They are generally built either of brick or stone, and will be considered more in detail under the heads of "Brickwork " and "Masonry" respectively. The following points, however, should be attended to in walls of every description: -
The whole of the walling of a building should be carried up simultaneously; no part should be allowed to rise more than about 3 feet above the rest,2 otherwise the portion first built will settle down and come to its bearings before the other is attached to it, and then the settlement which takes place in the newer portion will cause a rupture, and cracks will appear in the structure. If it should be necessary to carry up one part of a wall before the other, the end of the portion first built should be "racked back " - that is, left in steps, each course projecting farther than the one above it.
Work should not be hurried unless done in cement, but given time to take its bearings gradually.
New work built in mortar should never be bonded to old, until the former has quite settled down. Then bonds may be inserted if required.
As a rule, it is better that the new work should butt against the old, either with a straight joint visible on the face, or let into a chase,3 so that the straight joint may not show; but if it be necessary to bond them together, the new work should be built in a quick-setting cement, and each part of it allowed to harden before being weighted.
Even after walls are completed, they are likely to crack if unequally loaded.
The walls of a building are as a rule vertical, in which case each course should be laid level in every direction. In inclined or "battering" walls the courses should be at right angles to the pressure upon them.
Bond4 is an arrangement of bricks or stones placed in juxtaposition, so as to prevent the vertical joint between any two bricks or stones falling into a continuous straight line with that between any other two.
1 Sc. Dykes. 2 A scaffold height is sometimes made the limit.
3 Sometimes called a slip joint. 4 Sc. Band.
This is called "breaking joint," and when it is not properly carried out - that is, when two or more joints do fall into the same line, as at x y - they form what is called a straight joint.
Straight joints split up and weaken the part of the wall in which they occur, and should therefore be avoided.
A good bond breaks the vertical joints both in the length and thickness of the wall, giving the bricks or stones a good lap over one another in both directions, so as to afford as much hold as possible between the different parts of the wall.
A further effect of the bond is to distribute the pressure which comes upon each brick over a large number of bricks below it. Thus in Fig. I there is a proper bond among the bricks forming the face of the wall, and the pressure upon the brick A is communicated to every brick within the triangle ABC.
A defective bond, either in brickwork or masonry, may look very well upon the face, as in Fig. 1, where the bricks regularly break joint vertically, but in which there is no bond whatever across the thickness of the wall, which it will be seen is really composed of two distinct slices of brickwork, each 4 1/2 inches thick, and having no connection with one another, except that afforded by the mortar.
To avoid this defect, the bricks or stones forming a wall are not all laid in the same direction as in Fig. 1, but some are laid parallel to the length of the wall, and others at right angles to them, so that the length of one of the latter overlaps the width of two below it.
Headersl are bricks or stones whose lengths lie across the thickness of the wall, the ends (or "heads ") of those in thin walls, or in the outsides of thick walls, being visible on the face and back.
Stretchers1 are bricks or stones which lie parallel to the length of the wall, those in the exterior of the work showing one side in the face of the wall.
It is most important that the construction of a wall should be uniform throughout, or that care should be taken, by using quick-setting cement, to prevent the unequal settlement that will otherwise take place. The evils caused by neglecting these precautions will be more fully entered upon in the Advanced Course, Part II.
1 Some consider these names as peculiar to brickwork; they are often used, however, in masonry, for stones placed as described. Sc. for "Header" and "Stretcher" in masonry is Inbond and Outbond.
The bricks or stones used for walling or arches should be well wetted before use, not only to remove the dust which would prevent the mortar from adhering, but also to prevent the bricks or stones from absorbing the moisture from the mortar too quickly.
In building upon old or dry work, the upper surface should be swept clean and wetted before the mortar is spread upon it to form the bed for the new work.
Neither brickwork nor masonry should ever be carried on while frost exists, or when it is likely to occur before the mortar is set.
If it is necessary to go on with the work at such a time, it must be covered up with straw or boards every night.