Installing Concrete Backerboard

Concrete backerboard is usually used as an underlayment for ceramic tile. It can be used on walls, floors or countertops.

Concrete backerboard has a solid concrete core and is faced on both sides with fiberglass. It's an ideal underlayment for wet areas like shower walls and bathtub surrounds.

Some backer board is a bit thinner than drywall. If your backer board meets a drywall surface, you may have to first fur out the studs with strips of builders felt to make the surfaces flush.

Cutting Concrete Backerboard

Cutting backerboard is a lot like cutting drywall, except that backerboard is much harder. Using a framing square, score your cut line a few times. You can use a regular utility knife for this, but you'll go through a lot of blades. A special carbide-blade cutter works better.

TIP: If you're using a utility knife, shorten the blade to keep it from breaking.

Break the board by applying pressure until it snaps apart along the score line. You'll probably have to cut through the fiberglass on the back also.

Installing Concrete Backerboard

Start installing backerboard at the furthest back wall and work your way from the bottom up.

TIP: If you're working in a bathtub or shower put a blanket down before you work to protect the surfaces from getting scratched or chipped.

Use galvanized nails or screws to secure the backerboard. If you're working above a shower pan, be sure to nail or screw above it so you don't puncture the fabric.

The ends of the backerboard sheets should be centered over the studs, but stagger the joints so they don't line up with one another. Leave about 1/8" space between the sheets of backerboard.

Cut holes in the backerboard for around shower and bath controls. Score the mesh on both sides of the board and hammer on it until it breaks out.

Finishing Concrete Backerboard Seams

You want to mud and tape the joints of the backerboard also.

First fill the joint with tile adhesive using a taping knife, Then put fiberglass tape over the seam and put more tile adhesive over that.

Like drywall, the sheets have tapered edges, this allows you to fill the joints and still stay level with the backerboard. For a ceramic tile underlayment, one coat of mud is enough.