Installing backer board has become a very popular choice for a wall substrate in the shower. Backer board bridges the gap between effectiveness and expense, giving you many years of durable construction given that it is installed properly. The advantage of this material is that, while not waterproof, it is dimensionally stable in wet conditions and does not swell up. Here are the steps to install tile backer board in your shower:
Waterproofing the Studs
When installing the backer board, you need to have a vapor barrier between the board and the studs on the wooden wall. While the board does not swell with water, the studs will, so you should prevent moisture from reaching them. A suitable material for a vapor barrier is a 4mm or thicker plastic sheeting that you can purchase at a home depot or hardware store. It is more preferred over tar or roofing paper.
To waterproof the studs, take the plastic sheeting and staple it (though you can also use silicone) to the studs in a way that it completely covers the entire surface inside your shower, making sure that it overlaps all the edges. Like what you would do when hanging wallpaper. Also, make sure that it sufficiently covers the frames, so if you were to spray the walls with water, the framing and the studs will not get wet. The same goes for the bottom of the barrier, where you should make sure that the barrier overlaps the shower side of the shower base or tub to ensure water running down the plastic sheeting will roll off into the tub, instead of behind the tub.
Installing the Backer Board
1. Secure the things that you will need, including plastic sheeting, staple gun with staples, silicone caulking, utility knife with replacement blades, drill, handheld keyhole saw, putty knife, 1.5-inch wood screws, work gloves, safety glasses, dust mask, T-square, tape measure, drywall mesh tape, rot and pencil.
2. Before installing the tile backer board, decide the best way to do it, where your priority is the ease of installation whether it is vertical or horizontal placement. If you have a shower room that is wide enough, then it is best to place the sheets on their longest edge, and if not, you can run them with their length going up and down.
3. Cover the studs on the wall in plastic sheeting that are cut down to size with your utility knife to function as moisture barrier for the studs behind the board. Layer and staple the sheets into place using a waterfall method, so each upper piece will drain down onto the next lower one all the way down to the shower pan. Make sure that the sheets’ lowest edge covers the pan flange.
4. Split any board pieces that need to share a stud across the stud’s width, ensuring that each piece mounts to the stud and share the piece. If a piece of board extends beyond a stud, you need to cut it down to the last stud that it crosses and then cut down another board piece to a size that enables it to properly share the opposite side of the stud.
5. Measure and mark the backer board pieces and then make straight cuts using your utility knife. Holding the T-square against the plastic sheet, guide your utility blade down the length of the cut and then break it along the scored surface line. To free up the cut-off, fold the piece and then cut its back side with the knife.
6. Using a keyhole saw, make some cuts around pipe stub-outs, such as faucets and shower heads, and the same goes for drywall. You can do this by pushing the tip of the saw into the board and then saw your way around the cut-outs.
7. Stack the board pieces up your wall, starting with the lowest piece first to tap the power of gravity. As most likely you will be working on this alone, you can place 2 screws slightly into the wall above the shower pan, so you will be able to rest the first sheet on top of the screws while screwing the sheet in place. As for the following pieces, they can just rest on the top edge of the first and lower piece.
8. Mount each backer board piece to the studs and then drill through the board into the studs. Place some screws in about every 6 inches up the studs and within about .5 inch from any edges, leaving at least a .125-inch gap between all pieces to allow movement for expansion.
9. Using silicone caulk, treat the gaps between pieces and the gap from the lowest piece on the shower pan. Smear silicone over the screw heads using a putty knife.
10. Place drywall mesh tape over the edges of any pieces that connect on an individual wall, but don’t tape the inside corners. Apply it just like masking tape and it will stick to the drywall until you apply thin-set for the tile installation.
Allowing and Disallowing Movement
You would not want the backer boards butting against one another, so you should leave a small gap at every change of plane, such as corners between the walls and ceilings, floor and tub. Basically, there should be room for contraction and expansion caused by wood. To ensure this will be effective, check if the movement will not interfere with your tiles. If you have a shower base or tub, it is recommended to stop the backer board about .125 inch above the lip. As you can see, you should not run the board over the lip’s edge as it will cause the board to bow out, which means that your wall will not be flat.
Disallowing movement should be done if your shower framing does not allow you to place the edges of all the boards directly over a stud, which means that you must add more studs. Also, make sure that every edge of the board is supported, so the spot would not move if the wall is leaned on or pushed.
To complete the job, you should mud and tape your seams in a similar way you would to a regular drywall, where all in-plane joints need to be taped. Make sure that the tape is alkali-resistant, as your thin-set would contain alkali that will eventually erode regular tape.