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Construct a template out of thin door skin or laminate board. Hot glue the pieces together. Write any notes on the template (front, back, sink opening, etc.).
Lay 3/4” thick 4’ x 8’ laminate onto a large flat work surface. Turn template upside down on the laminate. Trace template with straight edge onto laminate. For the edges of the mold, cut strips of the 3/4” laminate to the desired thickness of your countertop. Our countertop is 1-1/2” thick. Secure the edge strips with a nail gun. Caulk edges with silicone. Let caulking cure for several hours. Once that dries, remove excess caulking with a razor blade.
Dampen a cloth with denature alcohol. Wipe down inside of mold with the cloth, cleaning off dust and debris.
Mix modifier and color in a concrete mixer. Add concrete to mixer. Add water to mixer and let it mix until desired consistency. Follow manufacturer’s instructions to achieve the best results. Note – The amount of material listed above is for a countertop measuring 5’ wide by 25-1/2” deep and 1-1/2” thick.
Transfer concrete into a wheelbarrow. Fill a small bucket with concrete and transfer it into the mold. Fill the mold about half way then vibrate it to remove air bubbles. The easiest way to this is to tap the bottom and sides of the mold with a rubber mallet.
Follow manufacturer’s recommendations for cure time. Depending on weather and temperature conditions, cure time may vary. Cover the mold with plastic to keep moisture in.
Grind the bottom of the countertop (the top of the mold that is facing up) until level and smooth. Use a diamond grinding wheel with dust collection system. If you don’t have a dust collection system, brush off dust and store in a cup. The dust mixed with some water can be used to fill in pinholes.
Using a diamond hand pad, lightly sand the bottom edges (the surface that is facing up) of the countertop. This reduces sharp edges and chipping during installation.
You’ll need at least two other people to help with this step. Slide the concrete mold to one edge to the table or work surface. Slide foam under one edge of the countertop. Lift the countertop vertically onto the foam. Lay out more foam for the rest of the countertop to rest on. Support the countertop as the mold top loosens.
Buff countertop. Sand rough edges. Wipe down the surface with a cloth dampened in denatured alcohol.
Use a cloth to apply food-safe sealer to countertop surface.
Wear gloves. Grab a handful of beeswax, rub all over countertop. Wipe gloves clean. Get a clean rag and buff off wax. Use an electric buffer for added shine. Test the application by pouring a small amount of water on the surface to see if the water beads off.
Get help with this step. Concrete countertops are very heavy and improper handling can damage or break the countertop. Make sure the area underneath countertop is supported by several wood crossbeams. Apply 100% silicone to surface that the countertop will sit on. Plastic shims can be used to level the surface. Check levelness of countertop. Let silicone dry.