How to Replace a Backer Board in the Shower

Cut through the sealant surrounding each piece of the old backer board with a utility knife.

Remove the screws or nails holding the top piece of backer board on the shower wall, using an electric drill to loosen the screws or a hammer to pull the nails. Discard the loose piece of backer board. Repeat this for each piece of backer board in the shower stall.

Clean the old backer board's debris from the shower stall with a broom and dustpan.

Inspect the shower wall studs for damage. Repair or replace any damaged wall studs as needed.

Measure the shower's longest wall with a tape measure. Transfer the measurement to a new backer board, placing a pencil mark at the appropriate spot on the backer board's printed side. Lay out the cut on the backer board's printed side with a pencil, using the measurement mark as a placement guide and a framing square as a straightedge.

Score the backer board along the pencil layout line. Stand the backer board on its edge and fold the backer board across the scored line. The backer board will snap in two along the scored line.

Place a shim on the shower floor next to each shower wall corner.

Set the cut piece of backer board against its respective shower wall, using the shims to hold the backer board off the shower floor. Secure the backer board to the shower wall studs with either 1-inch drywall nails or 1-inch drywall screws. Use the hammer to drive a drywall nail, or the electric drill to run a drywall screw, every 8 inches along each wall stud.

Measure, cut and install each addition piece of backer board in the shower, using the same method used on the first piece.

Remove the shims.

Fill each backer board seam with Type 1 wall mastic, a type of mastic designed specifically for wet areas, using a margin trowel to force the mastic into the seam's recesses. Pay special attention to the seam around the shower floor and the corner joints.

Apply a strip of mastic mesh to each backer board seam, using the utility knife to cut the mesh to size. Center the mesh on the seam and press the mesh into the mastic with a plastic squeegee. Remove any excess mastic with the squeegee. Let the mastic dry completely before installing tile.