233. To build any kind of a brick structure so as to make a strong and durable piece of work, it is necessary to have a bed of some kind of mortar between the bricks. Brickwork, therefore, consists both of bricks and mortar, and the strength and durability of any piece of work will depend upon the quality of the bricks, the quality of the mortar, the way in which the bricks are laid and bonded and whether or not the bricks are laid wet or dry.
The kinds and qualities of mortars used for laying brickwork are described in Chapter IV (Outside Finish, Gutters, Shingle Roofs). The majority of the brick buildings in this country are built with common white lime mortar, to which natural cement is sometimes added. For brickwork below ground either hydraulic lime or cement mortar should be used. (See Sections 107 and 127.)
* Ira O. Baker, in "Masonry Construction," p. 38.
The function of the mortar in brickwork is threefold, viz.:
1. To keep out wet and changes in temperature by filling all crevices.
2. To unite the whole into one mass.
3. To form a cushion to take up any inequalities in the bricks and to distribute the pressure evenly.
The first object is best attained by grouting, or thoroughly "flushing" the work; the second depends largely upon the strength of the mortar, and the third is affected principally by the thickness of the joints.
Common brick should be laid in a bed of mortar at least 3/16 and not more than 3/8 of an inch thick, and every joint and space in the wall not occupied by other materials should be filled with mortar. The best way of specifying the thickness of the joint is by the height of eight courses of brick measured in the wall. This height should not exceed by more than 2 inches the height of eight courses of the same brick laid dry.
As common bricks are usually quite rough and uneven, it is not always easy to determine the thickness of a single joint, but the variation from the specifications in any eight courses that may be selected should be very slight. It is not uncommon to see joints \ inch thick in common brickwork, especially where the work is not superintended.
Pressed bricks, being usually quite true and smooth, can be laid with a 1/8-inch joint, and it is often so specified. A 3/16-inch joint is probably stronger, however, as it permits filling the joint better.