Within the present century, the annual use of bricks in Great Britain has more than doubled, owing to the increase of manufactories, and to the construction of railroads and other public works.
Making Bricks by Machinery.
Within the last few years the making of bricks and tiles by machinery has occupied much attention. A large number of patents has been taken out for contrivances having this object in view. In some cases the patentee has directed his attention chiefly to the preparation of bricks for houses; while in others the making of tiles for draining has been the chief object. A description of one or two of these contrivances will give an idea of the general character of the whole.
The Marquis of Tweeddale, having his attention drawn to the importance of employing draining tiles in agriculture, directed his talents to the invention of a machine which should make them so quickly as to enable them to be sold at a low price. After many attempts, he perfected a machine which worked out this object, and at the same time possessed all the facilities for making common bricks. The machine is not constructed on the principle of imitating the manual operation, by forming the bricks in moulds; but it arrives at the same end in a different and remarkable manner. The principle adopted is, to form and protrude, by mechanical means, a continuous fillet of clay, of the proper width and thickness for a brick, and to stop this act of protrusion for a moment, whilst a length of the fillet equal to that of a brick is cut off. This is effected by the following mechanical arrangements:—Two vertical roller-wheels, one of them being placed over the other, and having an interval between them equal to the thickness of the intended bricks or tiles, are made to revolve in contrary directions; consequently they draw between them the clay with which they are fed on the one side (either by hand or by any mechanical contrivance), and deliver it on the other in a highly compressed state, and in the form of a straight, smooth, and even fillet of the width of the rollers. To provide for the squareness and smoothness of the sides of the fillet, the sides of the aperture through which the clay passes are made square and neat, so as to prevent the clay from spreading out laterally. The clay is supported in a horizontal position whilst delivered to and received from the rollers, upon a short endless band on each side revolving on rollers rather close together; and in order to facilitate this object the rollers themselves have bands, which are prolonged in the direction of the endless bands in such a manner as to meet them, and form one horizontal line of support. These bands are made of fustian, the nap of which prevents the adhesion of the clay. The rollers are so acted on by the working power that they protrude a length of clay equal to the required length of the brick or tile, and then stopping, they allow time for a straight stretched wire to descend and cut off the brick or tile, after which the motion between the rollers is resumed, until another length is protruded, and so on continuously. The fillet of clay is double the width for a brick, and a wire is kept constantly stretched in the middle of its path, dividing it into two fillets, so that two bricks are cut off at once. Two boys are sufficient to remove the bricks as fast as they are produced, which is at the rate of from fifteen to eighteen hundred in an hour. The consistence of the clay is so much stiffer than that used for hand-made bricks, that only half the time is required in the drying. From there being so little water in the clay, and from its undergoing so much compression, the bricks produced are remarkably dense and strong, weighing half as much again as the ordinary brick, and absorbing only one-seventh as much water.
Many machines have been contrived, having for their object the formation of bricks on a principle somewhat analogous. Another class of machines have effected the desired end in a different way,—viz., by forming each brick separately in a mould. A slight description of one machine of this kind will illustrate all the others. The main part of the machine is a horizontal wheel of large diameter. Round the periphery of this wheel is a series of moulds, the exact size and shape for bricks, placed nearly close together. Each mould has a loose bottom, incapable of falling below the mould, but capable of rising to its upper edge. The clay for the bricks, being properly prepared in vessels at one side of the wheel, is made to fall into one of the moulds, and the superfluous quantity is scraped off by a flat edge which passes over the mould. The wheel rotates, and in its movement it passes over a circular inclined plane, so constructed as to lift the bottom of the mould up, so as to protrude the newly-made brick above the mould, where it can be conveniently taken off by the hand. All the different moulds, perhaps thirty or forty in number, are at any given instant in different conditions as to their quota of clay; one is receiving the clay, another is having the superfluous clay scraped off, another has travelled so far round as to have the brick lifted halfway out of it, another presents the brick wholly out of the mould, ready to be taken off, while the others are travelling on empty to receive a new supply of clay, all the moveable bottoms gradually sinking to their proper position as the wheel proceeds, so that one rotation of the wheel carries each mould through all its different stages of position.
The Processes of Bricklaying.
When we consider that a wall forty or fifty feet high, and not more than two feet thick at the bottom, and fourteen or fifteen inches thick at the top, is constructed of such small bodies as bricks, we may well suppose that considerable nicety in workmanship must be requisite to give stability to such a structure. The uniformity in size in the bricks themselves, arising from their being copies of one mould, is obviously the first condition that tends to the object; the next is, that they should be put together in such a way as to cause them mutually to adhere, independently of the tenacity of the mortar employed; and lastly, the bricks must be set with great attention, that their surfaces may be perfectly parallel and perpendicular to the direction of gravity, for otherwise the wall composed of them, instead of being truly perpendicular, would lean over on one side and fall. We shall enter into some particulars on these points, but first we must describe the tools and materials used in Bricklaying.
The trowel is the first and most indispensable of these tools. It is a thin, flat, lozenge-shaped blade of steel, fixed into a handle. It is with the trowel the workman takes up and spreads the layer of mortar put between each brick, and with it he also cuts the bricks so as to fit into any corner, or to adapt them to some particular form; and to enable it to cut, or rather chip, such a hard substance as burnt clay, and yet not break, it is necessary that the blade should be of well-tempered hard steel. The square and level are made of wooden rules put together; the first at a true right angle, to enable the bricklayer to set out his walls correctly perpendicular to each other,—the second is framed like a ⟂, with a plummet hanging in a slit in the upright piece; now, as the two rules are correctly perpendicular to each other, it is clear that when the first is set by means of the plumb-line perpendicular to the horizon, the other will be truly horizontal. By means of this important instrument, the workman guides his work, so that the wall he is building shall be upright, and the courses of bricks composing it horizontal. By means of this important instrument, the workman guides his work, so that the wall he is building shall be upright, and the courses of bricks composing it horizontal.
Mortar is the name given to the composition with which the bricks are put together. Good mortar should be made of newly-burnt quicklime from grey limestone, and of clean river-sand, in the proportions of one-third lime to two-thirds sand. The lime is slaked by pouring a little clean water on it, and when it falls to powder by the chemical action, the sand is added gradually, and the whole well mixed up with a spade, more water being used till the mass is of the proper consistence for spreading easily. As the adhesion of the bricks depends on the mortar being applied before it begins to set or harden, it should not be mixed till it is to be used. When these simple precautions are attended to, the mortar becomes in time as hard as stone, and the brick-work constructed with it is nearly as indestructible. It was by taking this care with their materials that our forefathers built walls that have stood uninjured for centuries. In some of the cheap common buildings of the present day, mortar is too often made from lime which has been so long from the kiln, that it is nearly reconverted into a hydrate, and has lost the chemical quality which renders it valuable; the sand, too, is taken from the road with all its impurities, and the water from the nearest kennel. With such materials a mass of mortar is made, and suffered to stand for several days before it is used; the consequence is, that such buildings are neither safe nor durable.
The mortar is made up by an assistant, called a bricklayers’ labourer, and is taken by him to the spot where the workman wants it in what is called a hod: this utensil, which consists of three sides of a rectangular box fixed edgeways at the end of a long handle, is expressly contrived to be carried on the man’s shoulder, and leave his hands disengaged, to enable him thus loaded to ascend and descend a long ladder; the hod being held standing upright on the handle, the labourer can put bricks into it with his right hand, or another assistant fills it with mortar.