Sealing Between Backerboard & Drywall

Fiberglass Tape Approach

• 1

  Lay a section of adhesive fiberglass mesh tape over each seam where the backer board meets drywall.

• 2

  Apply a coat of thinset mortar — using a trowel — to embed each fiberglass tape.

• 3

  Smooth the thinset mortar until it is flat and free of ridges.

Drywall Finishing Approach

• 4

  Apply a layer of joint compound across the joint, using a 6-inch drywall knife. Lay paper tape along the joint, wiping it flat with the drywall knife. Immediately apply a thin coat of joint compound over the tape to hide it.

• 5

  Allow the joint compound to dry, which should take no more than 24 hours.

• 6

  Apply an additional coat of joint compound over the tape to hide it. Use a 12-inch drywall knife to apply a wide, smooth band of compound, hiding the tape completely. Let this coat dry and sand it smooth with 150-grit sandpaper.