A pour-in-place concrete countertop can seem like an intimidating project for do-it-yourselfers considering the amount of physical labor. The steps are simple to follow despite the difficulty of the task, and the most challenging part for those who are unused to working with concrete will be the mixing and application of the concrete into the countertop mold. Wear rubber gloves, safety glasses, a long sleeve shirt and jeans to protect your skin from exposure to the concrete mixture and don't let a lack of experience discourage you from taking on the challenge of making your own pour-in-place concrete countertop.
Create the Mold
Cut a piece of melamine that is the length and width you want your countertop. This will become the base of your mold and will remain in place once the rest of the mold is removed. Nail or screw the board into place on top of your cabinets.
Cut strips of melamine to become the sides and front of your mold (the back wall will form the back of the mold). Each strip should be the intended height of the thickness of your countertop. Nail each strip to the base of the mold with a nail gun. Use nails approximately 1/2 inch longer than the thickness of the melamine. Longer nails might be different to remove and shorter nails may not be strong enough to hold the concrete.
Apply a 1/4-inch bead of caulk to the edges inside the melamine mold to prevent leaks and to give a curved appearance to the edges of your concrete countertop. Use a wet a rag over your finger to smooth the caulk along the edges of the mold.
Set reinforcing steel mesh into the melamine mold to ensure the integrity of the concrete countertop and to prevent cracks when the concrete dries. Keep the mesh no more than one inch from the area that will be the top of the countertop.
Create the Countertop
Combine the water, colorant and concrete mix in a mixing tub. The amount of each ingredient will depend on the size of your concrete countertop, but proportions will be noted on the concrete mix container. Stir the mixture with a mason's hoe until it has a consistency similar to cookie dough.
Scoop the concrete mixture into the melamine mold. Use a wood float to compress the concrete as you shovel it into the mold to prevent air bubbles that will weaken the integrity of the countertop. Use a hammer to lightly tap around the perimeter of the mold in order to break any air bubbles that accumulate near the mold's edges.
Allow the concrete to set for one hour, then use a trowel to scrape away any excess concrete from the top of the melamine mold.
Pry the melamine sides away from the countertop with a pry bar after it has dried for seven days. Pry against the melamine, not against the concrete, in order to avoid damaging the countertop.
Apply silicon sealant against the edges of the countertop where it touches the wall and around the bottom edges of the countertop where it touches the cabinet.
Apply concrete sealer on the top and edges of the concrete countertop to protect its surface.