Cement Board and Aqua Defense Waterproofing for a Shower Wall

Cement board for a tiled shower comes in half-inch and quarter-inch sheets, typically 3 ft by 5 ft, and the installer in this walkthrough puts half-inch on the walls and quarter-inch on the floor, where the subfloor already acts as a backer. Brands named are Hardy Backer, Permabase (the product used here) and Durock. Tile should not go over sheet rock in a tile shower, which he says will break down over time.

Protect the pan and start at the back

Before any board goes up, the shower pan is covered with cardboard and a piece of scrap sheathing cut to the pan's size, so dropped items do not crack it. The tub and shower here is the standard 5 ft long, which matches the 5 ft sheets. Starting on the back wall means the first sheets need no cutting; installing the side walls first would shrink the back and force trimming each piece.

Hanging the board

Supplies are wall board adhesive (a 28 oz tube of Heavy Duty Liquid Nails), 1 5/8 in. cement board screws, an impact driver or drill, and a caulk gun. Working alone, he measures to the first stud, marks the 16 in. on-center layout on the sheet, and starts a screw at each stud center before applying adhesive, so the board can be tacked up quickly. Adhesive runs down each stud only as far as the sheet being placed, so it does not set up early. After tacking, a screw goes in about every five or six inches across the studs: roughly 30 screws per half-inch wall sheet and about 60 per floor sheet. Screws should sit just below the surface.

Cutting

The bottom piece is ripped to about 33 inches using a chalk line. Options are a diamond blade on a circular saw, a scoring knife (which throws a lot of cement), or an oscillating tool, which he found best for limiting dust and crumbs. Ear protection is advised, and scrap plywood goes under the cut so the subfloor is not cut. A small strip is notched from the back so the board clears the lip of the shower base and does not kick out at the bottom. The shower head hole is located by measuring 17 inches up and 15 and a half over, then drilled with a 1 1/4 in. bit.

Tape and thinset

Fiber mesh tape is tucked into the corners and laid over the flat joints, which have a slight indentation for mortar. Thinset made for porcelain is mixed with a drill and mixing blade to a peanut butter consistency over one to two minutes, left five to ten minutes, then remixed. It is packed over the tape with a drywall knife, over every screw, and around the shower valve so the waterproofing seals there. It then dries overnight.

Waterproofing

Aqua Defense is stirred thoroughly, since it is thick and almost like jello, and rolled on like latex paint with a brush for corners; goggles are worn. The shower base is masked first. The first coat soaks into the board, and the second takes less product. He waits about 30 to 40 minutes between coats, and two coats used about half a bucket. Masking tape comes off while the coating is fresh so it does not pull the waterproofing off as it dries.