which waterproofing system for new shower?

[mtcummins]

Kerdi is a recommended method of waterproofing.

Drywall is not permitted in wet zones. You might apply Kerdi over the backsplash near your sink or behind your stove but not in your shower.

In Europe Kerdi DS is used for primary wet zones (showers) and steam applications. Kerdi is used elsewhere.

Many liquid membranes also list drywall as an acceptable substrate but you would be equally outside of industry standards if used in a shower.

Best thing to do is to phone the TTMAC or purchase their specification guide. Drywall is listed only in non-wet zones.

This is really just common sense and Jim you site the proper rules when you choose. I would imagine you have a specification guide handy. Why not open it up?

JW

Question... why would it matter? Lets for a minute leave Kerdi and all of its "problems" out of the picture. And lets have an answer that isn't just about "approved uses," but an actual rational thinking answer.

If your showers are so perfectly waterproof, who gives a crap if there's drywall behind it? It's only function is to provide a stable surface to attach the waterproofing to. Drywall is an acceptable substrate for backsplashes and other tile applications, so reason would state that it would be a sufficient substrate for a shower, if it was water tight. I thought your waterproofing was perfect, so the drywall behind a waterproof shower would actually be the best place to install it, as everywhere else, its exposed to a higher level of moisture and has a higher chance of becoming a mold problem.

That said, I'm not advocating it as a substrate behind anything that it is not specified as acceptable by the manufacturer. Kerdi specifies it as an acceptable backing. It is not acceptable to use as a tile backer w/o waterproofing in a shower, which would be a "wet zone"... can't tell you how many times I've seen that... "Ceramic tile is waterproof, right?"

[jadnashua]

Re things like glass tile. The Kerdi instructions say to call the tile manufacturer AND Schluter to come up with a suitable workaround, if it is possible. Since the requirements can be quite stringent, and you want a warranty from both the tile and the membrane user, that collaberation is required. Chances are, you can get a suitable, warranteed install, but you need to ask. Since the exact solution may vary, they require the collaberation consulation before approval. Just like you may need approval from your local building inspector if you want to do something outside the norm. If that's too much trouble, use a different product.

[johnfrwhipple]

... If your showers are so perfectly waterproof, who gives a crap if there's drywall behind it?...

Who cares if dry wall is behind the waterproofing in a shower? In a steam Room. In a commercial kitchen. A livestock plant. Outdoor BBQ. Any where that would be considered a wetzone Dry Wall is not permitted.

I care because so many shower's fail. Many kids and old timers working in large box stores are under the impression Green Dry Wall is waterproof and Mastic is the proper setting material. Scary how wrong that is.

TTMAC cares because they study failure after failure and develop National Tiling Standards that promote proper builds.

The NTCA care and does recommend dry wall either.

The ANSI Specification guide also cares and like the TTMAC also develop new standards.

It might surprise you that some of Schluter's top men are on these chairs. For example Dale Kempster is Schluter's top tech. Why not shoot him an email and see if Kerdi is OK over dry wall in your shower. Dale Kempster <dkempster@schluter.com>

Drywall has a paper backing and this backing is perfect for mold growth since it get's a food source. Condensation behind walls can cause drywall to fail and then stress the wall assembly more. Cold water lines not wrapped on warm days can drip. Also drywall is not that strong. Setting tile often involves beating the tile with a rubber mallet or pulling a tile off to check mortar coverage rates.

I would bet the men and women that make up these industry standards could add point after point to my list.

So why in the world would anyone use drywall in their shower? They might if they read that it is OK on the Kerdi instructions. And it is, around your kitchen backsplash and stove. Maybe along your laundryroom backsplash as well.

JW

If you read this Document from Gypsum Nexus (The Gypsum Association) you will get a better understanding all the new code changes envolving drywall use in bathrooms. At the bottom of the first page on the right it makes mention that Green Board (water resistant) drywall is permitted in a bathroom renovation but not in the "Wet Zone".

[johnfrwhipple]

The reason WHY drywall is allowed, is it is NOT in a wet area when Kerdi is properly installed. There should be no vapor or liquid water that gets to the drywall from the wet area, therefore not a wet area.

From the Kerdi shower installation manual, it says solid backing materials for installing Kerdi, then, the section that describes what those suitable materials are (sorry, it didn't copy/paste with all the formatting, but it's all there):
Solid Backing Materials

Gypsum wallboard – ASTM C1396/C1396M

Cementitious backer unit – ANSI A118.9 or ASTM C1325

Fiber-cement underlayment – ASTM C1288

Fiber-reinforced water-resistant gypsum backerboard/underlayment –

ASTM C1278

Coated glass mat water-resistant gypsum backerboard – ASTM C1178

Portland cement mortar – ANSI A108.1B

Concrete

Masonry

So, pick one that makes you and your local inspector happy, but ANY of these are approved.

Jim you are so wrong.

Nice try but nope. A shower is a wetzone. The application of Kerdi does not make it a dryzone. Sorry.

OMG have you no shame.

Page 33 of the TTMAC Specification guide outlines the use of drywall "Tile Installed over Gypsum Board - Thin-set Method" Dry Area's Only
The full page goes on to state "This system not to be used in wet or exterior areas such as showers, bath surrounds, steam rooms or exterior installations".

This is a huge online debate and there is much online confusion over the subject. Thanks in part to men like Jim here posting manufacture guidelines and not industry standards. Before anyone goes ahead check with the top tech at Schluter email Dale Kempster. Dale is Schluter's top tech and ask him directly. Ask for an email for your inspector because when they ask you to rip it out you will want to scream at someone.

Dale Kempster <dkempster@schluter.com> Dale by the way is on the board or chair at TTMAC.

Page 73 of the TTMAC specification guide shows "319SR-2009/2010 DETAIL B-THIN SET ON BACKER UNIT/BOARD"

Materials

- Cementitious backer unit (ANSI A118.9-1999 (2008))
- 11 mm (0.43") thick fibre-cement backer board meeting (ASTM C1288-1999)
- Coated Glass Mat Backer Board (ASTM C1178/C1178M-08) minimum 13 mm (0.51")thick


Take a look at page 21 and page 22 like the TTMAC the ANSI makes it very clear that a shower is a wet zone. If you give it a good read you will also find countless examples of "Follow all manufactures installation guidelines" "Installation procedures vary greatly" and on and on.

Because of Jim and all his repetitive selling and posting of this point I even mocked up a Kerdi sample over drywall to show my North Vancouver Inspectors. You know what they said. No. No. No.

No to Kerdi over drywall
No to Kerdi over moisture resistant drywall
and
No to Kerdi over Fire Board Drywall.

To be fair I also showed my inspector Drywall with Red Guard - he said no.
I showed him drywall with Hydro Ban - aaahhh No.


If you read this Document from Gypsum Nexus (The Gypsum Association) you will get a better understanding all the new code changes envolving drywall use in bathrooms. At the bottom of the first page on the right it makes mention that Green Board (water resistant) drywall is permitted in a bathroom renovation but not in the "Wet Zone".

[mtcummins]

I love how much confidence you have in your perfect waterproofing. Properly waterproofed drywall behind a shower wall will NEVER grow mold. The MR gyp board that you put next to the shower is 10 times as likely to mold. Simple as that.

Don't install waterproofing on drywall that the manufacturer doesn't allow.

Your code reference is for Tile on Gyp board, thinset method. Not tile on gyp board, waterproofing then thinset method. Clearly its a dumb-ass idea to put up drywall and then tile in a shower. I tear those out from time to time, especially in tub surrounds. That is a different installation.

Turns out OSB is not an acceptable roofing surface, unless you put a proper waterproof roof over top of it. Hmm... odd how that works, eh?

If you don't want to use it, put in CMU, form a mold and pour a monolithic slab of concrete and use a pool liner before waterproofing, whatever makes you happy. Kerdi over drywall is accepted in the US, maybe Canada is different.

[johnfrwhipple]

Drywall in a shower with or without Kerdi or any waterproofing product is not accepted in the US if your following NTCA and ANSI Specifications. Because you choose to use it does not make it acceptable.

Because Schluter says it's OK does not make it acceptable.

Look it up. Check with either the NTCA, ANSI or TTMAC specification guides. If your a professional installer you should understand these guidelines. As a homeowner you should know that most builders and tile men will cut corners where they can. Often the inspectors are not in to see these steps. Self inspection and specifying your crew follow these guidelines will save you from tile men and builders trying to cut corners or who have no clue what the industry standards are.

Understanding the industry standards for tile layout, lippage and such will most likely net you a better shower.

In Pittsburg just like Vancouver Kerdi over drywall is not an accepted shower backer board. Look it up. MTCummins why not call your building inspector and ask them yourself. These crazy claims by those outside of any organization is one of the prime reasons so many showers are build not to code in North America.

JW

[johnfrwhipple]

Drywall in a shower with or without Kerdi or any waterproofing product is not accepted in the US if your following NTCA and ANSI Specifications. Because you choose to use it does not make it acceptable.

Because Schluter says it's OK does not make it acceptable.

Look it up. Check with either the NTCA, ANSI or TTMAC specification guides. If your a professional installer you should understand these guidelines. As a homeowner you should know that most builders and tile men will cut corners where they can. Often the inspectors are not in to see these steps. Self inspection and specifying your crew follow these guidelines will save you from tile men and builders trying to cut corners or who have no clue what the industry standards are.

Understanding the industry standards for tile layout, lippage and such will most likely net you a better shower.

In Pittsburg just like Vancouver Kerdi over drywall is not an accepted shower backer board. Look it up. MTCummins why not call your building inspector and ask them yourself. These crazy claims by those outside of any organization is one of the prime reasons so many showers are build not to code in North America.



If you read this Document from Gypsum Nexus (The Gypsum Association) you will get a better understanding all the new code changes envolving drywall use in bathrooms. At the bottom of the first page on the right it makes mention that Green Board (water resistant) drywall is permitted in a bathroom renovation but not in the "Wet Zone".

JW

[mtcummins]

You've sited many places that very obviously state not to use gyp board as a tile backer in a shower. Good for you. You've not cited anything about the substrate of a completely waterproofed area. There is a difference.

Show me code that says you can't put kerdi on drywall.

More than that, tell me WHY a perfectly waterproof system is ever going to mold the drywall behind it. It won't happen, unless you have a leak in the wall, in which case you're pretty much screwed either way. The walls surrounding a shower or tub are far more susceptible to water damage/mold. You don't seem to have any actual answer, just some vague references to code that does not specifically state what you are claiming.

[jadnashua]

Refer to TCNA installation instruction B421.07, ANSI 118.10, and IPC as described in the test report linked http://www.johnbridge.com/images/mik...20ESR-2467.pdf

Additionally, Kerdi, installed per the manufacturer's instructions, is approved by state building codes notorious for their unique take on things in Massachusetts, Michigan, and Kentucky for places that may not adhere to the IPC, when building a shower. The TCNA 421.07 allows drywall (gypsum board).

Now, if your local codes modify these, then you must adhere to those. Just like Canada allows 1.5" drains for showers and the USA requires 2", each jurisdiction can dictate what you should use, but the test results show that, properly applied over a backing material, Kerdi is waterproof and is a decent vapor barrier. If you were in a commercial situation and required greater vapor retardation than the 0.75perm rating on Kerdi, then you'd want to install it over something else, but this is more than sufficient for any typical home use and many light commercial uses. Since it is waterPROOF, the backer material is not wet.

[mcu]

If you're using the Schluter products (Kerdi), you could get a 48x48 Schluter shower pan and cut it down to size. They're made to be cutable, so you'd just take 6" off 2 edges to get your 3x4 pan. This would save you the hassle/dry time of doing a mud bed.

There may be other cut-able pans on the market, I'm not familiar with them if there are. These Schluter pans require Kerdi over them and a Kerdi Drain to make a water-tight system. Maybe you can use other products with their pan, but I don't know about that, I just use the complete Schluter system, as it was designed to be used all together.

If you're going that route, you might as well just buy the whole shower kit and get everything in one shot. These generally run about $600.

Lemme save JW the hassle, and tell you right now that he thinks they're junk, they're overpriced, they're marketing hype, that Jim and I are getting paid by Schluter to hock their junk, etc. Its all bullshit, but that's what you're about to hear.

Choose the product you like (all of the ones JW likes are good products as well, if installed correctly), and install it properly, and you'll be fine.

mtcummunins, do you use thinset alone to do the kerdi membrane and base or also chaulking that JW is talking about? Do you use preformed shower curbs and benches or build your own?

[jadnashua]

If you want a hanging bench, either corner or along a wall, I like the Innovis Better Bench. If you're going to build a Kerdi shower, you could use either Kerdiboard to form it, a monument bench, or something like the BetterBench. There are other companies that make similar products. Using Kerdiboard means the whole bench is waterproof. A monument bench is built inside the waterproofing. The Better Bench is installed after the waterproofing, and can be installed either before or after the tile is installed. Or, you can build the bench out of wood, cover it with ply, then either drywall or backer board, then cover the whole thing with Kerdi while doing the rest of the shower.

[mtcummins]

mtcummunins, do you use thinset alone to do the kerdi membrane and base or also chaulking that JW is talking about? Do you use preformed shower curbs and benches or build your own?

I'm not sure what you mean by "thinset alone," but i like the schluter base, thinsetted down to the subfloor, then kerdi installed over that. I haven't built any huge showers, mine have pretty much all been 30-32" wide, but what I like to do is use basic roofing principles with the kerdi... start at the bottom, run the kerdi horizontally through the corners w/o seams, and overlap the edges bottom to top. This relies very little on the thinset for waterproofing, only wicking can get water past the seam. It does make the overlap area thicker than using the kerdi band, but i prefer this system. Alternatively, you could put the sheet on the wall, band over the edge and up onto your backer board, then bring the next sheet of kerdi down to the top edge of the lower sheet (rather than putting the band on top of the seam, you're lapping it like a roof). This would save you some thickness.

Anyway, back to the width... one of the things that narrow showers lets you do is run the floor piece up the walls... i center the bottom sheet w/o cutting it to width, cut out the corners, and run the edge of the 39" sheet a few inches up the wall on all edges. Then I add the corners, then bring the first wall sheet all the way to the bottom of the wall. You have to get those corners in tight (squeeze out a bit more thinset than normal), or the buildup can be too much. Again, this is roofing style... don't count on the thinset seams much, but rather the lapping of the sheet.

It is difficult to manage a sheet long enough to wrap all the way around the shower, but its worth it to me to not have seams in the inside corners.

I have used the preformed curbs mostly, but I don't think they're necessary if you do a meticulous waterproofing job. You could just as easily, and much more cheaply, build your own. But, the extra time to do that isn't really worth it to me, so I generally just get the $50 curb in the kit and use it. I've not used any of the pre-made benches. I've always had very specific requirements for them, so I like to custom build them. Same thing with niches, they really need to be custom built to be able to get exactly what you want. I'm sure some of the bench options out there are good ones, but you don't want to ask me about that, as I don't have any experience with them. For example, the shower I'm doing next is 5 feet long at the shower pan, but then steps up for the bench, and out an additional foot. This space is suspended over a staircase. Its a maximizing space move, and one that has to be custom made for the application. It's also critical that the bench then gets completely waterproofed, as its not over a pan anymore...

I like the valve seals and such they offer as well... keep it all sealed up tight.

[johnfrwhipple]

mtcummunins, do you use thinset alone to do the kerdi membrane and base or also chaulking that JW is talking about? Do you use preformed shower curbs and benches or build your own?

The chaulking is called Kerdi Fix and sells for about $26.00 per tube here in Vancouver. For seaming pieces of Kerdi together it is the only way to go, unless you can get your hands on Kerdi Coll the two part thin set they use in Germany for seaming Kerdi and Kerdi DS together.

I thought you where using the Prova Base? They might not have this chaulking.

Shower niches and benches are easy made on site or you can order ready made ones from Noble Company.

Drywall is not allowed in showers.


If you read this Document from Gypsum Nexus (The Gypsum Association) you will get a better understanding all the new code changes envolving drywall use in bathrooms. At the bottom of the first page on the right it makes mention that Green Board (water resistant) drywall is permitted in a bathroom renovation but not in the "Wet Zone".

These boys know this but have choosen to confuse the issue. Build a better shower. Do not use drywall as suggested to save money.

Consider using a thicker membrane, if you do switch from the Prova system and go the Kerdi kit remember you are getting a waterproofing system roughly 1/4 the thickness of your credit card.

[jadnashua]

Is 1/8" glass any less waterproof than 1/2" glass? Kerdi passes the ANSI 118.10 test as a waterproof membrane.

[mtcummins]

It might surprise you that some of Schluter's top men are on these chairs. For example Dale Kempster is Schluter's top tech. Why not shoot him an email and see if Kerdi is OK over dry wall in your shower. Dale Kempster <dkempster@schluter.com>

Hmm... so you mean to tell me that the top tech at Schluter, who is on a chair of one of the many organizations names that you like to throw around (without referencing anything that actually says what you're claiming), along with all the other Schluter higher ups who are on other boards, allowed the Schluter SHOWER system instructions to specifically list Drywall as one of the proper substrates (and actually the FIRST in the list of substrates), when the organizations they chair supposedly say that it is totally unallowable? Hmm, thanks for convincing me that you're full of crap once again.