Concrete columns are often covered with caps. These caps are made by forming wooden molds and pouring in concrete, which dries into the shape of the cap. Many times these caps are purchased pre-molded from manufacturers. However, you can save money by making your own mold and casting your own concrete cap. You can make a concrete cap mold in six to eight hours, depending on the size and scope of the project.
Measure the column that is to receive the molded concrete cap. Generally, columns are 16-by-16 inches, which corresponds to one concrete block long and two concrete blocks wide. However, columns may vary in length and width.
Add five inches to the length and width of the column measurements to allow for cap overhang and 2-by-4 framing. Transfer the measurements onto 3/4-inch plywood. Square the measurements and snap a chalk line. Cut the plywood with a circular saw. For safety, wear a dust mask and safety goggles before proceeding to cut the plywood.
Cut 2-by-4 pieces that correspond to the length and width of the plywood. Subtract three inches from two of the 2-by-4s to account for the joins to the remaining two 2-by-4s. For example, if your measurements are 21-by-21 inches, you would normally cut four 2-by-4s 21 inches long. However, since you are constructing a box mold, you will place two of the 2-by-4s on two opposing sides and two 2-by-4s in between the first two to enclose the box.
Attach the 2-by-4s to the plywood with 3-inch screws. Connect the 2-by-4s at the corners with 3-inch screws. Grease the interior of the plywood box with Crisco to keep the concrete from sticking to the mold. Lay the mold with the 2-by-4s facing up and pour half of the mold full.
Add half-inch rebar on top of the concrete. Cut the rebar two inches shorter than the cap mold to prevent the rebar from being exposed after the molded concrete cap has dried. Make sure that the rebar is placed one inch from each side of the mold. Gently tap the side of the mold to remove bubbles from the concrete mixture. Continue to fill the mold to the top, and allow the concrete to set for 30 minutes. Smooth the concrete off with a concrete hand trowel, and allow the mixture to set for 24 hours. Turn the mold over, and tap the mold to remove the cap. Smooth the cap with sand paper to remove rough edges.