As in title.

I want to glue and screw the backer board into the walls down to the slab before pouring the shower pan in a redguard shower, as I have about 1/2" spare space between the wall I'm adding and the water heater.

I don't want to be messing around with levels and shims and such; the floor is level enough, the walls are 90 to the floor, if the whole thing is cocked 5 degrees I don't care as long as it's all the same 5 degrees .

Thing is, I can't find any (halfway) reliable info on what cement board can be embedded in a shower pan and what can't.

You'd think that you could embed anything shelf stable in concrete if it was getting a membrane applied on top but maybe not?

Please, put me out of my misery.

  • 1
    Do you want this to go under the concrete? Do you already have the pan on the ground made of poured concrete? I'm very confused by what, exactly, you're looking to do. Maybe make a quick sketch showing us how you're going to layer things - doesn't have to be pretty or to scale, just ID what goes where.
    – FreeMan
    Nov 1, 2023 at 23:54
  • go with a fleece backed membrane. red guard alone is a guaranteed leak. any settlement and it will crack. the fleece membranes at least would need excessive force to rip and leak. You are putting a water heater in your shower? concrete or deck mud? Nov 2, 2023 at 0:37
  • Typically the backer board stops short of the preslope so that the pan liner can go behind the backer board. In this configuration the pan liner doesn't get punctured by backer board screws because instead of fastening the backer board down low, you instead use the pressure of the shower pan to push the backer board against the wall.
    – popham
    Nov 2, 2023 at 1:25
  • 1
    Do you intend to RedGard the floor, too? Maybe use fiber reinforcement tape around the bottom edges?
    – popham
    Nov 2, 2023 at 1:36
  • Yes, I'm taping all the seams and corners and redguarding the floor, then tiling on thinset directly ontop of the redguard. I've actually used redguard before, but never as waterproofing; only as crack prevention for iffy tile installs. Also this shower is on a slab with two exterior walls and one interior wall that is very visible; it's why Im willing to try somthing new. Nov 2, 2023 at 5:45

1 Answer 1


I have no specific info from the manufacturers, however I have done just as you describe many times with Durock.

I've been doing showers that way for over a decade, probably close to 2. I never have had any incident of failure.

  • What's your attitude on rough side versus smooth side facing inward? With a RedGard membrane, I decided that smooth side was just fine and takes less waterproofing, but I've never felt confident that it was The Right Way.
    – popham
    Nov 2, 2023 at 1:42
  • 1
    I find most of the newer sheets are marked rough side for thin set, smooth side for mastic. Thin set is always used in a shower, so it's rough side out. I always apply 2 coats of RedGard or AquaDefense. It is pricy, but in the long run it's your best defense.
    – RMDman
    Nov 2, 2023 at 5:45
  • I reasoned that the rough side was for the thinset to key into, where the waterproof membrane would nullify any bonding benefits from the roughness. First time I used a membrane, though, I didn't know to prime, the surface was all splintered, and I had to spend a fortune on extra waterproofing to assure myself that I had a good coating. Maybe the smooth side thing was just my face-saving cope for screwing it up.
    – popham
    Nov 2, 2023 at 5:55
  • I always use a modified thinset. The polymers make the tiles stick like peanut butter on bread.
    – RMDman
    Nov 2, 2023 at 5:58
  • Just to confirm: some type of water proof sheetrock product to the slab, mud pan infront of sheetrock, tape seams, tape angles, then 2 coats of my membrane of choice right to the ceiling, correct? Nov 2, 2023 at 15:53

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