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jayjonbeach 04-16-2021 02:49 PM

Steam Room waterproofing technical questions
Hi all. I did a fast search for this and did not find any results. Its going to be a steam shower application, mortar bed, Laticrete Sheet membrane and flange drain.

What do YOU do when installing this for bonding to the flange?

I've seen conflicting info for this, as the issue that some worry about is the adhesion of Thinset to a smooth PVC surface of the flange, and probably why Shuter put a fleece on theirs (which de-laminates if submerged btw...).

Options appear to be:

- Scuff the surface with fine sand paper and just use Thinset over the flange under the sheet membrane

- Scuff the surface with fine sand paper and put some liquid Hydroban on the flange first, then use Thinset over that and membrane over that.

- One of the above but no scuffing the surface

With a smooth surface delamination seems like a real concern over time

Thanks for your thoughts

John Bridge 04-17-2021 09:58 AM

Welcome aboard, Jon. :)

I've never used the Laticrete drain, so can't help much. I think I would be in the roughing up school, though. A good quality thin set should work, but I would probably go with something like PL-100 out of a caulking tube. :)

jayjonbeach 04-19-2021 10:27 AM

Thank you John, I do find it odd why a manufacturer wouldn't at least put some small ridges or the like on there to help bonding.

Hoping for some experienced with working with this drain will chime in what they think

John Bridge 04-20-2021 08:00 AM

Jon, have you tried calling Laticrete? They've got some excellent advisors. 800-243-4788 :)

Lou_MA 04-20-2021 11:21 AM

Jon last I had read in the drain TDS you need 2 coats Hydroban, properly applied, on drain flange. Let dry then thinset sheet membrane to it.

jayjonbeach 04-21-2021 01:48 PM

Thanks guys. @John yes I have at least twice, I think both times they said just thinset over the drain is okay, though one person said either would be fine, but in all cases no scuffing was recommended. Also see below:

@Lou thank you Lou I did see that on the sheet and it adds to the uncertainty I think, given what they are saying on the phone. Where I found it on the sheet it is describing a liquid membrane flooring waterproof application which then makes sense, but in my case I need to use the sheet membrane as it is a steam shower and their liquid is not yet rated for steam "perm"-wise.

Still a little torn, probably both ways are fine, but if push comes to shove in a slow leak failure situation I'm not sure the adhesion in either case to that smooth surface would hold up, maybe it does though not sure

jayjonbeach 04-21-2021 01:59 PM

Mapei Aqua Defense over Kerdi membrane seams (2" overlap exposed Thinset spots)
Hi all. I know, I know, it is not recommended or "required", in their opinion, I want to hear your opinions.

I hope we can agree Thinset is not waterproof. All these 2" overlaps rely on the perfect application of Thinset which is granular, even smoothed out close to perfect it has been shown that water can weep through the thinset, and more than the 1/4" max some say it should.

After deeply researching this for the last 2 months and watching many failure videos I just feel like putting liquid water proofing membrane over the 2" overlap seams, especially where thinset is exposed makes perfect sense and would keep it more waterpoof, especially in the case of a slow leak failure.

Is anyone out there doing this? What are your thoughts?
For the average shower, that does not fail, and so not a submerged application, probably 1/4" is all that would happen. I am doing a steam shower though, which kind of is a submerged application.


cx 04-21-2021 02:50 PM

Welcome, Jon. :)

I've combined your first two threads on this steam shower so folks can see what you're working on and what's been previously asked and answered. A moderator can give it a more generic title any time you'd like to suggest one.

My recommendation would be for you to chose one product or system and use it per the manufacturer's instructions for the best result.

I think there is some confusion on the requirements for water/vapor-proofing such steam showers. The ceramic tile industry standards require a direct bonded waterproofing membrane with a perm rating of 0.05 or better for a continuous use steam shower. When that rating was agreed upon, no companion requirement was specified for residential or non-continuous steam showers. In past, a perm rating of less than 1.0 was considered a vapor barrier in the construction industry and I would personally consider that sufficient for a residential steam shower. See my warranty information below.

The industry also allows membranes that do not meet the .05 perm standard to be used in continuous use steam showers so long as an additional vapor retarder membrane is used behind the wallboard. I think that a terrible standard, but I was not invited to vote on the measure.

For your shower you could use either the Laticrete membrane or the Kerdi membrane and feel confident of success if you comply very strictly to the installation instructions. If you start modifying and "improving" their materials or methods, it becomes a KMAGYOYO kinda situation.

My opinion; worth price charged.

jayjonbeach 04-23-2021 10:37 AM

Hi and thanks CX. I was worried you might combine the different topics, and as we can see, the result speaks for itself. Having been a Mod for many a forum myself I understand the inclination to try to keep it "organized", but combining 2 completely different topics (advice on one, vs advice on another) didn't make sense to me that is why I posted a separate thread for it.

So of course, I am trying to decide between these 2 systems, not thinking of combining them, and was hoping to get some real world reports of people doing these things and their opinions on it, manufacturers aren't always right, that is why they eventually have many product or technique "updates".... :)

To clarify, it is my contractor who is going to use AD over Kerdi because he says this is what they normally do, and I already expressed the logic of why I agree with him above, and others who I have seen do similar things, given the channeling that can happen if submerged.

My original idea was to go with Hydroban since they have their own liquid membrane, and I called Laticrete about putting liquid Hydroban over exposed Thinset and while they said it is not required (of course) I also got their blessing to do it. My installer is willing to use Hydroban, but typically always uses Kerdi, so of course is more comfortable using Kerdi and I am not sure has ever used Laticrete. So this makes the decision a little tougher now.

As far as warranty, I think we all know the chance of getting one is probably 1%, so pretty much everyone is KMAGYOYO anyway as actual product failures are fairly rare and typically hard to prove

I agree about the moisture sandwich, its not something I am considering no matter which membrane or wallboard I go with.

PS - at this point I think it would be helpful to change the title to "Mapei Aqua Defense over Kerdi membrane seams (2" overlap exposed Thinset spots)", it appears I can no longer do it

jadnashua 04-23-2021 04:07 PM

Way back when (and it still may be going on), at CTEF (ceramic tile education foundation) training sessions, they'd take a carboard box, then using thinset and Kerdi, cover the inside of it. The beginning of each day, they'd fill it with drinks and ice. By the end of the day, they were swimming in ice water. Over several months, the cardboard would start to break down...not from getting wet, but from the constant bending from the water load inside it, and they'd make a new one.

One has to install things properly, but when they do, there's no reason to second guess and use belt and suspenders to get the job done...that only adds to the chances of failure and the expense and time it takes to perform those unnecessary steps.

The stories you might read about failures are generally attributed to poor workmanship, or the incorrect materials...not material failures.

jayjonbeach 04-23-2021 05:40 PM

Hi Jim. Let us know where you think he did something not according to Kerdi's instructions here, because other professionals and myself aren't seeing it. This is one of many tests that were done


jadnashua 04-23-2021 09:38 PM

Whenever I've seen the Schluter guys install Kerdi, when embedding the material, they end up squeegeeing some thinset out whenever they get to an edge. I noticed during the video, that the installer usually stopped at about the edge of the membrane, and if you look carefully when pulling an edge back, right at the edges there were some small areas not covered. That could easily have been filled in with subsequent activities, but any small gap over time could let moisture penetrate. Kerdi works when you have fleece to fleece contact, filled in with thinset. An excess of thinset without the fleece layers in contact will wick moisture.

Another thing that they stress in their classes is how important it is to wipe the surface with a wet sponge prior to spreading the thinset to ensure that it doesn't get moisture sucked out of it, making it stiffer than desired when then trying to embed the membrane. That would affect how fluid it is, and maybe end up with it being a bit thicker layer and preventing the fleece to fleece contact. That's only important when going over the drywall, as the fleece itself won't suck moisture when adding the banding, but could be an issue where there already was some thinset from the previous step...best to have fresh stuff whenever you're embedding stuff. YOu also see them use a sponge to clean up excess thinset, but maybe that's just for esthetics rather than function.

From what I was told, Schluter in Plattsburg had a tower lined with Kerdi, then filled with water in their lobby for a time...it never leaked and the water pressure from the tower was more than you'd ever see in a shower (about 0.43#/foot depth).

I've not used the Laticrete drain. The surface may specifically be treated or manufactured to accept thinset. Keep in mind that when thinset cures, the way it gets its bond is because the cement grows crystalline spikes that interlock into any microscopic imperfections in the surface. And, that process continues past the nominal 28-days the cement specs use for testing strength, but by then, their growth curve is almost flat. IOW, the bond will continue to get stronger and the density will increase, which increases the water tightness of the seams (and any tile attached later in the process).

jayjonbeach 04-24-2021 05:57 PM

Thank you Jim for taking the time to look at that video and respond. I am sure you are pretty tired of folks like me pointing to the flaw in the German logic and then having to reiterate each time why it should work, if installed to 100% perfection :deadhorse: (and I have seen you in past discussions here and even other websites on this topic). I did notice what you pointed out to some degree, and I can agree that: Those small spots were most likely covered in after through his meticulous (he was really careful in this one since there was some similar criticism in his prior 4 tests, which all had the same result) additional troweling over all the edges, and normally in order to ensure 100% coverage or close to it, there is only one sure way to do that which is exactly what you described, squeezing some thinset out of each edge (which he was much of the time). Not doing that would mean almost 100%, that you either have too much or too little thinset under the membrane, at least in my mind, but of course pros doing this for 20+ years like Isaac in the vid can get pretty consistent through repetition.

Bit of a sidenote I worked for a German Engineering company back about 20 years ago and it was a real eye-opener for me, they are just leaps and bounds better than others in many of their methodologies and manufacturing practices. Having said that, and believe me I did not come here to :stirpot: , it is clear in real World results time and time again that their logic on relying on a 100% perfect amount of Thinset under the membrane for it to be waterproof is heavily flawed, and I think we can all agree, it really does need to be perfect to hope to achieve some level of actual water-proofing in a submerged environment (which of course any non-failed regular shower, won't be, a key point to be sure, but what happens when a slow leak failure through grout/silicone starts or in the case of a steam room it is more or less a submerged application). In even just thinking about it, it makes no sense relying on a granular porous non-waterproof adhesion material to stick 2 membrane edges together, especially when said material is not only sitting under the membrane but also extends out into exposed areas to where water is surely going to get into which then almost certainly will induce the channeling under the membrane which is what we are seeing. This is why I'm sure a company like Wedi doesn't (one reason I strongly considered them but then discounted them for other reasons) and uses their Sealant 620 instead, a polymer waterproof sealer for the edges and overlaps.

The cardboard "ice box" and tower seem like shear near miracles really, and I know Dave Gobis was the keeper and filler of the esteemed box for many years, but I really wonder if any non-Kerdi employees really seen them make it.... :foilhat:


So that brings us back to my steam room dilemma, a somewhat submerged application, and why I am not comfortable hoping that my contractor will somehow achieve the 100% perfect install required with either a Laticrete or Kerdi membrane on the floor, and then even if they do there won't be any channeling/capillary action through the porous granular thinset between the membrane edges and overlaps.

Moreover and also as I noted, their technique of installing Kerdi is to put Aqua Defense over all the seams and overlaps, this is how he says they have always done them. He is willing to do Laticrete as I noted, but I don't think he has ever used it before so I think both parties have a little less confidence going that route. I called Mapei to see what they would say about this, and at first they bucked and said no don't do that, but he assumed incorrectly that the AD was going to go over the whole sheet membrane which I then corrected. Then he said sure you can go over the exposed Thinset spots and overlap on to the membrane a little, and even agreed on why it was a good idea. I did not ask about warranty, or call Kerdi on their thoughts... lol. I think we know what those answers would have been.

I have to try and make a fast decision on this now, with the state of supply chains currently my time to decide on this is pretty much up. I do wonder how adhesion would compare in both cases, Hydroban liquid to their own sheet membrane or AD to the Kerdi membrane. I guess I should have realized no prominent installers here are likely going to come out and admit they are doing this for fear of being panned in the forum and should have also mentioned people could send me PM's LOL. :bonk:

jadnashua 04-24-2021 08:17 PM

In Europe, even with the EU as a top level organization, Schluter would have had to get approval from each country to get their preferred method approved. They decided that it just wasn't worth the effort, so they use a different mortar to make their seams that is more impervious (similar to Ardex 8+9). In the USA, they only had to gain approval with one agency, and went with what they knew would work.

Any system requires you to follow instructions. A properly done Kerdi seam can tend to wick about 1/4" or so during a water flood test, but since they require at least a 2" overlap, and a flood test is the worst situation a shower should ever see, that is usually more than enough.

In a steam shower, they have two situations: residential and commercial. The regular Kerdi won't meet the commercial requirements, but Kerdi DS does.

Anyway, use what you prefer, and follow instructions, and it's unlikely you'll have any issues long-term. While I don't have any personal experience with Schluter and exercising their warranty, I've heard that they are more lenient than many people expect with help, materials, and guidance...they have a vested interest in things working well. Note, they require buying materials from proper vendors to achieve the warranty, and not everyone that sells it qualifies. The Schluter projects I have done, have lasted without issues. Not being a pro, that's not very many...

While I think Wedi is neat stuff, their proprietary seam sealant is not cheap and smaller tile on a floor require (or at least did) the use of an epoxy thinset, which adds more to the costs.

Noble's original sheet is neat, but requires a proprietary sealant, too, and because it is so thick, seam buildup is much harder to manage. I do not know how well a liquid membrane actually works or seals into/on the fleece of something like Kerdi. While not an approved method, you could use KerdiFix on the seams, but it adds a lot of cost to the installation...about the same as making seams on Noble's product and Wedi's, too. Personally, I'm not a belt and suspender kind of guy, but if it floats your boat...you probably wouldn't get Schluter general approval, but they may not object. You'd have to call them.

jayjonbeach 05-05-2021 11:45 AM

Schluter Thin Sets have NO warranty in Steam Room!
So this is pretty crazy. In their handbook, say for continuous use steam rooms they recommend the Kerdi DS of course, and then unmodified thin set according to ANSI 118.1 standards, even though it seems the conventional wisdom would be to use modified, so in this case their All-Set.

So on the data sheets for both their "Set" and their All-Set", in the warranty section it states, "This Limited Warranty excludes exterior, submerged and steam room applications"

All these can be accessed on their website, talk about contradictions and Loop holes. A Technical Rep is supposed to get back to me on this, not feeling especially warm or fuzzy here

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