The Methods of Joining Stone.

As the strength and durability of masonry depend as much on the method employed, and the care taken in making all the joints to correspond accurately with each other, as in the quality of the material employed, some remarks will be required in explanation of the methods of joining stone. We shall, therefore, enumerate the several means adopted by workmen, and, where necessary, notice the purposes to which each method is best adapted, giving some cautions to secure success in practice, and to save the workman unnecessary labor and trouble.

The joints in masonry are either secured by the means of mortar, cement, or plaster of Paris, or the courses are held together by cramps, joggles, mortice, and tenoning, or dovetailing.

1. Joining by mortar, or cements. It is absolutely necessary that the joints should be perfectly smooth, and touch in every part; and the stones must be so square as to bed well on each other, that is to say, they must not have such irregular faces as to roll, or, in technical terms, be winding to each other. The greatest care must be taken by the workman to have his mortar of a proper consistence-not too thin, as in drying it would shrink from the work, nor too thick, for that would prevent the stones from bedding properly. The best way in irregular masonry, or in that composed of small stones thrown, as it were, between the regular work, as in compound masonry, is to saturate fresh lime with water, and, while hot, to pour it on the work, which hardens and consolidates the whole into one solid mass. This method is much used in joining soft stones and brickwork, and is calculated to promote the strength and solidity of the work.

2. Joining by cramps. Cramping is performed by inserting into the two pieces of stone, which are to be bound together, a piece of iron or some other metal, the ends of which, bent at right angles, are inserted in a cavity cut in each stone, the cavities being so large as to admit the iron easily; melted lead is then poured in to fill the vacant space, and, when cold, a chisel is driven into it, so that it may press close to the work; for all metals expand by fusion, and obstacles may prevent them from contracting in cooling. Cramps composed of copper are, in many cases, very preferable to those made of iron, for they are less likely to oxidize, or rust, or to be affected by the lime or mortar. It would be of advantage to coat the cramps, if made of iron, with some substance that would defend them from the effects of damp. We may here remark, that the channel made to receive the cramp should be dovetailed, to prevent the lead from coming out, which it is otherwise apt to do, in the course of time. The only objection to the use of copper cramps, in preference to iron, is their expense, which in large public works is not of any importance, and, for common purposes, iron answers very well; but the more malleable or tough the iron

the better it is, as it is more calculated to resist the different temperatures to which the work may be exposed.

3. Joining by joggles. The method of securing the joints of masonry by means of joggles is chiefly adopted for securing the joints of columns or pillars; and consists in sinking a cavity in the two pieces in such a manner as to make them correspond with each other, and inserting in that cavity a piece of metal, stone, or even wood, so that any lateral thrust may not be able to separate them. This method may, with very great advantage, be applied in the construction of domes, and works of the same nature, where it is necessary to avoid the lateral thrust as much as possible.

We

:

e may here take the opportunity of mentioning a plan proposed by Dr. Hutton, in his edition of Oznamare's Mathematical Recreations, for taking away the lateral thrust of domes and cupolas. The following is the problem proposed, and the solution given:

How to construct a hemispherical arch, or what the architects call an arc en cul-de-four, which shall have no thrust on its piers.

“Let A B, fig. 8, be two contiguous voussoirs, which we will suppose to be three feet in length, and eighteen inches in breadth. Cut out on the contig

uous

indes two cavities,

in the form of a dovetail, four inches in depth, with an aperture of the same extent, a, b, five or six

Fig. 9.

inches in length, and as much in breadth. This cavity will serve to receive a double key of cast-iron, as shown in fig. 9, or of common forged-iron, which is still more secure, as it is not so brittle. These two voussoirs will thus be connected together in such a manner that they cannot be separated without breaking the dovetail at the re-entering angle; but, as each of its dimensions in this place will be four inches, it will be easily seen that an immense force would be required to produce that effect; for we are taught, by well-known experiments on the strength of iron, that it requires a force of four thousand five hundred pounds to break a bar of forged iron an inch square, by the arm of a lever of six inches; consequently, two hundred and eighty-eight thousand pounds would be necessary to break a bar of sixteen square inches, like that in question. Hence there is reason to conclude, that these voussoirs will be connected together by a force of two hundred and eighty-eight thousand pounds; and as they will never experience an effort to disjoin them nearly so great, as might easily be proved by calculation, it follows that they may be considered as one piece."

They might be still further strengthened in a very considerable degree, for the height of these dovetails might be made double, and

a cavity might be cut in the middle of the bed of the upper voussoir, fit to receive it entirely: the dovetail could not then be broken without breaking the upper voussoir also; but it may be easily seen that, to produce this effect, an immense force would be required.

The second method proposed by Dr. Hutton is more properly by

9.999

a

Fig. 10.

с

the aid of joggles. Let A and B, fig. 10, be two contiguous voussoirs, and C, fig. 11, the inverted voussoir of the next course, which ought to cover the

joint between A and B. Each of the voussoirs A and B being

Fig. 11.

divided into two parts, as ab and cd; then if at a banded we sink an hemispherical cavity, in which to introduce a globe of very hard marble, and in the upper voussoir, fig. 10, we sink similar cavities, be; this, when laid on bc, fig. 11, will form a secure joint without any lateral thrust; and the two courses cannot be separated without a force adequate to either break the solid stone, or disunite the marble globe; à force almost inconceivable, or at least one far superior to that produced by the arch; the whole dome, or cupola, is, in fact, one solid mass, and can exert no lateral thrust upon the walls on which it is raised. Marble globes are recommended, because iron is liable to rust; but, if the joggles were made of iron, and covered with pitch before they were placed in the cavities, there would be little to fear from rust; and particularly as the iron is inclosed in the substance of the stone, and quite excluded from the

Little need ho action of atmospheric causes.

said in this place as to morticing and tenoning, or dovetailing, except that they differ slightly from the same operations in joiners' work; for, as cement is used in the joining, they need not be so accurately cut, and are made shorter and thicker than those formed by the joiner, it being sufficient that the parts of each piece to be joined enter into each other at most five or six inches, even in large masses of stone. In small pieces, an inch or an inch and a half is sufficient; for, if the tenon or dovetail be too long, it will decrease the solidity of the joint. For greater security, a small channel is frequently cut in the shoulder of the joint, and melted lead is poured into it, which, filling up the space round the tenon or dovetail, makes the joint more secure, and the work firm and solid.

In laying some sorts of stones, it is desirable, as far as possible, to place them in the same direction as they had when in the quarry, or, as it is termed by workmen, bedways of the stone; for, if laid in other directions, they are liable to peel and split by the action of the atmosphere.

BRICKLAYING.

Foundations.

The best soils for building upon are gravel, chalk, and stone rock.

Those most to be guarded against are sands, bog earth, clays, and made earth (no matter how hard). Where these occur, avoid piling (except in water works); plank the foundations through the centre of the walls, place long tassels in the piers, lay in chain bond, let the plates be stout, and in one piece, the whole length of each wall; all that is required is to so bind the building that it may settle altogether, and not partially.

In doubtful foundations, it is advisable to have a trench dug out to the depth of 2 feet to 3 feet below the footings of the brickwork, and about twice the width of the footings, which is to be filled up with concrete, composed of stone lime ground and ballast, or coarse gravel, to be mixed with water, in the proportion of one of lime to five or six of gravel; immediately that it is made up it must be shot into the trench from a stage, 6 feet above, which will cause it to fall in a solid mass; and in a few hours afterwards it will be as firm as a rock.

It is strongly recommended to have good plates; whatever may be slighted in other parts these should not be neglected—they are the soul and support of a building, and cannot, if put in too sinall, be taken out and replaced, as other timbers may; the difference in large houses will rarely amount to twenty-five dollars.

Bond the work-English bond-using all whole bricks, a course of stretchers and headers alternately.

Particular care must be taken that all the internal joints of brickwork are well flushed up with mortar; too frequently the workmen are apt to neglect doing it; the consequence is, that all the interior joints are hollow, and allow the damp to penetrate to the inside, no matter how thick the wall may be. Another serious defect in brickwork is in not properly bonding the facing to the backing, particularly if the facing be malms or bricks, which cost an extra price; generally the headers are only bats or half bricks, instead of being a stretcher or a whole brick to bond in with the brickwork at the back; there ought to be at least one stretcher in every 3 feet to each course, if there be not the wall will split or divide into two thicknesses.

In building arches of a large span, it is advisable to build them in half brick rims, with vertical or radiating bond every 3 or 4 feet in the girt; if this latter precaution be not adopted, the consequence will be, that when the centre is struck, the rims will divide and weaken the arch, and perhaps cause a total failure.

In selecting bricks, clap them together-if they ring well, and,

when broken, show that they are burnt through, they will answer the purpose. A hard clamp burnt gray stock is all that is wanted for strength; for water-works and foundations use clinker burnt marl stocks. Avoid samnel or place bricks, and chuffy stocks, and generally prefer hand tempering to pugging the clay.

In mixing of mortar, it is advisable to see that the laborer properly turns up the mortar, and that the lime is thoroughly incorporated with the sand throughout; avoid using too much water, as it drowns the linie and weakens it; in large works it is best to mix the lime and sand in a mill-cement must be mixed in small quantities.

TABLE

Showing the Quantity of Earth to be removed, the Number of Bricks and Gallons in one foot in depth or length.