Dear James: I saw decorative concrete countertops at a home show, and I want to try it myself. What is the basic procedure for making my own concrete countertops for my bathroom and kitchen? —Farida T.
Dear Farida: These types of decorative and colored concrete countertops are becoming very popular. They are attractive, low-maintenance, and reasonably priced. Each concrete countertop is made in custom mold, so you can create any unique shapes and colors you desire.
Use your bathroom countertops as training for the kitchen one. Although this is not a difficult project, there is a learning curve, and it makes sense to start on a small countertop. Working with concrete takes some practice. Just small variations in the amount of water used can make a big difference in spreading the concrete and the finished surface.
The first step is to design the shape of the new vanity top. Try to keep it as simple as possible since this will be your first attempt at making a concrete countertop. Plan on forming the bowl with concrete so it is integrated with the vanity top. This looks nice and eliminates the possibility of leaks and dirty joints and seals.
You will need a strong table at least the size of the vanity top. Even a small vanity top can be quite heavy when it's made from thick concrete. Braces for the sides of the form can be screwed into the wooden top, so the tabletop will be ruined unless you first place a piece of plywood over it.
The basic form for the vanity top is made from 3/4-inch melamine. This material is relatively easy to cut to size and to work with. Its surface is smooth, so the top and sides of the concrete vanity will also be smooth when the form is removed. Support the outside of the melamine side pieces with 2-by-4-inch lumber, and then screw braces into the tabletop.
Making the form for the sink recess is a bit trickier. Build a simple rectangular tapered design, with the deepest area near the back underneath the faucet. Glue a piece of polyvinyl chloride, or PVC, pipe to the sink recess form to create a hole for the drain pipe when the concrete is poured. Additional small side forms will be needed around the recess to create the proper concrete thickness.
The final preparation step is to make a rebar, short for reinforcing steel bar, cage to be embedded in the concrete. Concrete is very strong in compression, but it needs steel reinforcement when spanning a vanity. Use steel wire to connect the rebar pieces together into a cage.
Mix and color the concrete to be poured into the vanity top form. A typical mixing ratio is 3 parts of white sand, 1 1/2 parts of 3/8-inch gravel, and 1 1/4 parts of Type 1 Portland cement. Adding a water reducer and plasticizer can make the wet concrete flow better. Use a vibrator to make the concrete flow into all the corners.
When the concrete is set, remove the forms. Lightly grind the surface with an abrasive pad to expose tiny bubbles. Fill them with a thin coat of colored concrete and acrylic bonder. Apply sealer and a coat of wax.