BRICK MASONRY Many of the terms employed in stone masonry, and of the directions for properly doing the work, are equally applicable to brick masonry, aria therefore will not be here repeated. The follow ing sections will be devoted to those terms and specifications which arc applicable only to brick masonry.
150. Bonding Used in Brick Masonry. Some of the principles involved in the effect of bonding on the strength of a wall, have al ready been discussed under "Stone Masonry." The other considera tion is that of architectural appearance. The common method of bonding (Fig. 35) is to lay five or six courses of brick entirely as stretchers, then a course of brick will be laid entirely as headers. There is probably some economy in the work required of a brick layer in following this policy. The so-called English Bond (Fig. 36) consists of alternate courses of headers and stretchers. If the face bricks are of better quality than those used in the backing of the wall, this system means that one-half the face area of the wall consists of headers; certainly not an economical way of using the facing brick. The Flemish Bond (Fig. 37) employs alternate headers and stretchers in each course, and also disposes of the vertical joints so that there is a definite pattern in the joints, which has a pleasing architectural effect.
151. Constructive Feature's. On account of the comparatively high absorptive power of brick, it is especially necessary that they shall be thoroughly soaked with water before being laid in the wall.
An excess of water can do no harm, and will further insure the bricks being clean from dust, which would affect the adhesion of the mortar. It is also important that the brick shall be laid with what is called a shove joint. This term is even put in specifications, and has a definite meaning to masons. It means that after laying the mortar for the bed-joints, a brick is placed with its edge projecting somewhat over that of the lower brick, and is then pressed clown into the mortar, and, while still being pressed clown, is shoved into its proper position. In this way is obtained a proper adhesion between the mortar and the brick.
The thickness of the mortar joint should not be over one-half inch; one-fourth inch. or even less, is far better, since it gives stronger masonry. It requires more care to make thin joints than thick joints, and therefore it is very difficult to obtain thin joints when masons are paid by piecework. Pressed brick fronts are laid with joints of one-eighth inch or even less, but this is considered high grade work and is paid for accordingly.
152. Strength of Brickwork. As previously stated with respect to stone masonry, the strength of brick masonry is largely dependen upon the strength of the mortar; but, unlike stone masonry, the strength of brick masonry is, in a much larger proportion, dependent on the strength .of the brick composing it. The ultimate strength of brick masonry has been determined by a series of tests, to vary from 1,000 to 2,000 pounds per square inch, using lime mortar; and from 1,500 to 3,000 pounds per square inch, using cement mortar—the variation in each group (for the same kind of mortar) depending on the quality of the brick. A large factor of safety, perhaps 10, should be used with such figures.
153. Methods of Measuring Brickwork. There is unfortunate ly a considerable variation in the methods of measuring brickwork, the variation depending on local trade customs. Brickwork is often paid for by the perch. The volume of a- perch was originally taken from a similar volume of stone masonry, the unit being a section of the wall one rod feet) long and one foot high. Since the usual custom made such a wall 18 inches thick, the volume 24 cubic feet came to be considered as one perch of masonry; then this number was modified to the round number 25 cubic feet, for convenience of computation. The construction of walls one foot thick and with the same face unit of measurement, gave rise to a unit volume of cubic feet, which was also called a perch. Such units have un doubtedly arisen from the fact that it requires more work per cubic yard to build a thin wall than a thick wall, and the brick mason desires a. unit of measurement more nearly in accordance with the labor involved.