This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
To perform the operation of erecting a brick building it is necessary to lay the carefully chosen bricks upon each other, with a bed of some kind of mortar between. Ordinary brickwork is laid in common white lime mortar, but for greater strength and durability there is often added a proportion of cement, and for brickwork below ground, cement mortar only should be used. The thickness of the joints will vary from three-sixteenths of an inch to three-eighths of an inch, according to whether the joint is to be concealed or made a feature of the work.
The laying of the bricks should be carefully watched, as there is a tendency on the part of many masons to slight this work. " Bricks should not be merely laid, but every one should be rubbed and pressed down in such a manner as to force the mortar into the pores of the bricks, and produce the maximum adhesion; with quick-setting cement this is still more important than with lime mortar. For the best work it is specified that the brick shall be laid with a 'shove-joint,' that is, that the brick shall first be laid so as to project over the one below, and be pressed into the mortar, and then be shoved into its final position. Bricks should be laid in full beds of mortar, filling end and side joints in one operation. This operation is simple and easy with skillful masons, if they will do it, but it requires persistence to get it accomplished. Masons have a habit of laying bricks in a bed of mortar, leaving the vertical joints to take care of themselves, throwing a little mortar over the top beds and giving a sweep with the trowel which more or less disguises the open joint below. They also have a way after mortar has been sufficiently applied to the top bed of brick, to draw the point of their trowel through it, making an open channel with only a sharp ridge of mortar on each side (and generally throwing some of it overboard . so that if the succeeding brick is taken up, it will show a clear hollow, free from mortar, through the bed. ' This enables them to bed the next brick with more facility, and avoid pressure upon it to obtain the requisite thickness of joint. Neglect in wetting the brick before use is the cause of many of the failures of brickwork. Bricks have a great avidity for water, and if the mortar is stiff and the bricks dry. they will absorb the water so rapidly that the mortar will not set properly, and will crumble in the fingers when dry.
"Mortar is sometimes made so thin that the brick will not absorb all the water. This practice is objectionable; it interferes with the setting of the mortar, and particularly with the adhesion of the mortar to the brick. Watery mortar also contracts excessively in drying (if it ever does dry), which causes undue settlement and, possibly, cracks or distortion. The bricks should not be wetted to the point of saturation, or they will be incapable of absorbing any of the moisture from the mortar, and the adhesion between the brick and mortar will be weak. The common method of wetting brick by throwing water from buckets or spraying with a hose over a large pile is deceptive, the water reaches a few bricks on one or more sides and escapes many. Immersion of the brick for from three to eight minutes, depending upon its quality, is the only sure method to avert the evil consequences of using dry or partially wetted brick. Strict attention must be paid to have the starting course level, for the bricks being of equal thickness throughout, the slightest irregularity or incorrectness in it will be carried into the superposed courses, and can only be rectified by using a greater or less quantity of mortar in one part or another, a course which is injurious to the work. A common but improper method of building thick brick walls is to lay up the outer stretcher courses between the header courses, and then to throw mortar into the trough thus formed, making it semifluid by the addition of a large dose of water, then throwing in the brickbats (sand and rubbish are often substituted for bricks), allowing them to find their own bearing; when the trough is filled, it is plastered over with stiff mortar, and the header course laid and the operation repeated. This practice may have some advantage in celerity in executing work, but none in strength or security."
A modification of this practice, where the bricks are laid dry and grouted with moderately thin mortar in every course, may be successfully used in weather when there is no danger of freezing, and will make solid work. This is especially so for footings and foundations of brick where it is necessary that every joint shall be filled, as the thin grouting is more to be depended upon to fill every joint than the average mason
For inside walls which are to be plastered or otherwise concealed, the joints may be simply cut off flush with the trowel, but where the walls are exposed, the joints should be "struck." (Fig. 105.) This consists in pressing or striking back with the trowel, the upper portion of the joint while the mortar is soft, so as to form a sloping surface from the bottom to the top. "Keyed joints" are formed by running an iron jointer with round or V-shaped edge along the center of the flush joint, giving it a depression and hardening the mortar by the pressure. (Fig. 106.) Ruled joints are made by holding a straight-edge under the joint and running the jointer along, making a perfectly straight joint.