This section is from the book "A Treatise On Architecture And Building Construction Vol2: Masonry. Carpentry. Joinery", by The Colliery Engineer Co. Also available from Amazon: A Treatise On Architecture And Building Construction.
201. The proper construction of a brick wall involves many things besides the mere laying of one brick on top of another, with a bed of mortar between. The manner of laying or bedding the bricks, and the general method of doing the work having been considered, we will next take up the points in construction required to obtain a strong and durable wall, and the precautions to be observed to prevent settlements and cracks, and to adapt the work to the purposes for which it is intended.
202. In bricklaying, all corners and joints should be carefully plumbed, the courses of brickwork kept perfectly horizontal - which necessitates uniform mortar joints - and the wall surfaces, both exterior and interior, must be kept in perfect alinement. All these conditions may have been complied with, and yet the work may be imperfect; the merit of the brickwork must be judged by the thoroughness of the bond observed in every portion of the wall, both lengthwise and crosswise. This bond must be maintained by having every course perfectly horizontal, both longitudinally and transversely, as well as perfectly plumb. Aside from the quality and character of the material, the bonding of a wall contributes most of its strength.
203. Bond, in brickwork, is the arrangement of the bricks adopted for tying all parts of the wall together by means of the weight resting on the bricks, as well as by the adhesion of the mortar; and also for distributing the effects of the weight over an increased area.
204. When the bricks are placed lengthwise on the face of the wall, as at a, in Fig. 75, they are termed stretchers; when placed crosswise and their ends only exposed to view in the face of the wall, as at b, they are called headers. A course means the thickness of a brick and a mortar joint.
205. To obtain the best results in bonding throughout the mass of the wall, strict attention must be given to the location of every joint in the brickwork. On the faces 2-8 of the wall, the vertical joints in each course throughout the height should be kept perpendicular, or directly over those in the second course below. This is called keeping the perpends. Unless the closest attention is paid, the lap is ultimately lost through irregularity of the brick and mortar joints, and extra bats, or closers, are necessary. The joints across the top of the wall should also be kept in line, so that if the perpends are observed on one face of the wall, the other face will also work up correctly. Even when the wall is exposed on only one face, it is just as essential to have the joints on top of the wall kept in line, as otherwise its effective longitudinal bond will soon be lost, since at best the heading bond furnishes a lap of only 2 inches.
206. The importance of having the bond in brickwork preserved in the whole wall can be understood by reference to Fig. 75, which represents a section of a wall consisting of alternate courses of stretchers and headers.
By the method of placing the brick as shown, no longitudinal bond exists, and the wall is simply a series of isolated piers which join each other at the vertical line c-d, and have no bond or union between them other than that obtained by the adhesion of the mortar.
This method manifestly lacks strength and efficiency. In order, therefore, to overcome this constructive difficulty, and secure a continuous bond in the length of the wall, recourse - is had to a different arrangement of the bricks and also to the use of blocks which vary in size from the ordinary brick.
207. These blocks are called closers, the term meaning that they perfectly finish or close the length of the courses which have been adjusted to obtain the bond. The vertical joint, which is shown at c-d, in Fig. 75, is avoided, and no two adjacent courses have joints which are immediately over each other. The closers are made by cutting the bricks with a smart blow with the edge of the steel trowel into such blocks as the situation requires. These are called bats and are designated according to the proportion which each bat bears to the whole brick. Pressed and enameled bricks are often cut with a cold chisel to get a more even fracture.
The different bats or closers used in brickwork are shown in Fig. 76; (a) represents a whole brick of the usual size, 8 1/4 in. X 4 in. X 2 1/4 in. When the brick is cut longitudinally, as at (b), on line a-b, each half is called a queen closer; but as it is difficult to cut the full length in this manner, the usual mode is to first cut the brick on the line c-d, and then cut each half on the line a-b. When the brick is cut as at (c), it is called a king closer, and is a form well adapted for closers at door and window jambs, etc. When one-fourth of the whole length of the brick is cut off, as at (d), the remainder is called a three-quarter bat; and in like manner the portion remaining, as at (e), is called a half bat; and at (f), a quarter bat.
208. In connection with the use of closers, whereby the lap is properly secured, there are several methods of placing the brick in the wall, each method having its own name to indicate the kind of bond used. A wall being considered as having the properties of a column, its bearing capacity will necessarily depend on the strength of its least dimension, which is its thickness, so that the bond which secures a thorough union of the constituent parts in this direction will always be the most desirable.