the thickness of that of the ground floor; at regular distances he put massive corbels 2 feet above the floor; upon these corbels he carried arches projecting 10 inches, and on these arches, which replace the extra thickness or counter-wall of which I spoke to you just now, he carried his vaulting arch. This perspective sketch will enable us readily to understand this method of construction. The upper wall thus leaves the vault perfectly free and rises plumb over its lower face.
“Is it all clear to you? Well, let us go and look at that little flight of steps which perhaps you have never attentively examined. It is 4 feet 3 inches wide, which was large enough to afford a passage to the queues of wine. Observe (Fig. [11]): the ramping vault is composed of as many arches, one above another, as there are steps; that is extremely well managed, solid and easily built. In fact, when the stone steps are laid, over above them is successively fixed the same wood centre which, of course, is raised at each step; and upon this centre an arch is built, which is quickly done, as the stones are worked ready. In this way the arches follow the section of the steps, and the centre being shifted—after each arch is keyed—to the next step commencing from the bottom, two men can turn five or six of these arches in one day, so that if there are twelve steps, this ramping vault may be built in two days. Look, I will show you how this construction should be denoted in perspective and geometrical section in your résumé to-day—A and B.
Fig. 11.
“Let us go up to the ground floor. Look at the efflorescence resembling cotton wool on the interior of the walls: it is the saltpetre which forms inside the stone, and, through the humidity of the ground, crystallizes on the surface. This saltpetre affects the stone injuriously, ultimately eats it away, and throws off any painting that we might endeavour to use as a counteractive on the interior surface. Mastic cements are made to stop the effects of the saltpetre, but these means only delay its appearance for a short time without curing the evil, and this cement soon falls off in a crust. It is therefore necessary in building, especially in the country, to prevent the damp of the ground from rising up in the walls, and to stop it at the ground level. The interposition of a layer of pitch beneath the plinth has sometimes been tried, in order to prevent the absorption of damp by the stones—or what is called capillary attraction—but this method is very inefficient. The pitch oozes out under the pressure, as it does not harden sufficiently to bear that pressure, or it decomposes and combines with the lime. The best plan is to lay a course of slates in the mortar-bed between the first lower courses of the plinth. The slate effectually hinders that effect of capillary attraction, and the damp is unable to rise in the walls.
Fig. 12.
“Now observe this front wall in the court: it forms a protuberance at the floor level of the first story. We call that a bulging of the wall. Instead of preserving its vertical plane, as it should have done, it has bulged out; and why? Because it has been thrust out by a force acting from within outwards. What is that force? It might be an arch; but there is no arching on the ground floor. It can therefore be only the floor. It is not clear at first sight how a floor, which is a horizontal plane, can thrust; for to thrust, we must suppose the floor to expand in one direction, which cannot be. But see what happens. Give me your best attention.... Formerly, to compose a floor, large beams were laid from wall to wall, and upon these beams lighter pieces of timber, called joists; then on these was laid a bed of earth, gravel, or sand, and upon that a surface of mortar to receive the tiling. This made a very heavy mass. Now, as a piece of timber, even of considerable section, bends in time under its own weight—that is to say, from being straight becomes curved—its tendency to bend will be proportionally greater when it is weighted. The more it bends, the more powerful its thrust upon the inner surface of the walls in which it has its bearing. It is this pressure upon the interior surface that tends to thrust the wall outwards. But if, as in this case, in order to relieve the bearing of the beams, struts of wood have been put underneath (Fig. [12]), this effect of thrust is all the more sensible because the arm of the lever is longer. You do not quite understand, I see. A sketch will make it clear to you. Let A be the section of the wall, or, if you will, its thickness. If the beam bends according to the line C D, there occurs a pressure at D, which produces a thrust at F and the rounding of the wall, as indicated by the dotted curves. Supposing even that in lieu of the strut E we have a stone corbel, the effect produced will be the same, though less forcible, unless the tail of the corbel reaches through the wall, as you see marked at I, and this tail K is weighted in such a manner that the weight neutralizes the pressure which the beam exerts at the end L. This has not been done here, where instead of the wood strut, a corbel was put. This corbel has but a middling hold in the wall, and the latter, formed of small stones not very well built, has not sufficient cohesion to resist the thrust exerted by the deflection of the beams. But why, you will ask me, has this effect been produced at the floor level of the first story and not above? Because, by the effect of the bulging we find here, the wall has inclined above towards the inside, and has thereby squeezed the second floor—its surfaces being placed, by their very inclination, perpendicularly to the curve line of the upper beams, as I indicate to you at M, exaggerating the effect for the purpose of making it clearer.
“You see that each detail merits attention, and that the builder ought to have a good reason for everything he does.
“In work of every kind we learn to avoid faults only by analysing and searching into their causes and ascertaining their effects. To become a good builder, therefore, it is not enough to familiarize one’s self with rules of construction, which cannot provide for all contingencies; we must see and observe much, and ascertain defective points in buildings that have been tested by time; just as physicians become able to determine what a good constitution is only by studying diseases and their causes. For the most part we appreciate what is good only through observing what is bad; if, in the absence of the bad, we are able to admit that there is such a thing as the good. An old proficient in architecture, who, when I was about your age, was so kind as to aid me with his advice, used often to say to me: ‘I can tell you, my dear fellow, what you must avoid in the art of building;—as to explaining to you in what the good and the beautiful consist, you must find out that yourself. If you are a born architect, you will know well enough how to discover it; if not, all that I could show you, all the examples I could place before you, would not give you talent.’ And he was right. The sight of the finest works in architecture may pervert the minds of students, if it’s not been explained to them how the authors of these works succeeded in making them beautiful by having avoided such or such faults.
“But you have enough to write out for to-day. Make a fair copy of these sketches opposite your text, and we will examine it this evening.”
CHAPTER VI.
HOW PAUL IS LED TO RECOGNIZE CERTAIN DISTINCTIONS BETWEEN ETHICS AND ARCHITECTURE.
When, in the evening, Paul’s report of the lesson was read in the family circle, M. de Gandelau interrupted the reading at this phrase incorrectly given, “Good is only the absence of evil.”
“Oh, oh!” said his father; “Charity is something more than the absence of evil. If you give nothing to the poor man who asks bread of you; if, being able to swim, you do not try to save a drowning man, you do not do evil, but certainly you do not do good.”
“That is not exactly what I said to Paul,” replied Eugène, smiling. “Respecting defects discovered in building, I said, ‘I believe that the good is the absence of the bad;’ that is to say, in building operations, and perhaps in many other matters belonging to the purely material order of things, to avoid what is bad is to do well, but not to do good. I must, however, admit that I did not sufficiently develop my thought.
“Two things are needed to make a good builder: clear-sighted intelligence—which depends on our individual psychical nature—and the experience we acquire.
“Observation and experience thence resulting enable us to recognize what is defective and to avoid it; but if, notwithstanding the advantage thence derived, we are not endowed by nature with clear-sighted intelligence, experience, though enabling us to avoid the bad, does not of itself suffice for the discovery of the good.
“Moreover, though in morals the good is absolute and independent of circumstances, it is not the same with building. What is good here is bad elsewhere, on account of climate, habits, nature of materials, and the way in which they are affected by local circumstances. While, for instance, it is desirable to cover a roof with slates in a temperate and humid climate, this kind of roofing is objectionable in a warm, dry, and windy climate. Wooden buildings will be excellent in one situation and unsuitable in others. While it is desirable to admit the light by wide openings and to glaze large surfaces in northern climates, because the sun’s glare is subdued, this would be objectionable in southern countries, where the light is intense, and where it is necessary to procure shelter from the heat. A code of morals is possible, but we cannot establish absolute rules in building; experience, reasoning, and reflection must therefore always be summoned to our aid when we attempt to build. Very often young architects have asked me what treatise on building I should recommend as the best. There is none, I tell them; because a treatise cannot anticipate all contingencies,—all the special circumstances that present themselves in the experience of an architect. A treatise lays down rules; but ninety-nine times out of a hundred you have to encounter the exception and cannot rely upon the rule. A treatise on building is useful in habituating the mind to devise plans and have them put into execution according to certain methods; it gives you the means of solving the problems proposed; but it does not actually solve them, or at least only solves one in a thousand. It is then for intelligence to supply in the thousand cases presented what the rule cannot provide for.”