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Thread: Proper Installation of Kerdi Band?

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    Default Proper Installation of Kerdi Band?

    First off, I want to say,"Hello!". My name's Jeff C. and I'm new to these forums (albeit I've surfed them many times in the past several years). The reason I'm posting, is because I have huge dilemma, and you're my last hope (pretty much). I'm more than 3/4 through with a reno of our Master bath, and have reached an impasse as far as how to finish the gap between the concrete backer board (HardiBacker 500), and the tub edge. Here's the layout of the job:
    1. Tub is going into a 3 wall alcove with one of the three walls being an exterior wall w/a window in it
    2. Tub (a Kohler Hourglass 1219-L; free standing with integral tile-flange, and no apron as I'm framing a knee-wall and tiling it instead)
    3. .6 mil plastic sheeting over the studs (in hindsight, if I had found these forums earlier in the project, I would have just used RedGard or a Noble product, and I probably wouldn't need to ask for further guidance, but que sera, sera)
    4. As mentioned above, HardiBacker 500 on walls installed with the recommended screws (1st course is already up, and taped)

    Ok, so the install instructions do say to bring the CBU over the flange, but due to that one window on the exterior wall (not to mention a huge pita), shimming the studs out any more than I did (1/4") was just not feasible. Sooooo, I'm trying to make the best of the current situation by "adapting to my environment". Which brings me to a couple of questions:
    Q1: I know that waterproofing the seam between the CBU and the tub is a crucial one to get absolutely correct, so I plan on using Kerdi-Band, with Kerdi-Seal, to tackle this seam. But, I'm not sure how I should install the Kerdi-Band. The install instructions say to bed it in thin-set on the outside of the CBU, but I'm wondering if this will have a detrimental effect due to the 6mil plastic already installed over the studs, under the CBU (the whole "two waterproof layers trapping moisture" thing) The other alternative is to install the Kerdi-Band behind the CBU, but if that's the proper installation method (in my case), should it go on top of the 6mil plastic, or underneath it?
    Q2: I've seen it mentioned, by one knowledgeable person on these forums, that "the tub should be filled with water before pinning it to the studs". Is that correct? (as I was under the impression that it should be filled with water/weighted down, prior to caulking, but have never heard filling it before screwing/nailing it to the studs.) If it's recommended that it should be filled/weighted down prior to nailing it to the studs, how is that accomplished? I mean, how would I prevent a 500+ lb tub from shifting around, off the shims, and/or potentially ruining the entire drain structure or whatever?
    This reno is going on over 5 years now (my wife has been very understanding, but her patience has run out) and has hit a serious snag (because I'm scared as hell at messing it up at this point). ANY help/opinions/intruction will be soooooo appreciated that I may name a grandson after the person that guides me in the right direction ... Thank you, thank you, thank you, in advance !!! .... Jeff C.

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    If you are going to use a surface waterproofing, then I suppose you could use the Kerdiband there, otherwise, I do not think I'd use it at all. With the plastic behind, and Kerdiband, any moisture that may penetrate the cbu would be trapped. The beauty of a surface membrane is nothing on the entire wall behind it gets wet. In what you have, the cbu can wick some moisture, but the plastic film behind it protects the studs. The tiling flange (if your tub is level!) keeps water from sloshing into the walls from the rim, and the tile prevent major moisture from getting to the cbu in the first place, so it only has to dry a little, since it never gets very wet in the first place.

    Now, if you wanted to use the Kerdi system and waterproof the walls, Schluter has some diagrams on their website that describe how to do that. You'd use some KerdiFix to seal the Kerdiband at the tub wall junction, and thinset on the Kerdi/Kerdiband to waterproof the seams going up the wall.

    There are probably some hybrid systems you could use, but you wouldn't have a warranty. Lots of tub/showers work and last with the plastic sheet draped over the tiling flange, tile and caulk at the tub/wall junction. As said, though, if the tub isn't level, and water pools or flows back rather than into the tub, those can be problematic.
    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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    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Default Full topical water poofing approach

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    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Default Kerdi Band to back side of board.

    Post(s) deleted by John Whipple
    Last edited by johnfrwhipple; 03-15-2014 at 02:43 PM.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    FWIW, my definition of hybrid install is any set of products not installed in accordance with the local distributor's instructions...many of the products are designed as a system, and have unknown and possibly (not definitely) unknown characteristics and performance when not installed as designed. John likes to do his work his way, which in my definition (and the manufacturer's) is a hybrid system.
    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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    Post(s) deleted by John Whipple
    Last edited by johnfrwhipple; 03-15-2014 at 02:43 PM.


    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

  9. #9
    Retired Defense Industry Engineer jadnashua's Avatar
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    Quote Originally Posted by johnfrwhipple View Post
    More useful information from a Retired Defense Industry Engineer - that sure clears things up
    The point being...if a manufacturer has a system that works, it is best to use it, and install it properly. Mixing systems is not necessarily going to improve the end result, and may lead to failures that are unanticipated. The manufacturers design and test things, and have a vested interest in preventing failures but those only apply if they are used as designed. You can 'get away with' combining products sometimes, but you are on virgin territory most of the time, and have a sample of one or few to determine if it is actually going to work. You get the same arguments with most things...the comment "I've been doing it that way for years and never had issues" comes up often. And, things may work fine that way, but just like in the codes, where stuff that used to be done worked most of the time, newer codes were written to handle the 'what if' situations, the old methods just couldn't handle. There, especially, you get comments like "but it worked fine, why should you change it now?" come up. The manufacturer is the one that has the experience and depth of engineering to determine how their products perform, and how best to use them to provide a suitable result.

    What the OP started with was a fairly typical tub/shower install. Don't remember a window being discussed in the initial question. Those require special consideration in a major wet area like a shower, and I'd not feel comfortable trying a conventional waterproofing/moisture control method there which is what you've started. I'd much prefer a surface membrane since I feel it is more reliable, especially when dealing with a window.

    Otherwise, when using a surface applied waterproofing, it should be all or nothing, especially if you have plastic film behind the wall already. Adding some on the surface at the tub/wall junction will trap moisture there. If you can prevent any moisture from penetrating the wall entirely, as a surface membrane does, it's not a big deal - the cbu should never get wet IF you waterproof it properly. THere's a big IF there, which is why having something behind it as well as on it can be an issue. The only good thing about cbu in this case is that it does not degenerate if it does get wet.

    One reason why I'm proud of having working in the defense industry is that it forces a mindset to consider all of the 'what if' situations. You don't get a second chance in trying to detect an enemy's missile attack, or to shoot down an offensive missile or target intending to rain harm on you. IOW, you have to do it right the first time, and consider how to make sure it is highly reliable...this is a mindset, ingrained from years of work that carries over to other aspects of life. Innovation helps, you have to stay ahead of the enemy. In the case of a shower, the enemy is moisture, and controlling it is critical. It has to be done right, and mixing systems is risky, as they each approach the solution from a different viewpoint and methodology, and they don't always get better with picking and choosing parts of each system, or, as one here likes, to build one on top of the other. Best to stick with one and do it well.
    Last edited by jadnashua; 12-24-2013 at 10:20 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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    First off gentlemen, thank you sooooooooo much for replying so quickly. I (and I'm sure my wife) truly appreciate it. I should have been more specific in my initial post, when I mentioned the window. The window is not actually in the tub/shower alcove, but rather about 2' outside of it above the toilet. The reason I metioned it at all was to infer that partly because of the window, shimming out the studs in the bath alcove, any more than I already have (1/4"), would be too big a pita. My tub alcove is pretty much like yours John (as seen in the photos of the tub at your house), except I don't have any soap/shampoo/etc. recesses built into the walls, and the wall opposite the tub/shower plumbing and drain is an exterior wall (insulated with non-faced R13 to prevent moisture being trapped in the wall). I had read the past post you referred to (about the install with the window that's actually in the shower. As shown in those other pics that you included) I believe that after looking at the new pics you posted (of the install in your own house) the solution to my dilemna is as follows:
    1. Pin tub to tub alcove wall studs (I know that the nails should not be driven tight to the tub flange, but rather have just a slight bit of "wiggle room". But, as per question 2 of my initial post, I'm still uncertain as to whether I need to fill the tub before pinning it to the studs)
    2. Attach KerdiBand to tub alcove wall studs, like you did in your photos, allowing bottom edge of KerdiBand to overlap tub flange (I'm going to overlap the height of the flange plus 1/2" to 1" extra, then after sealing the seam, trim the excess)
    3. Overlap the KerdiBand with my 6 mil plastic vapor barrier (KerdiBand under w/plastic over) by maybe 2-3", then trim excess 6 mil sheeting (this will create a shingle-like effect)
    4. Bring CBU down to 1/8" above tub tile flange, then using KerdiFix to adhere KerdiBand to tub flange
    5. Install the ceramic tile I'm using on the walls in the tub area, and finish off the tile to tub seam with silicon caulk (where tile meets tub deck)

    Does that sound plausible John?? And again, thanx in advance ...

  11. #11
    Retired Defense Industry Engineer jadnashua's Avatar
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    Sounds like a plan. Kerdifix is really good stuff, and will even seal underwater...got a small hole in a pool liner...no need to drain, it will seal a patch fine. You don't need both the Kerdiband and the plastic film behind there, but for that small distance, it won't hurt, and the Kerdiband is tougher than the plastic film, so it would be harder to tear. While cbu isn't affected by being wet, my preference is to never allow it to get wet in the first place, which is why I prefer a surface applied membrane. THen, there's also less to ever dry out. But again, ensure the tub ledges are level - you do not want water pooling, you want it to be able to drain off that shelf or all run to one end (or out into the room!).
    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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    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Default Temporary Shower Dam - Installation of Kerdi Band - Photo(s)

    Post(s) deleted by John Whipple
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    jfrwhipple@gmail.com - www-no-curb.com - 604 506 6792

    Always get construction advice double checked by your local city hall. Flood Test Every Shower - Every Time.

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    Gentlemen, sorry it took me so long to reply back to the thread. In addition to a busy holiday season, my mother passed away shortly after New Year's. It's been a hectic several weeks to say the least. John, in answer to your questions:
    Q: What brand of backer board are you using?
    A: HardiBacker 500

    Q: What size mesh tape will you use to tape the backer board seams?
    A: 2", self-adhesive, alkali-resistant, fiberglass mesh, cement-board tape

    Q: Do you have blocking in all corners of the backer board sheets?
    A: Yes, extra framing was added where needed, and the manufacturer's installation instructions were followed exactly (http://www.jameshardie.com/homeowner...install-us.pdf). I also added 2x4 blocks in between all studs (except for the span, between the studs, where the mixing valve/bath plumbing prevents it), to not only give me more usable area in which to pin the tub to the walls/studs, but to also give me a solid, level surface to brace the KerdiBand/Poly-to-tub seam.

    ** Your install as described is on small step above bare minimum code. Make sure the steps I mentioned above get done.
    The steps you mentioned will get done (much to my wife's consternation, I give the term anality new meaning), but I must ask something. If the install method I described (entire bathroom covered in 1/2" green-board, except the shower/bath nook that has HardiBacker 500 on the walls, and green-board on the ceiling. Extra framing was added in the ceiling to allow green-board to be screwed 12" O.C. as per code. 6mil poly sheeting installed over studs as vapor barrier (with un-faced insulation used above the tub-flange area, and paper faced insulation used below the tub-flange area, on the one exterior wall), with all staples/any holes siliconed over to maintain structural/waterproof integrity. In addition, a small squirt of silicon was shot into each screw hole before screwing to studs so as to maintain structural/waterproof integrity. All cement board seams in the alcove were/or will be siliconed in a way that ensured additional waterproofing properties, but not so as to impede the adherence of the cement-board tape, or the thinset used to seal the taped seams (in other words, neither the tape, nor the thinset, comes into contact with the silicon behind the seams). The tube will be set in a bed of mortar/cement, leveled << shimmed as needed with a generous amount of construction adhesive under the tub-feet blocks >>, then pinned to the studs with S/S Truss-head screws. As per your instructions, the cbu-to-tub flange seam will be finished with 7" KerdiBand attached to the studs, then the 6mil poly trimmed, run over the top of the KerdiBand << I'm going 2" down from the top of the KerdiBand >>, trimmed, and sealed with Kerd-Fix. Then the KerdiBand will be brought over the tub flange, trimmed to length, and sealed to the tub flange with Kerdi-Fix. Finally, the last course of cbu will be put up, and brought down to within 1/8" of the top of the tub flange. All seams will will be taped with the cement board tape, and finished off with modified thinset. It will be all be finished off with tile.) is "one step above minimum code", then what would "over and above code" entail? Especially if waterproofing products like RedGuard, Nobel etc. are not being used?

    Q: The exterior wall - do you have the vapor barrier down to the bottom plate prior to setting in the tub?
    A. No, the 6mil plastic vapor barrier is over un-faced fiberglass insulation above the tub flange area, but below the tub-flange area, paper-faced insulation was used on the exterior wall, thus eliminating the need for the plastic sheeting.

  15. #15

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    Quote Originally Posted by jadnashua View Post
    The point being...if a manufacturer has a system that works, it is best to use it, and install it properly. Mixing systems is not necessarily going to improve the end result, and may lead to failures that are unanticipated. The manufacturers design and test things, and have a vested interest in preventing failures but those only apply if they are used as designed. You can 'get away with' combining products sometimes, but you are on virgin territory most of the time, and have a sample of one or few to determine if it is actually going to work. You get the same arguments with most things...the comment "I've been doing it that way for years and never had issues" comes up often. And, things may work fine that way, but just like in the codes, where stuff that used to be done worked most of the time, newer codes were written to handle the 'what if' situations, the old methods just couldn't handle. There, especially, you get comments like "but it worked fine, why should you change it now?" come up. The manufacturer is the one that has the experience and depth of engineering to determine how their products perform, and how best to use them to provide a suitable result.

    What the OP started with was a fairly typical tub/shower install. Don't remember a window being discussed in the initial question. Those require special consideration in a major wet area like a shower, and I'd not feel comfortable trying a conventional waterproofing/moisture control method there which is what you've started. I'd much prefer a surface membrane since I feel it is more reliable, especially when dealing with a window.

    Otherwise, when using a surface applied waterproofing, it should be all or nothing, especially if you have plastic film behind the wall already. Adding some on the surface at the tub/wall junction will trap moisture there. If you can prevent any moisture from penetrating the wall entirely, as a surface membrane does, it's not a big deal - the cbu should never get wet IF you waterproof it properly. THere's a big IF there, which is why having something behind it as well as on it can be an issue. The only good thing about cbu in this case is that it does not degenerate if it does get wet.

    One reason why I'm proud of having working in the defense industry is that it forces a mindset to consider all of the 'what if' situations. You don't get a second chance in trying to detect an enemy's missile attack, or to shoot down an offensive missile or target intending to rain harm on you. IOW, you have to do it right the first time, and consider how to make sure it is highly reliable...this is a mindset, ingrained from years of work that carries over to other aspects of life. Innovation helps, you have to stay ahead of the enemy. In the case of a shower, the enemy is moisture, and controlling it is critical. It has to be done right, and mixing systems is risky, as they each approach the solution from a different viewpoint and methodology, and they don't always get better with picking and choosing parts of each system, or, as one here likes, to build one on top of the other. Best to stick with one and do it well.
    Most of these are true, however old methods work very well vs. the new methods(codes) -- 2" vs. 1 1/2" for showers , etc. --.

    Usually most of the mfg recommendations are important when warranties are in play , but nobody talks about the situations -- at least openly -- where the products fail. What you get is -- read the fine printing or you are the only one with this sort of failure or etc. --. Nothing is an absolute , but for the intended recommendation , for a DIY , stick with the printed literature from the mfg. Check it often or save a copy of it at the same date as your project is completed.
    Last edited by eurob; 01-16-2014 at 05:36 AM.

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