Household items made from cement such as pavers, benches and countertops can be quite expensive to purchase. Many of these items are easy to complete by do-it-yourselfers, and most projects begin as poured pieces that harden in simple square or rectangular molds and are then assembled or laid into place. Constructing one of these uncomplicated molds requires only a few supplies and a little bit of time.
Decide how long and wide you want your finished cement slab, then determine how thick the finished concrete ought to be. Purchase pieces of lumber from your local home improvement or lumber store that is as long, wide, and thick as required for your particular mold. Make sure that two of your boards are at least 2 inches longer than the measurements for the finished slab, so you can attach the boards to each other.
Divide the excess length of the longer boards in half, and use a tape measure to measure this distance from either end of each long board. Mark these measurements with a pencil. These are the points of attachment.
Line up the short edge of one of the smaller boards with a pencil mark on one of the longer boards, ensuring that it is positioned lengthwise along the mark. Use a clamp to hold these two boards together. Sink a straight row of three to four carpentry nails along the back of the long board into the edge of the short board using your hammer.
Attach the second shorter board to the other pencil mark on this long board.
Position the remaining longer board so that the marks on it line up with the unattached short edges of the smaller boards. Clamp it into place. Hammer nails through the back of the long board into the edges of each shorter board, keeping your lines of nails as straight as possible.
Nail a sheet of plywood over one open side of the mold--if you are not pouring the cement onto a site, as with a sidewalk--so the molded cement can later be removed.