Kerdi membrane install question.

Discussion in 'Shower & bathtub Forum & Blog' started by pete c, Mar 10, 2013.

  1. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    You either believe the testing and the manufacturer that Kerdi, properly installed, is waterproof, or you don't. Or, you don't trust your ability to do it right. If it is waterproof, as long as what's behind it is stable and is recognized to be able to hold and bond with thinset for a good seal, it's good (there are millions of tile installed on drywall outside of a shower, so drywall is known to hold tile and thinset well as it will hold onto Kerdi). If you don't believe this, don't use it! If you don't have confidence in the manufacturer, don't use it. If you don't trust yourself that you can do it, don't do it! Versabond is a modified thinset (lightly modified, but still modified). There's nothing wrong with using cbu, or adding other products that are known to be compatible on top of it to give you extra margin except for the costs (and starting with something else may work as well and be less if you're going to combine products). If you feel that extra margin is worthwhile, go for it, it's your house, may make you sleep better. Using a modified thinset voids your warranty, as Schluter specifies only the use of an unmodified when using this material. A worst case test will be the flood test. A shower does not normally have standing water in it, and if it does because of a bad drain or something similar, it typically doesn't stay there for the common 24-hours or more a flood test checks. Very little moisture normally gets below the tile in a normal shower, but it still needs to be managed, and if not, can accumulate and cause problems. With the slope on the pan, there should be no pooling of any possible moisture underneath the tile on top of the membrane. The sheet material is waterproof, a proper 2" minimum seam may wick a little water, but not beyond the full width, unless you have too much thinset in there (this is where the technique is important). But, even then, if you have the proper slope to things, there is no hydrostatic pressure to push water into that seam - the only time it would happen is during the flood test.
  2. muskymike

    muskymike New Member

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    6
    Location:
    Wisconsin
    I agree with Jim. I have done hundreds of Kerdi showers with drywall and have had 0 problems. If a reputable company recommends to use regular drywall behind their product use it. Besides drywall is way easier to cut than CBU and also less money.
  3. johnfrwhipple

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

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    Should you flood test showers built with Kerdi? Yes

    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  4. muskymike

    muskymike New Member

    Messages:
    6
    Location:
    Wisconsin
    I don't need to flood test it because I know it won't leak. You can do your showers how ever you want. I will do the same. Besides if I ever did have a problem I know that Schluter would stand behind me on it and if one of the showers was to leak I would have had a phone call. I will always recommend using drywall behind Kerdi. You can recommend what ever you want.
  5. johnfrwhipple

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

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    Are you required to flood test Kerdi Showers in Springbrook, Wisconsin? Answer is Yes

    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  6. muskymike

    muskymike New Member

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    And now we know why you were banned from our site. Surprised Terry hasn't banned you.
  7. johnfrwhipple

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

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    Polk and Barron County - Plumbing requirements (flood tests)

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    Last edited: Mar 15, 2014
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    Kerdi has been around for a long time, many showers installed with it. Most local inspectors will look at the certification from an independent lab and the manufacturer's installation instructions and, if those are followed accept it. If yours doesn't don't fight them, you'll lose either time or money and it's not worth the aggravation. If you take the time to read the certification document I'm linking to http://www.icc-es.org/reports/pdf_files/ICC-ES/ESR-2467.pdf, you will see that it was both tested and passed with the use of drywall in a shower. It also passed with other backer materials. Any of those work, your choice, since the certification covers all. The manufacturer indicates in their installation instructions their preference for drywall as the easier, less costly installation media. You are not required to use it, but if installed per the instructions, it is fine.
  9. johnfrwhipple

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

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    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  10. pete c

    pete c New Member

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    Location:
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    I kind of like that Ardex stuff. I was thinking putting it over the kerdi along seams and corners might be a worthwhile bit of insurance. Does it apply over Kerdi OK?
  11. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
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    Location:
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    It works fine over Kerdi. Do you need it? Not if you build it properly. Does it hurt? No, except for more time and money. Your house, your money, your time. It's a belt and suspenders thing...your choice.
  12. johnfrwhipple

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

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    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  13. johnfrwhipple

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

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    Kerdi Coll - Ardex 8+9 - Can you see the difference?

    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  14. pete c

    pete c New Member

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    Location:
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    I now have most of the kerdi up. Kind of wish I had gone with the cement board as I don't trust my seaming abilities. I am going to go with ardex over them for a little insurance.
  15. pete c

    pete c New Member

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    Location:
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    So kerdi col and ardex 8+9 are more or less the same thing? Is there a price difference? If not, I guess I will use the col as I can get it where I bought the kerdi membrane.
  16. johnfrwhipple

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

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    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  17. pete c

    pete c New Member

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    Location:
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    I've seen ardex 8+9 About 80 bucks. I guess that is the way I'll go. Thanks for the hand mixer tip. I'll just have to do it when the wife is out of the house. She'd kick my ass if she caught me doing that!
    Last edited by a moderator: Dec 26, 2013
  18. johnfrwhipple

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

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    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
  19. pete c

    pete c New Member

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    Location:
    CT
    Update.

    On john's advice, I went ahead and ordered the ardex 8+9 for a little insurance. Very nice product and mixes well in small batches with the OL's sunbeam handheld mixer.

    Glad I did.

    The stuff rolls on kind of sticky as a second coat. So sticky that in one area it actually started to pull the kerdi away from the drywall.

    This was one of the first wall pieces I installed. Being a newb, I made two mistakes. First off, I tried to use large sheets around corners. Bad idea. They use smaller pieces on individual walls for a reason. It is a PITA to try to go around inside corners. Outside corners seem fine. Second mistake was using big box store Mapei thinset to begin with. The second bag was mapei from my tile dealer. Night and day difference. Same price. The more I shop at real stores, the more I loathe Lowes Depot!!!!

    Sure wish I could backup a few months and do this damn job the old fashioned way, using cement board. The way I originally intended to do it before I let a Kerdi salesman get ahold of me. :mad::mad::mad:

    So, where do I go next? Do I consider this a rather expensive lesson, rip it out and start over with CB and ardex overcoat? Or, do I assume that I did a decent enough job on the rest of the kerdi, repair that section and tile away? The rest does seem to be adhering well.

    To repair, my plan is cut away the bad section, install new kerdi and ardex over it. Is it possible to cut out a section which is about 2 ft square, clean it off and reinstall? I am out of kerdi. I actually was able to return the unused half roll, contrary to what some said. I do have enough band left to seam it.
  20. johnfrwhipple

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

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    Post(s) deleted by John Whipple
    Last edited: Mar 15, 2014
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