Q. My vanity countertop and sink need to be replaced. I thought about making a custom-colored concrete one myself. If it goes well, I will try it for the kitchen. What are the basic steps for this project?
Concrete is a reasonably priced, readily available, environmentally friendly material. Since it is formed in a mold, custom shapes and styles are possible.
Making a concrete countertop is not a difficult project, but it will take a little practice and a lot of initial research to do it properly. The basic construction concept is fairly simple, but mixing and working with the wet concrete is often more of an art than a science.
Create the forms: The first step is to design the shape of the new vanity top. Keep it as simple as possible.
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 table top 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 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 PVC pipe to the sink recess form to create a hole for the drainpipe when the concrete is poured. Additional small side forms will be needed around the recess to create the proper concrete thickness.
Make rebar cage: The final preparation step is to make a rebar (reinforcing steel rod) 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 piece together into a cage.
Mix the concrete: Mix and color the concrete that will be poured into the vanity top form. A typical mixing ratio is three parts white sand, 1 1/2 parts 3/8-inch gravel and 1 1/4 parts 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.
Remove the forms: 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.
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