Kerdi Question

[Kestrel]

Hello gang - many thanks again for the help on this blog.
Basement remodel almost done - nearing drywall. I'm planning on using a Kerdi drain, floor, curb and membrane for the walk-in shower stall, with tile over. Now their literature says to use regular drywall, but all of the installers (2 so far) I've had look at the job think it's nuts and propose some other, I think fiberglass stuff, with ceramic screws.

I guess I'm looking for some experience-based opinions that the Kerdi membrane and system are reliable, and that going with their (Schleurter's) specs - despite the drywallers' reticence - is OK.

[jadnashua]

Drywall is an industry approved method according the the TCNA when used underneath Kerdi. You do NOT want them to mud and tape the seams where you are going to install the membrane, the thinset and membrane will provide that function. When installed properly no moisture from the shower will get beneath the membrane and the drywall stays dry, retaining all strength it had upon installation.

Installing cbu, and I'd guess (haven't looked recently) the fiberglass faced backer boards, are also one of the listed approved backers. Because you have a lot of area to spread the thinset on, if you use cbu, you want to wipe it down with a wet sponge to do two things: remove any dust and to provide some moisture so it doesn't suck it all from the thinset, making it dry, which is then hard to embed the membrane's fleece into properly.

Schluter has decades of history of using drywall, but they also list other materials that are suitable...go with the one you prefer, but in any case, done right, none of them are a problem waiting to happen. If you had a leak from say the plumbing, cbu would likely survive, drywall might not depending on how bad and how long it went before discovery, so that is a strike against that...but, consider all other areas in the house where there's drywall and plumbing behind it...do you worry about that, too? Plumbing does not magically leak. Obviously, it can, but it's not all that common unless disturbed or incorrectly installed (same with the membrane). Do it right, do it once, and don't worry.

[johnfrwhipple]

Oh man.

Hear we go again.

Drywall is not approved in any shower - covered with Kerdi or not. Use cement board, Hardi board or Green EBoard (not green drywall). Anyone telling you that it's OK to use drywalll in the shower is in the business of selling Kerdi, not building showers.

The TCNA also recommends drywall only in dry areas. No where does it state Kerdi can be used in a shower with drywall.

The drywall industry does not promote it.

Mapei does not promote it.

Custom Building Products do not promote it.

Laticrete does not promote it.

If you really want to use drywall and really believe it's OK call Schluter and ask which thin-set to use. Ask them which primer to use. When they talk in circles and say things like we don't recommend one specific brand then call Custom Building Products, Mapei or Laticrete and ask them. They will tell you drywall is a mistake in the shower and outside industry guidelines.

Only Schluter will do this.

Now you have the business of only a five year warranty. If you must use Kerdi - use Ardex setting materials. This will double your warranty to ten years.

Now if you want a 15 year warranty you can build your shower with Mapei's products - I love them and use them all the time.

Or you can use Laticrete or Custom Building Products and get a 25 year warranty.

In all these extended install warranties one thing is common - there is no drywall in the assembly.

It was recommended to me that if drywall where to be used in a shower that a Schluter rep should inspect and document to job. What a pain. Just use a proper backer board.

Drywall is ____ and has no business in your shower renovation's wet zone.

Once built make sure your tile crew flood tests it. Have your requested this?

Also tell your crew you expect all TCNA specifications to be followed for this build. Good luck.

JW

[jadnashua]

The TCNA NEVER calls out brand names, but under Shower Receptors method B422-11, which appears to be the same as B422-09,
which appears to be the same as B422-07 depending on the year of the manual you have, it discusses membranes and specifically DOES list drywall as one of the allowable materials. Now, SOME places prohibit it, and if you live there, you abide by your local requirements or your preferences. It is not REQUIRED to use drywall, and they list other materials that will also work. They list in the requirements section that the solid backer must comply with either: W201, W241, W243, W244C, or W244F where W243 (INterior walls, wood or metal studs, gypsum board with dry-set or latex-portland cement mortar) is the gypsum board as a solid backer material. These requirements have not changed for ages, and saying it is not an approved method (for most places, anyway), is just plain wrong! If the document wasn't copyrighted, I'd post a scan of the appropriate pages, but you can look it up yourself. There's another provision in there: installed per the manufacturer's instructions, and yes, in the Schluter documentation, drywall IS listed as one of the approved backer materials.

That method is called Solid Backing Bonded Waterproof Membrane Integrated Bonding Flange Ceramic Tile.

Whether you like it or not, it is an approved method for most people's use. Should you prefer to use something more robust in case of potential system failures (don't happen if you follow instructions and have good workmanship), then I don't have any problem with that - go for it.

[johnfrwhipple]

The TCNA NEVER calls out brand names, but under Shower Receptors method B422-11, which appears to be the same as B422-09,
which appears to be the same as B422-07 depending on the year of the manual you have, it discusses membranes and specifically DOES list drywall as one of the allowable materials. Now, SOME places prohibit it, and if you live there, you abide by your local requirements or your preferences. It is not REQUIRED to use drywall, and they list other materials that will also work. They list in the requirements section that the solid backer must comply with either: W201, W241, W243, W244C, or W244F where W243 (INterior walls, wood or metal studs, gypsum board with dry-set or latex-portland cement mortar) is the gypsum board as a solid backer material. These requirements have not changed for ages, and saying it is not an approved method (for most places, anyway), is just plain wrong! If the document wasn't copyrighted, I'd post a scan of the appropriate pages, but you can look it up yourself. There's another provision in there: installed per the manufacturer's instructions, and yes, in the Schluter documentation, drywall IS listed as one of the approved backer materials.

That method is called Solid Backing Bonded Waterproof Membrane Integrated Bonding Flange Ceramic Tile.

Whether you like it or not, it is an approved method for most people's use. Should you prefer to use something more robust in case of potential system failures (don't happen if you follow instructions and have good workmanship), then I don't have any problem with that - go for it.

You need a new book Jim.

The acceptable backer boards for the last shower receptor do not include drywall.

You can use Kerdi over drywall in the kitchen - just not the shower.

Jim you can not mix up the methods and call it a day. You need to pick a system and follow it.

Dry Wall is not permitted in showers

[jadnashua]

Okay, it took me awhile to get this, but by permission, I'm quoting an e-mail I got from the TCNA rep. Basically, they no longer recommend gypsum board underneath a waterproof membrane in a shower construction because not ALL membrane or board manufactuers do. But, they DO allow it IF both the backer board and membrane manufacturers are in agreement. In the case of Schluter and Kerdi, Schluter has paid an independent testing agency to verify their claims that it works, and done properly, they will warranty the work. Since the TCNA has no general agreement from manufactuers of other products with the same general characteristics, they do not make a generic recommendation, but reference it to basically, follow the manufacturers instructions. Now, anything can fail if you don't have good workmanship. Here's the quoted e-mail info:

"Hello Jim,

While some membrane manufacturers promote use of their
membrane in a B422 installation with gypsum board (W243) as the solid backing,
other membrane manufacturers do not. At the same time, not all manufacturers of
gypsum board recommend their product be used in a B422 installation. Thus, the
Handbook leaves the determination of a suitable membrane/backer board
combination up to the membrane and backer board manufacturers to declare and up
to the design professional to select/specify. Ideally, one should find
recommendations from both materials manufacturers that agree. However, as you
are aware, manufacturers do put forth proprietary recommendations, which the
Handbook does not address, such as in the case you are asking about.


Many in the industry feel that building code prohibits the use of gypsum
board in wet areas, even when a waterproof membrane is applied to the surface.
However this is a matter of code interpretation, with the actual code language
somewhat ambiguous, and with some feeling the code only prohibits direct bond of
tile to gypsum board in wet areas.

At the Handbook meeting last month,
the Handbook Committee voted not to include a shower method where a mortar bed
(cleavage membrane, metal lath, and wall mud) is installed over gypsum board.
This is different from the method/materials you are asking about, but I am
mentioning it to provide some perspective on recent consensus out of the
Handbook Committee regarding use of gypsum board in wet areas. Again, the
methods are different; in no way do I mean to imply the Committee feels the same
about gypsum in a shower if a waterproof membrane were applied. What I can say
is, the amount of water/steam exposure generally is raised as a factor for
determining suitability in discussions of this topic.

For further
information, you may also want to contact the Gypsum Association.

Best
regards,
Stephanie Samulski"

[johnfrwhipple]

"...At the same time, not all manufacturers of
gypsum board recommend their product be used in a B422 installation. Thus, the
Handbook leaves the determination of a suitable membrane/backer board
combination up to the membrane and backer board manufacturers to declare and up
to the design professional to select/specify...."

She left out the part about the setting material company's opinion.

So if you can find a drywall producer who allows it.

Then find a waterproofing manufacture that does (only Schluter to my knowledge)

And find a setting material supplier that thinks it's OK then you might have a leg to stand on.

And you forgot to mention you also need permission from your local building inspector. I have brought all this info down to them and here in Vancouver the answer to the question of "Can I used drywall in a shower if I cover it with Kerdi?" is NO.

No you can't.

No your not allowed to use drywall in a shower.

No. No. No.

The fact that a company selling a membrane has no say over the local building code departments.

What a crazy idea using drywall in a shower. If you want Kerdi - use Hardie backer. use Cement Board.

Place a piece of drywall in your kitchen sink for ten minuntes (full of water) Place a sheet of concrete board in at the same time.

Take them out.

Try and snap the cement board. Try and snap the drywall.

Why anyone promotes this is for no other reason than to sell it as a cost saving's measure. It's not better for your shower it's cheaper!

It should register with anyone researching this point that only one company says it's OK. And they don't even install it that way in the country it's made!

Think about it.

"....Many in the industry feel that building code prohibits the use of gypsum
board in wet areas, even when a waterproof membrane is applied to the surface.
However this is a matter of code interpretation, with the actual code language
somewhat ambiguous, and with some feeling the code only prohibits direct bond of
tile to gypsum board in wet areas....."

Interpepretation? The local code here outlines what boards can be used in showers. Drywall is not on the list. How do you get that wrong? Drywall is not on the list. So what is the confusion Jim? Seriously Jim do you own shares in Kerdi? I thought they where a private company.

Drywall is not allowed in shower construction - period.

JW