How to Cast a Concrete Vanity Top

Measure the length and width of the vanity’s base cabinet. Add up to 2 inches to the width for the front overhang. If desired, add an additional 2 inches to the length for overhangs on the side.

Determine the size, shape and placement of the opening for the sink. Most sinks have a template pattern and placement information that you can use for the outline of the sink’s opening included with their assembly directions.

Trace the template for the sink’s opening onto a piece of 2-inch-thick scrap lumber. Cut out the pattern, using a circular saw.

Cut melamine pieces to the dimensions you determined in step 1 using a circular saw to create a form for the concrete countertop. Melamine has a nonstick surface that allows you to remove poured concrete easily from it. Cut 2-inch-thick strips for the sides of the concrete vanity top form.

Assemble the melamine pieces on a level work surface with the nonstick surface on the inside of the form. Use screws to hold the form together. Clean the inside of the form with a shop vacuum when you finish.

Set the piece of scrap lumber that you cut into the sink’s outline inside the form where you plan to install the sink. Run a bead of silicone caulking around the lower edge of the wood to hold the board in place inside the form.

Spray some spray adhesive into the bottom of the form. Arrange decorative pebbles or other objects that you want to display on the top of the concrete vanity top in the bottom of the form. Omit this step if you are not using decorative inlay items.

Measure and cut galvanized wire mesh to slightly smaller dimensions than for the countertop. This will serve as the reinforcement bar, or rebar, to keep the concrete countertop from cracking. Cut out an opening for the sink using wire cutters, as well. Set this aside for now.

Mix concrete countertop mix and color pigment together. Add fiber reinforcement included with the countertop mix to make the cured concrete stronger. Add water following the directions on the countertop mix package. Stir the concrete mixture well.

Place enough concrete into the form to cover the decorative items in the bottom of the form. Work the concrete into the corners. Set the cut mesh rebar over the concrete. Finish filling the form. Tap the outside of the form with a rubber mallet to help settle the concrete and work out any air bubbles in it. Use a trowel to smooth the surface of the concrete. Allow the vanity top four days to dry.

Remove the screws holding the form together. Pull away the melamine sides. Move the vanity top, with the help of an assistant, off the bottom of the form. Pop out the piece of wood used as the sink marker and remove any caulking that remains on the concrete. Turn the countertop so it is face up.

Dampen the surface of the concrete. Smooth the surface of the concrete with successively finer sandpaper in an angle grinder. Start with 50-grit sandpaper. Switch to 100-grit and then 200-grit sandpaper. Finish the top with 400-grit sandpaper. Keep the surface damp as you change sandpapers. Smooth the sides as well. Use 800- and 1,500-grit after the 400-grit sandpaper on the sides to make them even smoother so they won’t snag your clothing.

Apply a concrete sealer to the concrete vanity top following manufacturer’s directions. Once the sealer dries, the countertop and its sink are ready to be installed on the vanity cabinet.