Why does drywall work in a Kerdi Shower?

Discussion in 'Shower & Bathtub Forum & Blog' started by jadnashua, Jan 26, 2014.

  1. loudgonzo

    loudgonzo New Member

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    Debonding of membrane to substrate is a different issue not discussed in this thread. I'm actually waiting for input on this very topic at this thread

    http://www.terrylove.com/forums/showthread.php?54202-Inspection-Check-List-for-Kerdi-Shower-Builds&p=407181&viewfull=1#post407181

    A faulty valve or a bad connection is just that, but the point I'm asking is that using cbu can mitigate OTHER problems that drywall can't.
  2. eurob

    eurob master tile and stone installer

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    615
    Location:
    Montreal
    Drywall will be dammaged beyond the point of safety for the assembly.

    CBU will keep the integrity even if fully soaked, which probably will not happen without visible signs or leaks.
  3. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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  4. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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  5. dhagin

    dhagin builder:anti-builder

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    Don't get me wrong fellas, I think backer board under Kerdi is a fine idea - AND, backer board is an approved substrate by the manufacturer, as are many other options. Don't tell anyone, but I've done it myself. Backers like Permabase/Dalbase install similar to drywall and don't cost that much more if you're inclined to go that route. I got no problem with that. :)

    Carry on. :)
  6. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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  7. jim mills

    jim mills New Member

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    Location:
    nebraska
    All good answers as to why use CMU as opposed to drywall. Interesting that it is so promoted by Schluter & JB forum. I see my local Home Depot now carries
    Schluter products. I see that as a negative towards the company & their products. The DIY'ers will ruin their reputation IMO. Interesting fact that in Europe, modified Mortars are used to seam Kerdi.
  8. DonL

    DonL Jack of all trades Master of one

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    You guys Crack me up.

    This is the kind of backing to have in the shower.

    Crack_.jpg


    Better when Wet.
  9. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    If you test your plumbing before you close up the walls, and it is done in a workmanship like manner, what percentage of times does it leak? Practically zero. Why is it such a stretch to understand that, properly done, the plumbing isn't an issue.

    The same thing with your installation of the Kerdi and various components (Kerdi-band, various seals around penetrations, etc.). The major one is the pan...if it does not leak when filled nearly to the top of the curb during the flood test, when will there ever be the same water pressure and volume of water there? On the walls, where you may have any one of the approved boards, it's pretty simple to ensure you have at least a 2" overlap of the material. It's not really very hard to place the material properly.

    Your argument of poking holes in things comes down to workmanship...if you did it in the pan, what's underneath there may not be directly affected in the pan, but it would still affect the subflooring. You tear it, you fix it...once it is covered with tile, it isn't going to magically get a hole in it.

    On the walls, while nothing is impossible, it's much harder to poke a hole in things, and again, after it is covered in tile, how much ever really gets through the tile or the grout and into the thinset with any pressure? Almost none, and unless the shower is used 24/7 with a shower spray directed at it, it has the majority of the day to dry out towards the surface. Any bigger holes would hopefully be seen before they were covered up with tile. So, even a small puncture on the wall (which should have been fixed) has negligible chance of damaging anything. On the walls of a shower...how far do you think moisture penetrates underneath a tile on a surface membrane like Kerdi? You'll typically have maybe 1/8" of thinset covered with tile and grout...it can't hold much water, and with gravity, why would it be there in the first place? At your wall/pan junction, you have at least two layers of Kerdi assuming you seam it there, with at least a 2" overlap that was tested during the flood test and verified it didn't leak...why would that more vulnerable area leak?

    The example was given about cracking the el the shower arm is screwed into...certainly that could happen, but how often? Maybe when first installed, but then that's easy to check - cap the end, and turn the water on and listen.

    Same idea with the tub spout, should that be in question, although many of them do not use an el and a nipple.

    Water damage to the substrate in a properly installed Kerdi shower system is highly unlikely. Just like playing Powerball...there's a chance to win, but not a good one. The odds of a Kerdi shower failing is pretty low. IMHO, any leak in your shower needs repair, and if it does, that often entails some tearout.

    There's risk in any endeavor in life...the only ones you'll win on are that eventually, you will die. The risk in a properly built Kerdi shower is low enough to not be an issue IMHO. If you do not feel you have the skill to do it with drywall, fine by me.

    Properly built...they do not leak, everything stays dry, no problems. You'll likely have a roof leak damaging your drywall ceiling or walls before your shower.
  10. dhagin

    dhagin builder:anti-builder

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    Location:
    oahu
    what DonL said! :)
  11. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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    Post(s) deleted by John Whipple
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  12. johnfrwhipple

    johnfrwhipple Bathroom Design & Build - North Vancouver, B.C.

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  13. jim mills

    jim mills New Member

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    Location:
    nebraska
    What the hell is kerdi-koll. I thought they simply recomended using a non modified mortar with a 2" overlap to create a water tight seal?!?!
  14. eurob

    eurob master tile and stone installer

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    615
    Location:
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  15. eurob

    eurob master tile and stone installer

    Messages:
    615
    Location:
    Montreal
    [video=youtube;eexoFBEJG5I]http://www.youtube.com/watch?v=eexoFBEJG5I[/video]


    [video=youtube;t5bgmSVejkc]http://www.youtube.com/watch?v=t5bgmSVejkc[/video]
    Last edited: Jan 29, 2014
  16. DonL

    DonL Jack of all trades Master of one

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    Videos like the one above can cause Cooties on a V-Board Forum and a users computer, and should be avoided. It also slows the site down.

    A simple Link will work just fine.


    Just saying...
  17. eurob

    eurob master tile and stone installer

    Messages:
    615
    Location:
    Montreal
    You mean like this......

    [video=youtube;okGFj-4q2d4]http://www.youtube.com/watch?v=okGFj-4q2d4[/video]
  18. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    I think a lot of this comes down to expectations...

    In a conventional shower, one expects that some moisture will get through the cbu walls - not liquid, but moisture...we protect the vulnerable parts behind it with a vapor barrier (often plastic film or roofing felt).

    In a conventional shower, one expects the setting bed to get wet, and we provide a path for moisture to get out and use a material that won't be harmed by being wet (the mortar). We rely on using a waterproof liner and sealing it properly to the drain and where it was cut to cover the curb.

    We expect what's underneath the pan won't be harmed because of the waterproof pan.

    In a shower built with Kerdi, one expects that NO moisture will get beyond the waterproofing layer on either the walls or the pan. So, we expect it to successfully keep whatever is behind it perfectly dry.

    When the plumbing is installed in the house, we expect that it won't leak through the wall or ceiling onto our nice flat screen TV, or our photo book, or our artwork, or nice wooden floors or damage our walls. We also expect the same thing from our roof, windows, and doors and do not use any other protection for the drywall or objects in the rest of the house.

    All of the water that feeds the shower goes through those pipes on their way there, and often, much of the water that supplies other things in the home...all of those are feed with those pipes in the walls, ceilings, and floors, often with a second story beneath them...we do not expect those to leak.

    Why do we expect the pipes in a shower to leak and wet your substrate for your waterproofing? If you build your shower properly, neither the walls nor the floor will leak, so why obsess on what is behind or underneath them? If you're so worried about those, what about the stuff in the rest of the house...those pipes run by, over, and underneath them, too?
  19. eurob

    eurob master tile and stone installer

    Messages:
    615
    Location:
    Montreal
    We limit our protection to the tiled area -- especially showers , steam showers etc. -- , drywall behind it .... is not an option .

    If you build your shower properly ....you definitely need to be obsessed with what is behind and underneath them.
  20. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    22,139
    Location:
    New England
    Then, you do not trust that Kerdi can actually do what it says it can...provide a waterproof layer. If it failed on the floor, the subflooring would rot out and likely the studwalls around it. If it leaks on the walls (MUCH harder to do with gravity moving it down), then, and only then, would it be an issue. But, if it works for the pan, why wouldn't it work for the walls? A properly built Kerdi shower just does not leak.
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