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How to Build and Install a Concrete Countertop (page 3 of 3)

Learn how to design, build and install a beautiful concrete countertop.

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Step 7: Remove the Mold

Remove the sides of the mold from the concrete first, being careful not to press against the concrete. Cut the wire that was suspending the rebar or steel mesh as close to the surface of the concrete as possible. Remove the screws attaching the sides of the mold to the bottom and use a pry bar and a hammer to gently pry the mold apart. Again, be careful not to press the pry bar or hammer against the concrete.

When the sides of the mold are off, flip the concrete countertop over to expose the surface – this is a two-person job (Image 1). Have one person push the concrete to one end of the table while the other person flips it over and the first person gently lowers it into place.

flipping concrete out of mold is a two person job

Step 8: Clean, Sand and Seal the Countertop

Clean the concrete with a mixture of 10 parts water to 1 part muriatic acid. Wear protective gloves and work in a well-ventilated area when using muriatic acid. Cleaning the concrete will not only prepare it for sealing but will also remove any white residue or efflorescence that appears on the surface of your countertop (Image 1).

Put the water/muriatic acid mixture in a bucket, thoroughly dampen a sponge and clean off the concrete with the sponge, removing any excess with a hand squeegee. Repeat this process until the white residue is completely removed.

To smooth the surface of the countertop, sand the surface starting with 120-grit sandpaper, then 180-grit, and finally 220-grit. Remove dust from the sanding with clean water.

Seal your countertop with a penetrating sealer. With gloves on, fold a clean white rag without any wrinkles. Fully saturate the rag with the sealer and run the rag along the surface of the concrete in long strokes (Image 2).

Overlap each stroke with the previous one. Allow the sealer to dry – it can take up to 2 hours -- and follow with a coat of sealer in the opposite direction.

Repeat this process, crosshatching coats, until the concrete does not absorb any additional sealer.

Apply a coat of beeswax to the concrete before installing it. The wax goes on with a clean soft cloth before being buffed off (Image 3).

Step 9: Install the Countertop

First, dry fit your countertop pieces to the cabinet tops (Image 1).

If the countertops are not perfectly level, add small wooden or plastic shims to create level surfaces. Once they are level, secure the countertops to the cabinet top (3/4” plywood) with cowpie-sized dollops of 100-percent silicone caulk placed every 4 to 6 inches. The concrete should be secured using a lot of caulk because it is still in the process of drying and could move or curl if not properly secured.

Once the countertops are set, caulk the seams using silicone latex caulk – (Image 2). You can use a colored caulk to match your countertop color. Tape either side of your seam with blue painter's tape, run a bead of caulk along the seam, run your finger along the seam, and when it is dry, remove the tape.

The countertop is done and in place. Maintain the countertop by cleaning it with mild detergent and water. Avoid products with ammonia.

Beeswax can be applied as often as needed.

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