Concrete Countertops: The Design and Construction Process

accurately transferred the knockout measurements, caulk the sink knockout in its marked position. To install the faucet knockout, use a drill or a driver. Cheng says to remember that the larger disk will face the ceiling and will form the recess for the nut that will hold the faucet in place. Ready-made sink knockouts for popular sizes are available in stores. For a custom sink knockout, stack rigid-foam insulation sheets the desired thickness of the countertop and cut out the shape of the opening of the sink. Cheng says that the sink will come with a paper template showing its dimensions so DIY-ers can trace it as they cut the edges of the knockout. Ready-made faucet knockouts are also available in popular sizes, but for a custom faucet knockout, stack a one-and-three-eighths of an inch disk of plywood or foam on one that is two-and-seven-eighths inches in diameter. Tape the smaller disk atop the bigger one. Cheng suggests wrapping the knockouts with thin packing foam and packing tape so that pulling the knockouts from the concrete mold will be easier. Innovative DIY-ers can create soap dishes and affix drain knockouts by using a Masonite hardboard for the soap dish and placing a wood dowel cut in half from the soap dish to the sink knockout, which will serve as an affix drain. Finishing the Mold To avoid wasting material, use the remaining Melamine from the base to cut sidepieces, which will serve as walls for the mold. Cut two, three-and-one-fourth inch-wide sidepieces and two, two-inch-wide backers that will form an “L” shape to support the walls when the concrete when is poured. Attach the sidepieces to the baseboard by drilling drywall screws into the edge of the baseboard. Repeat to attach the other sidepieces. To secure the walls, attach the L-shaped Melamine pieces. Cheng says to use one-and-one-half-inch-long screws because the tips of longer screws could pop through the side of the mold. Next, use blue painter’s tape to mask all the joints of the mold, keeping the edge of the tape one-eighth of an inch back from both sides of the joint. Squeeze a fourth-of-an-inch bead of caulk evenly around the mold. Cheng says that tilting the tip of the caulk gun to a 45-degree angle with help the flow and make for smoother application of the caulk. Use a wetted finger to smooth the caulk at the joints. Be careful not to push down too hard. Then, peel the tape while the caulk is still wet and let the silicone form for several hours. Photo by Fu-Tung Cheng for Taunton Press in Concrete Countertops Made Simple To strengthen the countertop, Cheng suggests installing steel reinforcements to the mold. Depending on the length of the countertop, lace strips of rebar together to form a truss around the perimeter of the mold. When installing wire mesh, make sure to clip out knockout dimensions before securing the end of the wire over the walls of the mold on to the melamine board with drywall nails. Pouring the Concrete To make the concrete mix, Cheng suggests buying high-strength, 5,000-pounds-per-square-inch bagged concrete like Sakrete’s 5000 Plus Concrete. A safe concrete mixture comprised of Portland cement (the most common type of cement mix), sand and gravel, Sakrete 5000 Plus Concrete costs approximately $5.00 for a 50-pound bag. Cheng says four to six sacks will be needed to complete a concrete countertop. After assembling all the materials and tools needed to mix the concrete, wear a dust mask and gloves and pour the concrete mix and admixtures into the mixer. Admixtures often comprise of coloring, decorative aggregate (mixed stones) and fibers to embellish and strengthen the countertop. To avoid a dust invasion, secure a piece of plastic with a bungee cord over the opening of the mixer. Once the mixer has evenly distributed the concrete, add the amount of water recommended on the bag of concrete mix and let the mixer run for several minutes. “The mix may first appear lumpy and dry, but don’t be tempted to add lots of water right away,” says Cheng. Concrete with too much water in the mix will crack and shrink as it is left out to dry. After making sure that that clumps are broken up, let the concrete rest for two minutes and then continue running the mixer. After about 10 to 15 minutes, Cheng says that the concrete should be the consistency of runny oatmeal. Recruit a helper to pour the concrete mix into the mold. Use gloved hands to spread the concrete evenly into the steel reinforcements and around the knockouts. Make sure that no concrete covers the sink knockout. When the mold is about two-thirds full, work the vibrator back and forth beneath the surface of the mold for several minutes. When the mold is slightly overfull, jiggle the pour table to help settle the concrete. Smooth the surface of the mixture by applying a steady downward sawing motion with a two-by-four piece of wood. After pushing the excess concrete off the table, glide a steel concrete trowel across the surface of the concrete using the excess concrete. Leave the concrete to cure, or form, in a warm, humid environment between 60 to 90 degrees with 25 percent or greater humidity. Removing the Countertop from the Mold Begin by removing the L-shaped Melamine braces that supported the walls of the mold and take out every screw that held the mold together. Next, carefully pry out the faucet knockout, avoiding direct contact with the concrete. Then, round the edges with a file. Repeat the filing process for the other edges of the countertop. In order to remove the base Melamine board from the bottom of the countertop, gather helpers (who should be wearing gloves) and place some foam cushion blocks where the countertop will be placed when flipped over. Cheng suggests flipping the countertop in two steps; first, by flipping it into a vertical position before allowing it to land on its backside on the foam blocks. Once the Melamine baseboard is removed, pry out the rest of the knockouts. Use a single-edge razor to scrape away the caulk or excess concrete that’s covering knockouts. Leave the countertop to cure again for two to three days in the same humid conditions as before. Cheng says that the longer the curing period, the harder the concrete will get. Polishing and Slurrying Polishing the surface will eliminate blemishes and emphasize the fine sand and any decorative aggregate from the admixture, according to Cheng. Use a diamond disk mounted on a variable-speed polisher to polish the surface. After polishing the entire surface, fill any holes that appear on the surface of the countertop with slurry. Wet the countertop with water and apply the slurry to the surface using a putty knife. Scrape off any excess slurry and let the countertop cure for another two days. Sealing and Waxing Since concrete is a naturally porous material, seal and wax the surface to make the countertop stain-resistant. Topical sealers are resistant to stains but tend to scratch and peel. In order to remove a topical sealer, noxious chemicals must be used, which could be a health hazard. Cheng suggests using a water-based acrylic penetrating sealer instead, which is the most food-safe penetrating  sealer but will leave the countertop susceptible to such acid stains as lemon juice, wine and vinegar. Cleaning and recoating the countertop can remove these stains. Before applying the sealer, make sure the countertop is clean. Swirl the sealer, which has been diluted with water in a 50:50 ratio, in circular motions on to the countertop. Repeat the process with undiluted sealer. When the entire surface of the countertop is covered, wipe off the excess sealer with a clean rag. Use a clean cloth or towel to apply the wax on to the countertop surface in circular motions. Wipe off all the excess wax to avoid leaving streaks. After letting the wax dry for two to three minutes, apply the polish to the countertop using a clean cloth. Installation Make sure that the counter or cabinet that will support the countertop has proper reinforcements to support the hundred-something pounds of concrete. Reinforcements can be made by adding vertical and horizontal plywood behind and underneath the counter space or by adding detachable feet to the bottom of the counter or cabinet. Recruit some helpers again. Carefully plan the path from the workstation to the counter or cabinet where the countertop will be installed. “Get furniture and other obstacles out of the way, and talk about any potential trouble spots,” says Cheng. He also suggests using a dolly padded with carpeting to transport the countertop through your house. After the countertop has been installed, clean up the area and take a rest. While this project may take a little longer than other DIY projects, Cheng says that in the end, “it’s about having fun.” For more information about concrete countertops, read here.

...Continued - Page 3 of 3 ( 1 2 3 )
< Previous Page