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Community and Q&A

Waterproofing an already tiled shower

BPortnoy1 | Posted in General Questions on

Hello. Does anyone have suggestions for how I can possibly waterproof my shower without needing to take the tile off? Our contractors somehow left out the Kerdi system for our walls. There is a kerdi membrane installed on shower floor.  All my showers are membrane less (over cement) but this shower has wood studs not covered and the screws were not sealed either.  Looking for least toxic way to accomplish this. Thanks in advance!

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  1. Expert Member
    Akos | | #1

    This ship has sailed on that one without pulling it all out and starting from scratch.

    Good showers were built before Kerdi came along, so as long as the proper details were followed, the shower should work just fine with cement board.

    A quick go/no go on these is if the base can hold water. Pull the drain cover and plug it, fill the shower with about 4" of water. It should not leak out, if it does, the shower has issues.

    1. DC_Contrarian_ | | #4

      I agree that this is a fair test. It should maintain the water level for 24 hours.

      I'm still chuckling at "somehow forgot."

    2. BPortnoy1 | | #8

      Thanks will try

  2. monkeyman9 | | #2

    I dunno there is anything you can do now other than make sure the caulk is replaced right when it's cracks and peels. The grout is all in?

    1. DC_Contrarian_ | | #3

      Tile is not waterproof. Even if you maintain the caulk you can't count on it to keep water out. The waterproofing has to be behind the tile.

      1. monkeyman9 | | #5

        Right but that's all he can do except rip it down.

    2. BPortnoy1 | | #19


  3. Expert Member
    Michael Maines | | #6

    The Tile Council of America handbook (2016 edition) says that "A waterproof membrane or vapor retarder member must be specified to prevent moisture intrusion and protect adjacent building materials."

    Is the tile natural stone or ceramic/porcelain? You might be able to get by with a surface-applied sealant but it's definitely risky. The right thing to do is to tear it all out and start over.

    1. BPortnoy1 | | #7

      Thank you. It was def specified and paid for but contractor is out of picture.

      It's marble. Any suggestions for sealant to use? Thanks!

      1. BPortnoy1 | | #9

        I will eventually rip it out but may not be able to for a year or so

        1. Expert Member
          Michael Maines | | #10

          No, I used to do a fair amount of tiling but I haven't kept up with the latest products. I would go to a custom tile supplier and ask what they recommend. Probably something like this:

          or this

          This is a good forum for tile-related questions:

          1. BPortnoy1 | | #11

            Thanks so much

      2. DC_Contrarian_ | | #20

        In my experience marble can be problematic in a shower, it's a fairly porous stone and discolors when it gets water in it. Even if you seal the visible portion water still gets in. Note that this is a problem with marble even in a properly waterproofed shower, the waterproofing is to protect the house behind the tile and not to keep water away from the tile.

        My inclination would be to do the stopper test, and unless it fails egregiously just to live with it. If it leaks a little it's not going to create enormous damage, when it's time to replace the shower it won't add much to replace a few rotted 2x4's too. You never know what life throws at you, you may end up replacing that tile because your life changes sooner than you think.

        1. BPortnoy1 | | #21

          Makes sense. Thank you!

  4. walta100 | | #12

    Did the contractor explain to you how your walls and shower floor was water proofed?

    There is more than one way to build a waterproof shower but they are all unforgiving in that the tiniest of mistakes means a water leak that becomes mold and rot given some time.

    If all they did was nail cement board to the studs and slap on the tile my guess, is it will all get redone in less than 5 years.

    From the photos it looks like the floor may be curb less making it very difficult/ impossible to test the floor pan.


    1. BPortnoy1 | | #13

      Hi. We do have a curb thankfully. We had discussed the schluter system and paid for it so that was the go to plan. However I looked back at photos and can see that they only did the corners. The contractors and tile guy are now not responding so hard to get more info. Really trying to avoid mold and rot. I wonder if I can at least save the tile if I redo it.

      1. Expert Member
        Deleted | | #14


        1. BPortnoy1 | | #15

          Oh yes. The first shower is marble. I'm most concerned about one with the exposed wood. But concerned about all of course. The others are ceramic and porcelain. Seems like I need to rip them all out. I'll check out that forum for best way to waterproof. Thanks Michael!

          1. Expert Member
            Michael Maines | | #18

            I deleted my reply after re-reading your initial post and seeing that you have multiple showers. For anyone wondering what I had written... I'm sorry you're in this situation; facing demolition of what looks like perfectly good work must be difficult.

  5. walta100 | | #16

    I would test the floor pan as shown in this YouTube video.

    If it can hold a few inches of water for 24 hours I would decide that the walls are going to be water tight unless there is evidence of an active leak below the shower. I seem to recall that marble would change color when its backing board is wet.

    Removing and reinstalling tile is almost never worth the time required to make it happen.


    1. BPortnoy1 | | #17

      Thanks so much

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