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Thread: Can I Use Any Thin Set With Kerdi? The ICC-ES Evaluation Report On Kerdi Says You Can

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Default Can I Use Any Thin Set With Kerdi? The ICC-ES Evaluation Report On Kerdi Says You Can

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    DIY Senior Member BobL43's Avatar
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    does this qualify as a conundrum or a dilemma?
    I am definitely not a pro plumber, but I am a pro crastinator

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by johnfrwhipple View Post
    I got Eric from Noble company shedding some good light onto the problem over on Contractor Talk. Eric mentions that drywall was removed from the TCNA book years ago so I guess we know Jim's copy is outdated and Eric also mentioned that you can get what ever kind of report you want but the code is the code and with TCNA, ANSI and TTMAC drywall is not listed.

    That is not what bugs me. What bugs me is do I use regular non-modifed thinset to install ditra on plywood or can I use any thinset for ditra or Kerdi. And further more do I need to use the Kerdi Flex to seam my Kerdi sheets. We always use Kerdi Band or scraps of Kerdi or overlap the Kerdi itself.

    Crazy that the ICC rules need to be followed verses the Schluter rules.

    http://www.icc-es.org/reports/pdf_fi...S/ESR-2467.pdf

    Jim should know - they must discuss this at the lunch table

    JW
    I'm still trying to decide which matting to use; Ditra, Spider Web or the Noble Seal TS. I thought that modified, like Versabond was fine to use to bond the Ditra to plywood. According to what you just wrote, that is up in the air now too? One you did not mention (for tiling over plywood) is Tavy thin skin and his glue. Would you rather me start another thread on that?
    I am definitely not a pro plumber, but I am a pro crastinator

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The installation instructions are referenced and cover this.

    Bonding Ditra or DitraXL is dependent on the substrate it is going over: they call out modified to bond it to a wooden subfloor and (I think, I'd have to reread the manual, either modified or) unmodified over masonary materials...it's pretty clear. Since Ditra is only spec'ed for floors, and the deflection issues and movement issues with wood are the biggest unknown, the use of a modified is called for, espcially since there's a moisture release path, both through the substrate and by the open channels of the membrane itself, out to the sides.

    They call for unmodified when installing Kerdi, both under and over, and unmodified on Ditra over as there's no good moisture migration path between the tile and the waterproof membrane.

    If you want to deviate from this, they say you need to call both them and the material (likely tile) manufacturer to come up with a suitable solution, if there is one. I have heard, indirectly, that they've allowed a rapid set modified when asked. Rapid set mortars are not likely a good solution for a DIY'er because of the limited pot life.

    IF you want Ditra or Dita XL to be waterproof, then you need to band the seams, just like you do with Kerdi and that calls for an unmodified, since it is on top of the membrane. This may call for two different thinsets, or the same one and mixing it with either water or their addative to make it into a modified (probably the simplest since you don't have extra thinset in the wrong configuration - you make it up to need as required).

    This is all called out in the manual. The key is: suitable and per the manufacturer's instructions.
    Last edited by jadnashua; 12-19-2011 at 08:12 AM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    DIY Senior Member BobL43's Avatar
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    Quote Originally Posted by jadnashua View Post
    The installation instructions are referenced and cover this.

    Bonding Ditra or DitraXL is dependent on the substrate it is going over: they call out modified to bond it to a wooden subfloor and (I think, I'd have to reread the manual, either modified or) unmodified over masonary materials...it's pretty clear. Since Ditra is only spec'ed for floors, and the deflection issues and movement issues with wood are the biggest unknown, the use of a modified is called for, espcially since there's a moisture release path, both through the substrate and by the open channels of the membrane itself, out to the sides.

    They call for unmodified when installing Kerdi, both under and over, and unmodified on Ditra over as there's no good moisture migration path between the tile and the waterproof membrane.

    If you want to deviate from this, they say you need to call both them and the material (likely tile) manufacturer to come up with a suitable solution, if there is one. I have heard, indirectly, that they've allowed a rapid set modified when asked. Rapid set mortars are not likely a good solution for a DIY'er because of the limited pot life.

    IF you want Ditra or Dita XL to be waterproof, then you need to band the seams, just like you do with Kerdi and that calls for an unmodified, since it is on top of the membrane. This may call for two different thinsets, or the same one and mixing it with either water or their addative to make it into a modified (probably the simplest since you don't have extra thinset in the wrong configuration - you make it up to need as required).

    This is all called out in the manual. The key is: suitable and per the manufacturer's instructions.
    Thanks Jim, I did download and read the manual a few weeks ago, but can't seem to remember anything about using their own additive. going to re-read it again. This sounds like more art than the science it should be to me. And maybe that art is in the form of BS
    I am definitely not a pro plumber, but I am a pro crastinator

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Retired Defense Industry Engineer jadnashua's Avatar
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    John, you're not interpreting it correctly. They state: 'The membranes are separated at expansion joints to avoid restriction of the joint movement, and the seams are sealed with flexible KERDI-FLEX.'

    Got a crack in the floor? Need to keep it waterproof? Butt the DITRA seams and seal it with KERDI-FLEX. Build a shower: read section 3.4.1 again...it calls out Kerdi-Band for waterproofing the seams.

    Determine acceptable backer boards? Read section 2.0, it lists gypsum board. This is from August 2011, not old, although they also did a test on it a long time ago. The test reports are not valid forever.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by BobL43 View Post
    Thanks Jim, I did download and read the manual a few weeks ago, but can't seem to remember anything about using their own additive. going to re-read it again. This sounds like more art than the science it should be to me. And maybe that art is in the form of BS
    Most thinset manufacturers offer an addative that can be used with their dryset (unmodified) thinsets. WHen you use this addative, it essentially becomes a modified thinset. You use that instead of water when mixing the thinset up. It is not a Schluter thing...it is entirely a thinset manufactuer thing. If your job might require both types, you can stock up on the unmodified and the addative, then, by choosing how you mix it (add water for unmodified or the addative/admix) and you get a modified). This can simplify things for you. There's nothing in the Schluter installation manuals about this, they only state what type to use, not how you obtain it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Retired Defense Industry Engineer jadnashua's Avatar
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    The report specifies following the instruction manual...the manual specifically identifies which thinset is required. Unmodified for Kerdi, and surface dependent for Ditra. One thing to keep in mind with Ditra is that on the top of it, the thinset only has to hold the tile...it does not bond to the membrane, and, because it can't outgas to dry, they specify an unmodified on top. On bottom, depending on the substrate, you may have up to two paths for drying: one through the channels created by the waffles and another through the surface. The 'pillars' that form when you fill the dove-tailed waffles lock it into the membrane, and hold the tile up. The sizing of the waffles is such that to get a minimum of three pillars, you need at least a 2" tile (thus the restriction in the manual when using Ditra as to minimum tile size - the pillars form the vertical support structure).

    I'll go back to my example from another time: is 1/8" glass any less waterproof than 1/2" stuff? Then, consider that it is OVERLAPPING the underlying material, so it is essentially adding to the thickness of the SYSTEM and doesn't stand alone. Kerdi installs must be taken as a SYSTEM, made up of correctly applied parts.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    In the Trades mtcummins's Avatar
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    Quote Originally Posted by johnfrwhipple View Post
    So to get back to your discussion about drywall.

    If you use drywall and Kerdi and then seam your sheets of Kerdi with Kerdi - Flex your good to go. That is the proper procedure.

    JW
    Did I just hear John say that drywall in a shower is proper given a proper installation? Did hell just freeze over?

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    ACO Shower Drain Sales johnfrwhipple's Avatar
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    Post(s) deleted by John Whipple
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    Retired Defense Industry Engineer jadnashua's Avatar
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    The best thing is to not mud the walls before applying Kerdi. The thinset and the membrane works great to fill minor (nail/screw) holes and fill the tapers of the boards or joints. I'll try to get a read on what works, and if I do, I'll report back. My personal feeling is, if it is a small area, you have virgin drywall around it, and the tile is fairly large, it's not a big thing since even if the moisture from the thinset does soften the stuff, once it dries, it's good, and the whole area around it is tight in the interim. Now, on a large area like a seam, it could be a problem best averted by not mudding in the first place.

    Being a holiday weekend, responses will be delayed, but I would think that this, for example would work fine: http://www.custombuildingproducts.co...er=arc&lang=en

    Every thinset manufactuer sells a laytex primer for its SLC, and similar products that improves the bond and seals the underlying materials so the cement products will stick better.
    Last edited by jadnashua; 12-24-2011 at 03:02 PM.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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