A.Jay Meunier responds: Sometimes Styrofoam is used for forming pockets in complicated areas because it's so easy to shape. But it's fairly costly and has to be handled very carefully when you remove it from the formwork if you plan to use it a second time. A simple, inexpensive way to form your brick shelf is with 2x4s and 1/2-inch plywood (see illustration, below). Make a short "wall" with a top and bottom plate and uprights every 18 to 24 inches and skin it with the plywood. It's easiest to build the shelf form separately, then nail it into place as the forms are set.
Unless you have design or loading requirements necessitating a 6-inch stem in your wall, an 8-inch wall will work fine to carry a 4-inch brick shelf. The 4-inch stem makes it a little more cumbersome to place concrete in the wall, especially if it contains a mat of rebar, so plan on the pour taking a little longer than usual. When placing the...
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