Figure 8-47.-Joint finishes.

at the bottom of the arch than at its top, but it should not narrow to less than 1/4 inch at any point. As laying progresses, make sure the arch does not bulge out of position.

Templet

It is obviously impossible to construct an arch without support from underneath. These temporary wooden supports must not only be able to support the masonry during construction but also provide the geometry necessary for the proper construction and appearance of the arch. Such supports are called templets.

DIMENSIONS. - Construct a brick arch over the templet (figure 8-49) that remains in place until the

Figure 8-48.-Common arch shapes.

mortar sets. You can obtain the templet dimensions from the construction drawings. For arches spanning up to 6 feet, use 3/4-inch plywood to make the templet. Cut two pieces to the proper curvature, and nail them to 2-by-4 spacers that provide a surface wide enough to support the brick.

POSITIONING. - Use wedges to hold the templet in position until the mortar hardens enough to make the arch self-supporting. Then drive out the wedges.

Layout

Lay out the arch carefully so that you don't have to cut any bricks. Use an odd number of bricks so that the key, or middle, brick falls into place at the exact arch center, or crown. The key, or middle, brick is the last one laid. To determine how many bricks an arch requires, lay the templet on its side on level ground and set a trial number of bricks around the curve. Adjust the number of bricks and the joint spacing (not less than 1/4-inch) until the key brick is at the exact center of the curve. Then, mark the positions of the bricks on the templet and use them as a guide when laying the brick.

Figure 8-49.-Using a template to construct an arch.