Installing a shower in my basement, and am framing around a fiberglass 36 square shower base. should I put it flush against the frame and then attach cement board (it will overhang) or leave room to slide cement board between base and frame? Thanks!
I saw another answer that tells you to leave it above the flange of the base, but here is the problem with that and how I do it. If you leave it short of the base, there is now a gap however high the flange is with nothing to support the tile OR a place for the grout the sit because there is a void behind the tile. What I do is measure the thickness of the base ( usually 1/4) and then I rip a filler strip the same thickness as the flange. I nail it to the studs from the flange up to where you are going to stop the backer board or to the ceiling and then attach Hardibacker or Wonderboard to the furred out studs. Now the substrate can be installed 1/4 inch off the bottom of the base unit to avoid water wicking up and the tile has a full backing to within 1/4 of the base as well as the grout goes all the way in instead of sitting only BETWEEN the tiles as it would if you left it 1 1/2 up off the bottom sitting on the top of the flange. The only adjustment you will need to do is set the shower valve out whatever the thickness of the furring strips you add so it finishes on the tile surface to the manufacturers specs.
The framing goes tight to the shower pan, and the cement board goes down to the lip of the pan, but not over it. IMPORTANT: do not run the cement board over the lip or this will cause a bow at the bottom all the way around. Your tile will run down to the shower base. If you ran the cement board behind the shower pan the lip would stick out and when you tiled, the tile would be pushed out as described at the bottom row. I hope this makes sense to you.
