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How to Prepare and Install Backer Board in the Bathroom

DIY host Paul Wilson walks you through prepping a bathroom for backer board installation.

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set tile around mirror

Step 1: Prep the Area

Tape a piece of plastic over the tub area, and for added protection put a piece of plywood over the tub (Image 1). This will protect the tub surface.

prepping the tub area

Step 2: Remove the Accessories

Remove the tub handles, trim and spout. Remove the existing tile using a hammer and pry bar (Image 1).

remove tub handles, trim and spout

Step 3: Measure the Area

Measure the area where the cement backer board will be placed. Pencil and chalk the area to represent the cuts that need to be made.

Step 4: Cut the Drywall

Cut out the drywall using a razor knife and drywall saw, and remove the old drywall (Image 1). Once all the drywall has been removed, check the studs to make sure they are plumb and on plane.

Step 5: Create a Vapor Barrier

Before you install the backer board, you need to create a vapor barrier that will help prevent moisture from going through the tile work, backer board and into the wall space between the studs (Image 1). You do this by using roofing felt.

Simply cut the roofing felt into strips to fit into the cut areas:

  • There needs to be a 6" overlap on vertical joints.
  • There needs to be a 2" overlap on horizontal joints, and also allow the felt to overlap the tub.

create a vapor barrier to prevent moisture

Step 6: Apply Sealant

Apply a silicone sealant between the felt and the tub lip to keep water from seeping through the joint.

Step 7: Secure the Backer Board

Pre-cut the cement backer board to fit the areas around the tub. Adhere the backer board according to the manufacturer's instructions using backer board screws (Image 1).

secure the backerboard

Step 8: Tape the Joints

Finish by taping the joints with an alkali-resistant tape and thinset mortar.

Warning: Don't forget to let the alkali-resistant tape and mortar set for 24 hours before you begin setting the tile.

Step 9: Add Tiles

Tip: When installing backer board, always start and stop vertical joints on a stud.

Lay out the trim tiles on top of the plumbing wall and on top of the tub skirt to find the best trim layout (Image 1). Measure the back wall, side walls, plumbing wall and tub skirt for their width and height.

Pencil in the level line in the area where the trim tile will meet the windowsill.
Lay out the field tiles and insert an accent tile on the floor to check where the measurements will fall on the new tiles.

The layout on the left and back wall of the tub for this particular project was easy. A bull nose tile was set on the left side of the top of the tub skirt to establish where the left-side wall tile would start. Then a level was used to make a mark where the trim tile would end and a line where the field tiles will start. The plumbing wall layout was established by the marks made earlier using the bull nose corner tile. It's this wall that dictated the layouts of the front of the plumbing wall and the tub skirt.

find best trim layout