We're adding a shower to a half bath and during demo discovered drywall has been glued to the concrete block wall. Four feet of this wall will be used for tile in shower. Our Tiler says he can use Kerdi waterproofing but the inspector says we have to use furring strips over the drywall and 1/2 inch concrete board over that. Then tile. My question(s): 1) Do we need to install some kind of vapor barrier in this scenario? 2) Can we use insulation board between fur strips and if so, foil facing tile or away from tile? 3) Any other suggestion to do this per code?

Thanks! DParker

  • I would definitely ask this question over at the John Bridge Tile Forum. They have a lot of experts on the Kerdi sytem over there who are happy to help. johnbridge.com/vbulletin/forumdisplay.php?f=1 Commented Sep 15, 2016 at 18:18
  • 1
    Should be enough experience around here.
    – Chris
    Commented Sep 15, 2016 at 18:27
  • I'm unsure why your inspector said to use concrete backer on top of the furring strips. Was his suggestion to lay furring strips and in between rigid foam insulation?
    – Chris
    Commented Sep 15, 2016 at 18:35
  • I would remove the old drywall then put up furring strips to attach the backer to. Most block walls are not the best for a tile surface. I would want to eliminate any chance (that if the wall leaked or water penetrated the tile) for a mold haven that would really be tough to get rid of with the tile now there.
    – Ed Beal
    Commented Sep 15, 2016 at 18:46
  • Thanks Ed, and we did begin with that process but realized removing the drywall might take chunks of the cinderblock with it. It feels like cement, very solid. Commented Sep 15, 2016 at 18:51

2 Answers 2


There are not many options to resolve this properly. So I will address your questions first.

1) Do we need to install some kind of vapor barrier in this scenario?

The current best practice is to place waterproofing over the backer board and just under the tile. (ie Kerdi waterproofing)

2) Can we use insulation board between fur strips and if so, foil facing tile or away from tile?

The answer is no and for the same reason no vapor barrier is to be used behind the backer board. The wall cavity should be able to breath and allow any moisture to evaporate.

Updated: Based on finding out it is a basement

So my answer to you is: As mentioned by Ed - Spray with water to soften the drywall and it should easily come off to the paper.

Inspect and choose best method of removing glue: if it was glued unevenly. Maybe snap lines or draw lines as a layout for furring strips. (no need to do more work than needed)

Fasten furring strips, use backer board, seal (recommended) with (ie. Kerdi waterproofing) and tile over that.

  • I really think the glued Sheetrock should come out. The wall may be dry now but 1 good rainstorm could change than and the result could be a really nasty smell that is trapped behind the tile. If this room was above grade I would agree with you but not in a basement. no matter what glue was used it will only stick to the paper then the other 99% can be pealed off only leaving traces of paper on the adhesive. I just realized that the room location was not stated by the OP. if above grade +
    – Ed Beal
    Commented Sep 16, 2016 at 18:57
  • Oh that makes a huge difference. I was thinking it was ground level. Commented Sep 16, 2016 at 19:05
  • The room is on the main floor. The wall is an exterior wall. Thanks very much to everyone Commented Sep 16, 2016 at 19:52
  • I was thinking bacement. On a main level I would still remove the Sheerock. I think NorCal Johnny's answer is a good one so a + to him if you take this rout please give him an up vote it won't affect your score on the site but will give him credit for a good answer as I did.
    – Ed Beal
    Commented Sep 16, 2016 at 22:37

Very simple solution: just remove the drywall. It's easy; you can probably pull it down with your bare hands. Then waterproof the block underneath it and install tile.

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