How to Pour a Concrete Vanity Top

1. Measure the Cabinet and the Sink

   With the tape measure, measure the width and depth of the sink cabinet from the top (with no countertop). If you intend to install a new sink, a paper or cardboard cut-out may be included to help you mark out the dimensions of the sink. If the faucet and controls come up through holes on the sink, you will not need to add holes to the concrete vanity top.

2. Build the Vanity Top Template

   Countertop templates are pieced together from thin strips of wood or cardboard. This helps the countertop conform to any wall or cabinet variations.

   On the base cabinet, lay out strips of cardboard or 1/8-inch thickness wood project panel and glue them together with the glue gun to create a template for the perimeter of the vanity top.

   Tip

   Remember to account for countertop overhang. Counters typically overhang 1 1/2 inches to 2 inches on the front and sides. There is no overhang in the back because the countertop will be flush against the wall.

3. Draw the Vanity Top Shape on the Form

   Lay the vanity top template on top of a melamine-faced medium-density fiberboard (MDF) panel, common thickness 3/4-inch. If the back side of the template is straight, then place it against one of the factory-cut sides of the board. Make sure there is space around the other three sides of the template. Clamp down the template. With the marker, draw the vanity top shape on the board. Also draw the sink cut-out.

   Tip

   The melamine-faced side of the board must be pointing up.

4. Cut the Bottom of the Form

   Use the circular saw to cut the concrete form along the lines that you drew on the board. To cut perfectly straight lines, you may want to use a saw guide. Do not cut out the sink cut-out.

5. Cut and Build the Sidewalls

   Strips of melamine board that rise 2 inches from the bottom of the form will act as sidewalls to create a container for the wet concrete. With the bottom of the form on a table and the melamine side facing up, lay the sidewall material against the sides of the form. The edges of sidewall material must rest on the table.

   Measure up 2 inches from the bottom of the form and mark the cut point with the marker. Use the circular saw to rip four sidewalls, one wall for each side of the form.

   Screw the sidewalls to the sides of the concrete form bottom with the screws. Check for square with the Speed Square and adjust as needed.

   Tip

   Only use screws when attaching the sidewalls. Do not glue or caulk them into place, because they later must be removed.

6. Cut and Build Sink Sidewalls

   Cut strips of melamine board 2 inches wide. Piece these together and cut as necessary to form the shape of the sink cut-out. Attach to the form bottom from below with screws. Keep this cut-out square with the Speed Square.

7. Bevel the Edges

   By adding silicone caulk to all of the 90-degree joints and then rounding the caulk, you create the reverse appearance after the counter is released from the form. The reverse is a rounded, or eased, edge. Caulk also prevents the concrete mix from seeping through the seams between the sidewalls and the form bottom.

   Put on a pair of latex gloves. Squirt silicone caulk into all of the 90-degree inner joints on the form. Then, use a marble, the end of a glue stick, a ball bearing, or any round or circular item, and draw the item through the caulk. Wetting the item with water will help it move through the caulk without sticking.

   Do not overwork the bevel. Aim to draw through the caulk just one time, if possible. Two parallel rows of caulk will form on the sides of the bevel bead. Do not wipe these off since you will be able to remove them later.

8. Clean the Excess Silicone

   Let the silicone dry for at least two hours. Once the silicone is fully cured, peel off any excess with your fingers. You can also use the straight razor or a loose utility knife blade to carefully remove the silicone.

9. Cut the Rebar Mesh

   Use the hacksaw to cut the rebar mesh to 1 inch less than the size of the vanity top. Be sure to cut out the center area for the sink.

10. Add Oil to the Form

    Melamine is used for the inside of the form because concrete does not stick well to it. Even so, it helps to add mineral oil to the inside of the form to help the form and the cured concrete to release from each other. Apply the oil liberally with cotton rags but do not allow the oil to pool up.

11. Mix and Pour the Concrete

    Put on latex gloves and breathing protection. Cut open the bag of concrete and pour it into the mixing tub. Mix in the amount of water as recommended by the manufacturer. With the hoe, mix the concrete and water.

    Pour the concrete into the form. Avoid the center sink cut-out; this does not receive concrete. Push the concrete around the form by hand, making sure that it reaches all edges and corners. Use the paint roller to push the concrete around and downward. Pour the concrete up only halfway for now.

    Tip

    At this stage, work with a partner. The partner can mix the concrete and pour it into the form, while you work the concrete by hand.

12. Add the Rebar Mesh

    With the concrete halfway in the form, add the rebar mesh. Push it down firmly into the concrete. Use the paint roller to press it down even further.

    Tip

    Make sure that the rebar cut-out area lines up with the intended sink cut-out section.

13. Vibrate the Form

    Vibrating the concrete form eliminates holes and other voids, especially those that develop on the bottom of the form and on the edges. Tapping the form with a rubber mallet helps to settle the concrete. If you have any type of vibrating tool such as a sander or a hammer drill, you can use these, too.

14. Screed the Concrete

    Have one person continue to add mixed concrete on top of the rebar, as the other person vibrates the form. Once the concrete reaches the top of the form, use a scrap piece of two-by-four to screed off the top of the concrete.

    What Is Screeding?

    Screed means to level off the top of wet concrete by moving a board back and forth while pulling it toward you. This is only a rough, initial leveling; smoother leveling comes later.

15. Trowel the Concrete

    Immediately after screeding, use the masonry trowel to smooth down the concrete. A smooth top (later to become the bottom) will help the vanity top seat better on the vanity cabinet.

16. Cure the Concrete

    Lightly mist the concrete with water from the spray bottle, then cover it with sheet plastic. Keep it out of the sun to slow the curing process. Concrete that dries quickly is more likely to crack and break. Let the concrete cure for at least three days. Keep the concrete lightly damp during this process.

17. Remove the Form

    Use the drill to remove the screws that hold the form together. If you can, pull the sidewalls off of the vanity top by hand. If you cannot, lightly tap it off with a rubber mallet. With a helper, turn the concrete vanity top over with the bottom of the form still attached. Pry the form off of the top of the vanity top.

18. Sand the Edges

    The silicone bevels go a long way toward smoothing down the vanity top's edges. But some sharp lines will still remain. Use an orbital sander with 220 grit sandpaper to take off these lines.

19. Sand the Vanity Top

    Sand the top of the concrete vanity top with the orbital sander. Work up to a sandpaper grit of #320. If, along the way, you encounter voids, fill them in with a mixture of Portland cement and acrylic fortifier.

20. Seal the Vanity Top

    After thoroughly cleaning the vanity top, apply a minimum of four coats of sealer. Each coat should dry completely before you move to the next coat. Finish with countertop beeswax or equivalent.

Tips for Making a Concrete Vanity Top

• Always work with a partner, not just for lifting assistance but to keep the concrete from hardening on you.
• For better access when building the form, work on a table, not on the ground.
• When you pour the concrete, the form must be on a perfectly flat and level surface. Check with a bubble level.
• Set a timer to remind yourself to regularly mist the concrete after the pour.