Concrete offers an alternative to other countertop materials such as granite, stone or marble. You can hire a local business to make and install concrete counters at about $75 to $150 per square foot, or you can take on the project yourself for a smaller cash outlay. Concrete counters are tough, durable and easy to clean.
Construct the Forms
A form contains the wet concrete, and is a mold sized to the counter's final dimensions. Make forms from melamine, which is slick enough to prevent concrete from sticking, but is sturdy enough to hold the heavy material. To aid release, wipe a small amount of olive oil or vegetable oil on the melamine. Hold the forms together with drywall screws. Caulk all the seams and corners between individual form pieces with a dark-colored latex caulk, which stands out against the white melamine surface so you are certain not to leave voids.
Choose a concrete mix formulated specifically for countertops. Many manufacturers blend and label bags of concrete specifically for counters. Add any coloring powders, then mix the concrete to an oatmeal consistency. A drier concrete mix produces a stronger finished product. Pour the wet concrete into the form, pressing it into place around the entire form so that no spaces remain. The bottom of the form is going to be the top of your counter. When the form is about half full, add wire mesh or similar metal for strength, then pour in the rest of the wet concrete. Use an orbital sander held against the outside of the form as a means of adding vibration that will both help the concrete settle and force out air bubbles. Screed the concrete by moving a long piece of wood across the top of the forms in a back-and-forth sawing motion.
Troweling and Curing
Trowel the concrete surface smooth. It will likely become wet as you do so, since some of the water will rise. Repeat the troweling process several times during the first few hours, but avoid overworking the concrete with each troweling. Since this is the bottom of the counter, and will not visible, it need not be perfectly smooth. Troweling helps keep any voids within the material filled and further releases air bubbles. Cover the concrete with plastic, which helps retain moisture in the material so it doesn't cure too fast and become brittle.
Polishing and Finishing
After several days -- or even a few weeks -- of curing, unscrew and disassemble the forms. Gently flip the concrete over and fill any voids in the countertop that may have appeared during curing. Sand any high spots as well. Sand the edges smooth, too. You can further color the counter with a blend of muriatic acid and dyes if you'd like. Then coat the tops and sides with a food-safe wax, such as carnuba. Buff the wax to a sheen. The counter is ready for installation. Make sure you mount the concrete atop cabinets made of at least 3/4-inch-thick plywood. Construction adhesive will hold the counter in place on its solid support.