A concrete backerboard is required for all tile or natural stone showers. It serves as a shower wall substrate that will help protect the wood of the wall studs from moisture. It is not waterproof but it is installed with a moisture barrier. A benefit of using cement backerboards is they remain dimensionally stable even when wet so they do not swell up, which will lessen the occurrence of tile cracking and other bathroom problems.
You have to make sure your concrete backerboard is properly installed to have a solid and durable substrate for your tile installation. Take your time when installing the sheets and ensure that you make it as moisture-resistant as possible.
1. Decide if you will go with vertical or horizontal placement when installing your backerboard in the shower. It really won’t affect the outcome, but it is important to make the process easier. For wide shower areas, it is better to place the boards on their longest edge. But if it will make the installation more difficult, then run the sheets vertically instead.
2. Cover the wall studs in plastic sheeting. This will serve as a moisture barrier for the wall studs behind the backerboard. Use a utility knife to cut the plastic sheeting down to size, staple the sheeting into place, then layer them using a waterfall method (each upper piece drains down onto the next lower sheet, directing the water down towards the shower pan). Make sure that the shower pan flange is covered by the lowest edge of the sheeting.
3. Lay out your boards for the best fit on the walls. Measure and mark your pieces, then make straight cuts using a utility knife and T-square that is held against the sheets.
4. Use a keyhole saw to cut around for pipe stub-outs (such as faucets and shower heads).
5. Starting with the lowest piece, start stacking your boards up the wall. Place a couple of screws slightly into the wall about 1/8 inch above the shower pan. This way, you can rest the first piece on the screws while you are screwing it in place. When the most bottom sheet is screwed in place, you can rest the next board on top of the lower sheet.
6. Mount the boards to the wall studs by drilling the board into the studs. Make sure to place screws every 6 inches or so up the wall studs, within ½ inch from edges. Remember to leave a gap of at least 1/8 inch between sheets to allow movement during expansion and contraction.
7. Fill the gap between boards with silicone caulk. Do this also with the space between the lowest piece and the top of the shower pan.
8. Smear silicone over the heads of the screws using a putty knife.
9. Tape the seams by placing drywall mesh tape over the edges of sheets that connect on an individual wall except the inside corners.
10. Before proceeding to tile installation, fill all the gaps in the seams with thinset.
