Kerdi membrane install question.

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Pete C

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I am building a walk in shower. the Sheetrock is up, time to start putting up the Kerdi.

In demo video, they band all corners and lay sheets cut to each wall. Is there any reason I can't use single sheets to go around corners? I understand placing each sheet will be a bit more work, but, it would seem to me that fewer seams is better and also saves a little material. I was wondering if maybe it had to do with the thin set setting up very quickly, allowing little time to fuss with the kerdi.

Or maybe Schluter likes selling Kerdi Band!
 

Jadnashua

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It's much easier to use smaller sheets than to try to go around a corner. While Kerdi-Band is thinner and makes for a smaller buildup, you can use a band of the Kerdi material...it would depend somewhat on the tile you used whether that would be an issue. The last thing you want is to have the thinset skinning over before you get the last but up. Depending on the wall width, I've also not cut it, run the edge of the sheet around the corner instead of using the band material.
 

JohnfrWhipple

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Install Answers for Kerdi Membrane - TCNA and TTMAC do NOT allow drywall in a shower

I have deleted all my posts showcasing Kerdi, Ditra and the like from Schluter Systems. I have stopped using these products and do not recommend them now to my online clients, my local customers. You will not see photos here going forward. No one asked me to delete these photos. No one told me to delete them. I feel these products from Schluter come with far to many restrictions and that the testing of the products leaves lots to be desired.

It was my testing of the niches and resulting phone call to review my findings that finalized my decision to switch to a more premium waterproofing approach a quit using Schluter's products all together...

If you need help with a Kerdi Question email Dale at DKempster@schluter.com - this is Schluter's top tech. Remember that Jadnashua (Jim) here on Terry's forum is not in this business and by my account works to privately promote Schluter and the John Bridge Tile Forum.
 
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Pete C

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john, that was my thought as well, but the kerdi dealer says sheetrock is fine. i think it might have to do with the cement board sucking the moisture out of the thinset too quickly.
 

Jadnashua

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If you install Kerdi properly, the drywall stays as dry as it does in any room. A failure of your plumbing, while always possible, could damage it. But, a failure of your plumbing in any area of the house is problematic. Just do it right, and it should outlast the house.
 

Jadnashua

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To be fair, almost none of the 'showers' being shown in the demos are real...they're mockup walls and floors, intended to show the application of the membrane, not the structure of the house.
 

DougB

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John,

I'm remodeling a bathroom, with an drop-in tub/shower in an alcove. I'm using cement board. Is there any advantage of using the Ardex product instead of Red Guard or Hydroban?

For the rest of the bathroom, I was planning to use regular drywall, and tile over that. Is tiling over drywall OK? Should I prime the drywall first? What do you do?
 
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Amish Electrician

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Pete, I don't mean to 'pile on,' but .... NO GYPSUM in the shower! Not even the green or blue stuff!

Yea, I know, various vendors make various claims. Read the fine print. There's a lot of 'maybes' in there. Murphy's Law will ensure that something goes wrong.

I'm not a plumber; I do electric work. Several of my customers are property-management firms, so I get to see plenty of remodel work. I have yet to see a any gypsum product, any tile job, survive.

So, when I do my bath, it will be cement board 100%, even on the ceiling. If nothing else, the cement board won't dent when you hit it with a mop handle. No paper or glue to feed mold, either. Skim coat it with real plaster, and it's as waterproof as steel plate.

FWIW, my walls are getting covered with FRP (fiberglass reinforced plastic) sheeting. Absolutely waterproof, with very few seams - and none of the seams are horizontal. It's that pebbly stuff you see in commercial kitchens and public restrooms.

Maybe I'm over-doing it, but the difference in materials cost is not that much. It amazes me that folks will spend a fortune on getting just the 'right tile,' yet compromise on the basic structure.
 

Jadnashua

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Kerdi is a waterproof membrane. When it is installed properly, once you protect it with tile, no moisture penetrates it. John is a belt and suspender kind of person. Being in a business where you never want callbacks, it has some merit if people are willing to pay for it. Schluter has paid for an independent testing of Kerdi membrane installed over drywall and it passes all industry specifications for moisture protections IF IT IS INSTALLED PROPERLY. In my 60+ years, I've never had a belt or suspender fail, and have never worn both. You either believe the manufacturer and the testing, or you don't. They do not force you to use drywall, they also list other acceptable materials, which includes cbu. You use what you feel comfortable with and local regulations require. There are thousands and thousands of Kerdi showers in use today applied over drywall that are as dry as the day they were built. If you have a leak, it's either because of poor workmanship or an accidental puncture that occurred after testing and before tile. A leak would require fixing whether it was cbu behind it or drywall whether it was through the membrane or from a plumbing leak behind it. If you don't believe a single layer waterproofer is sufficient, then you'd want cbu on your walls and especially next to your windows in all the rooms of your house, or make the walls poured concrete. A house exposed to rain driver gale and hurricane force winds is a much more hostile environment than a shower. I trust my shingles and paint on the outside of the house to protect the interior walls as I do Kerdi to protect my shower. Feel free to augment it if it makes you feel better. I've got the certification test document somewhere, but you can find a copy on-line if you look. Since the test is only valid for a few years, it gets repeated, and has always passed. Most local inspectors will allow installation to the manufacturer's instructions with that certification. Some won't, and then you do what you have to should you want to use that material. There are lots of choices, pick one you're comfortable with, but installed properly per the manufacturer's instructions, they all work. Some give you more margin for error than others, but if you trust your workmanship and workplace environment to not compromise it, that's somewhat irrelevant. FWIW, in the USA (don't know what the duty is to Canada), you can pick up Kerdi membrane for around $1.75/sq ft fairly easily. Many places offer free ground shipping. Also, if you believe the websites selling it, list price is in the order of $1.91/sqft. Canada can have some high tariffs on things, so your pricing could vary considerably as well as shipping.
 
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Amish Electrician

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OK, Jad, I won't debate your religion with you.

"IF" is the biggest word in the language. Heck, I'd win the lotto IF I pick the right numbers. IF the Queen had balls, she'd be King.

BTDT.

So go ahead, get by with the minimum possible. I'm confident you also wear Wal-Mart $8 sneakers and drive a Yugo ... after all, they meet all the same regulations as the expensive name brands, so they must be just as good.

While you're fumbling through all that documentation ... I seem to recall seeing somewhere that there were model codes that banned drywall and greenboard from 'wet' areas, like showers- no matter what was over them. You might want to be sure ... and get the permit and inspection as well.

Everything I need to fix in my house is the direct result of someone being 'smarter' than the rule book.
 

DougB

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OK, Jad, I won't debate your religion with you.

Everything I need to fix in my house is the direct result of someone being 'smarter' than the rule book.

Hey, what's wrong with a safety factor of .9?? :)

Here in Minneapolis we had a 1965 POS bridge (I 35-W) over the Mississippi. It was a bare bones design, a nightmare. Every year the state had it inspected cause it kept rusting - until it collapsed (5-6 yrs ago) with about 40 cars on it. Killed some people, maimed others. But it passed inspection. Cost the state some nice $change$.
 
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Jadnashua

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I would ask you: How many Kerdi showers have you installed?
Personally, I've installed several, seen many more installed, and in contact with people that have installed many hundreds. Some argue that paid testing is biased. But, if you believe that , then you'd ignore any UL, CSA, IAMPCO, or other testing that is paid for by the manufacturer. I don't put storm windows over my windows, or an awning over my roof, to give things a second waterproofing layer...I believe, that properly installed, they can do their designed job, as I do believe Kerdi works as designed. I don't care what you use, if it is not installed properly, you can have problems. I happen to drive a BMW, but that should be irrelevant to the issue. I'm not adverse to spending more for better things, but at some point, more doesn't buy you anything except a smaller bank account, personal preferences aside.
 

Pete C

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Wow, looks like my thread came back to life in a big way this past week. Here is where I stand.

My shower is drywalled, ready for the kerdi. Haven't hung a single piece yet. Have an expensive roll of it sitting here waiting. I bought the entire roll with the understanding that I can return any I don't use.

My gut feeling, even as I was hanging the drywall was that it was a bad idea, but the kerdi dealer was adamant that drywall is the way to go. I now realize that maybe this is a marketing strategy. Kind of their way of saying their product is infalible.

So, do I rip out 50 bucks worth of drywall to avoid later ripping out a thousand bucks worth of tile/kerdi or do I continue taking great care to do it right? I am kind of leaning towards moving on and just making sure I do it right. And crossing my fingers!!!!

So, did I read right that a coat of drywall primer would be a good idea? BTW, the mortar I have is Versabond fortified thinset. I bought it from Ace hardware.

Recommendations on primer or anything else are greatly appreciated. Thanks for all your help.

Pete
 

Jadnashua

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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.
 

muskymike

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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.
 

muskymike

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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.
 

Jadnashua

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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.
 

Pete C

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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?
 
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