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How to Complete the Form and Pour Concrete for a Vanity Top

DIY pros show how to complete building a form and pour concrete for a customized vanity top.

More in Bathroom

concrete vanity polished to smooth, matte finish
  • Time

    Day

  • Price Range

    $100 - $250

  • Difficulty

    Moderate to Hard

Highlights:

Step 1: Plan Knockouts for the Concrete Form

After making the basic form for the concrete vanity, create knockouts for the vanity faucet and drain hardware. The knockouts need to replicate the exact depth and diameter of the hardware, the specifications of which should be included in the packaging of the products. If the specifications aren't included, precisely measure the hardware.

In our project, we used PVC pipe filled with the foam used for the outside curve of the vanity (Image 1). (If the PVC pipe isn't wide enough to fit your knockout, expand the diameter with duct tape.)

As shown in the finished form, foam blocks created knockouts where the pipes for the sink faucets will run under the backsplash shelves (Image 2).

The hardware knockout needed for the drain pipe of the vessel sink brings up a common issue: the pipe for the sink is 1.5" long and the countertop is 2" thick. In our project, we attached a fist-sized 1" thick circular disk to PVC pipe to make a larger opening in the bottom of the countertop, allowing us to connect the hardware by hand.

Step 2: Finalize the Form with Knockouts

Using the completed vanity template as a guide, precisely transfer the location and measurements of the sink and hardware to the form. If you haven't finalized their location, map it out on graph paper (Image 1). Remember: once you set the knockouts, you won't be able to move them.

Secure the knockouts to the form with 100-percent silicone caulk. For the smaller pieces, add a screw so they don't move when the concrete is added (Image 2).

Finish the form by waterproofing with the caulk, applying a thin bead evenly around all the corners of the form (Image 3) and all around the knockouts. Follow by running your finger across the bead and push the caulk into the corner to create a watertight seal. Run your finger in one continuous sweep as stop and go marks will show up in the silicone and onto the concrete. Let the caulk dry.

Step 3: Cut Lath and Mesh

Use two kinds of steel - expanded lath and steel mesh - to strengthen the concrete vanity. Lay the template underneath each type of steel. Trace the template onto both types of steel with a permanent marker and mark your cutouts (Images 1 and 2).

Make the steel template slightly smaller, about a half-inch all the way around so it will fit easily into the form and won't show through the concrete. Cut the expanded lath with wire snips (Image 3) and the steel mesh with bolt cutters. Double check their measurements against the template before setting them aside.

Step 4: Prepare Glass Bits and Apply to Form

This project calls for adding colored glass to the vanity top as a design element. Purchase plate glass or colored glass from a hobby store or recycle glass bottles with labels removed. Place the glass you want to use into a five-gallon bucket.

With a sledgehammer and wearing safety glasses, break the glass into a variety of small sizes (Images 1 and 2).

Set the prepared form onto a level table near the location where you'll mix concrete. Cover all of the screw holes in the form with plumber's putty to make forming of the vanity easier. Next, add the colored glass to the base of the form (as the top of the vanity) spreading the glass evenly into the corners and mixing colors and sizes for variety.

Step 5: Mix the Concrete

Mixing the concrete is as precise as making the vanity form. To figure out how much material you'll need for the project, you need to first figure out the total weight of the countertop and then measure out parts by dividing.

A two-inch thick countertop weighs about 25 pounds per square foot. Calculate the total weight of your project by multiplying the vanity square footage by 25 pounds. Round up so you have a little extra concrete to work with.

For instance, a 4 foot by 3 foot vanity is 12 square feet with a weight of 300 pounds. Round up to 315 pounds so you have a little extra material to work with.

Divide the concrete mix into nine equal parts: three parts coarse sand (Image 1), three parts white playground sand (Image 2), two parts white Type II Portland cement (Image 3) and one part water.

All measurements are calculated by weight, so to figure the weight of each part, divide the project's total weight by the number of parts (nine parts total).

For example, each part of the 4 foot by 3 foot vanity (rounded up to 315 pounds) is 35 pounds. So you need to measure out 105 pounds (3 x 35 = 105) of coarse sand, 105 pounds of white playground sand, 90 pounds of Type II Portland cement and 35 pounds of water.

Note: Water weighs eight pounds per gallon, so in our project, we just a little over four one-gallon containers of water.

Measure out each ingredient ahead of time in clean five-gallon buckets, using the bathroom scale. To make the job easier, measure out the water in small containers to add a little water at a time.

Wearing a mask, add the dry ingredients to the wheelbarrow and mix them thoroughly with the perforated hoe. Then slowly add water, mixing until the cement texture turns from a crumbly mixture to an oatmeal consistency (Image 4)

Gauge your water amount carefully. To create a strong mix, the water amount should always be less than half the weight of the cement.

Step 6: Pour the Concrete

Add the mixed concrete in small batches to the leveled melamine form.

Add the first layer with your hands or a bowl so that the glass design stays secure at the bottom of the form. Fill up the form halfway (Image 1) and then remove air bubbles by banging the bottom and sides of the form with rubber mallets. Don't forget the corners. Continue to pound the form until no bubbles rise to the surface.

Next set the steel in the half-filled form. Set the expanded lath first and then the steel mesh on top of it. Make sure that none of the steel touches the edge of the form as this will show through in the finished vanity.

Fill up the rest of the form with concrete until it's flush with the form rails. Once full, pound the form with the rubber mallets until no bubbles rise to the surface. The concrete will settle a bit during this process so continue adding concrete and apply the mallet until it's flush with the edges of the form (Image 2).

Use the magnesium trowel to smooth the concrete (Image 3).

Lastly, cover the form with a plastic garbage bag (Image 4) being careful not to let the bag touch the surface. This cures the concrete via hydration, a chemical process by which concrete hardens. Let the concrete set up for about 48 hours before de-forming it.

In the final phase of the project, the form is removed from the concrete, the surface is polished and the vanity unit is installed

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