128. It is usual to build concrete walls, piers, arches, etc. by depositing the concrete in forms, or molds, made somewhat as follows: Posts of 4"x4", or 4" X 6" timber are set up in pairs on opposite sides of the wall where the blocks are to be formed, each pair being strongly bolted, to prevent springing. Against the inner sides of the uprights are laid planks, 1 1/2 or 2 inches thick, the distance from face to face of the boards being just the thickness of the wall. The planks frequently have beveled ridges formed on the inner side, to produce the appearance of joints in the wall. This is shown in Fig. 66, in which a represents the posts; b, the boarding; and c, the molded or beveled strips, which make the apparent joints when ashlar is to be imitated. It is evident that any kind of stone masonry may be simulated, by varying the position and shape of the strips or cleats.

Methods Of Construction Molds 193

Fig. 66.

It is recommended that the inside of the molds be washed with a solution of soap before laying concrete between them.

After the lower portion of the concrete wall has set, the bolts in the uprights are loosened enough to permit the withdrawal of the molding boards, which are put in place higher up. A movable cribbing is often used, consisting of slotted standards, which are raised, when necessary, without interfering with the work of laying the concrete.