The construction is more or less well finished according as the facing is to be visible or not, but the principles on which building is based do not change. These principles are: to raise the wall perfectly perpendicular, and to interrupt the joins as much as possible both in the height and thickness of the wall.

Bricks are arranged endways and lengthways, that is to say, that their length is sometimes perpendicular, sometimes parallel to the direction of the walls. This arrangement is intended to avoid the continuity of the vertical joins in two consecutive rows; this interruption should be frequent in the upright joins.

It will be understood that there are many possible ways of combining the ends and sides; and this allows of varied designs being made by the use of bricks of different colours. We must, however, reject every combination which does not satisfy the above-mentioned conditions. It is beyond the province of this work to examine in detail every method used, and we will merely mention (Figs. 332 to 335) the most common ways of building a wall whose thickness is the length of one brick.

Fig. 332.

Fig. 333.

Fig. 334.

Fig. 335.

Figs. 332 to 335. Various Systems of Wall-building.

In thicker walls, the possible arrangements of the bricks are infinite, and we must choose those which give the best cohesion in each direction by interrupting the joins as much as possible. If the thickness of the wall allows of it, we begin by erecting two facings, and fill the hollow with bricks placed endways; then, every five or six layers, we place two layers of bricks diagonally and crossed, thus ensuring great cohesion.

To build a wall, we begin by erecting the two corners, quite vertically to the height of a few layers; then, between these two angles, we stretch a cord horizontally above the first layer. We place the bricks on a bed of mortar, and then press upon them with the hand while giving them a slight up-and-down motion so as to compress the mortar to its least thickness. Bricklayers generally effect this by striking the bricks with the edge of their trowel, but this will only do for facings; for insides the other method is more rapid. The upper edge of the bricks should follow the cord exactly. If their thickness is not uniform, the thickest ones are pushed down on to the mortar so that the upper surface of the row may be level and horizontal. The masonry is completed throughout the thickness of the wall, and when the layer is finished, the cord is raised to the height of the next, and the work continues.

The thickness of the joins naturally depends upon the fineness of the mortar, the uniformity of the bricks, and the thickness of the wall. With cement and well-pressed bricks we may succeed in making joins of only .002 to .003 (about 1/10th inch), with very fine mortar .006 to .007 (1/4 in.), and in ordinary brick-masonry from .012 to .015 (about 1/2 in.).

The bricks being always spongy, it is better to water them all together before they are used, as otherwise they will absorb some of the water of the mortar.

## Finishing The Joins

When the masonry is completed, we proceed to finish off the joins. . In high-class work, when the brick is visible, its fine red colour is brought out by washing it with dilute.hydrochloric acid; in this way all the stains of mortar or other substances are removed. Then the joins are hollowed out to a depth of half an inch or so with a special iron hook, cleaned, brushed, and sprinkled with water, after which a specially prepared fine mortar is introduced with a little pointed trowel. When this has become fixed, it is pressed with a polisher to smooth its surface. If fancy joins are required, they are cut in hollow or relief with a special iron tool. Hollow joins are, as regards durability, to be preferred to the projecting so-called "English" joins. More variety may be given to the general appearance by colouring the mortar used.

## Arches

The construction of arches of brick may be as much varied as that of walls; the same precautions must be observed for the joins, which must be perpendicular to the surfaces of intrados. In this way each part of the arch forms a corner, and the whole can keep in position without mortar.

When the thickness of the arch does not exceed the length of a brick or a brick and a half, it is built as an ordinary wall, the intrados being dressed either with endway or lengthway bricks alone, or with endway and lengthway bricks, the choice of arrangement being subordinated to the solidity of the whole. If the thickness is greater, several methods can be used; for instance, several arches each of the thickness of a brick or a brick and a half may be arranged, independent and one over the other. In England a series of superimposed arches each of one brick sideways is preferred, whatever be the thickness.

When the extrados of the arches remain visible after their construction, the dressing must be carefully done; for that purpose the position of the joins, according to the thickness of the bricks and the system chosen, is marked out on the semicircle, bearing in mind that there must be an odd number of layers, on account of the one serving as keystone.

The edges of the bricks being placed normal to the intrados, it follows that the join is thicker at the extrados than at the intrados. It is to avoid this inconvenience that bricks called "corner" and "knife-edge" are made (Figs. 235, 236).

The dressing of special arches, vaulted, annular, conical, spherical, cloister, etc., presents no great difficulty.

Flooring arches are generally made of hollow bricks, and the dressing of them is quite simple.