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Old 11-07-2011, 06:11 PM   #16
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Type of material to use in tub area


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Originally Posted by jeffnc View Post
. You can use drywall or plywood or whatever you want that's sturdy enough to hold tile.

Welcome New Guy---As pros we try to give advice that is 'best practice'

And 'code'

We back up our advice with years of experience along with education like the teachings of the Tile Council of America..

You suggestions of drywall violate code in the United States---
And the suggestion of plywood goes against the accepted practices and the research done by the TCNA.

So please learn before you teach---Mike---

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Old 11-07-2011, 06:23 PM   #17
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Type of material to use in tub area


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Welcome New Guy---As pros we try to give advice that is 'best practice'

And 'code'

We back up our advice with years of experience along with education like the teachings of the Tile Council of America..

You suggestions of drywall violate code in the United States---
And the suggestion of plywood goes against the accepted practices and the research done by the TCNA.

So please learn before you teach---Mike---
Get up to speed Mike and try to pay attention to context. I have no doubt you're going on years of experience, but you need to keep up to date with modern techniques.

I was just at the TCNA in Clemson not long ago, so this is straight from the horse's mouth.

Kerdi over drywall is to code and accepted by TCNA and recommended by the manufacturer (manufacturer directions trump code in most cases anyway).
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Old 11-07-2011, 06:32 PM   #18
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Type of material to use in tub area


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And the suggestion of plywood goes against the accepted practices and the research done by the TCNA.
I stick with drywall, but I do take back putting Kerdi over plywood. I was thinking of Ditra when I wrote that, and just typed too quickly. Plywood is not dimensionally stable like cement board or drywall. This is fine under Ditra since the Ditra corrects for that - Kerdi can't.

Again, it makes more sense to put tile over Kerdi over drywall than over cement board. Completely code approved, TCNA accepted and manufacturer recommended.

Putting the waterproofing barrier behind cement board, as the poster wrote that I was responding to, makes no sense.
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Old 11-07-2011, 06:38 PM   #19
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Type of material to use in tub area


I will admit that Schluter and the TCNA accept that Kerdi over drywall is accepted by both.

That still doesn't change my statement--The use of drywall and green board is still against code in the U.S.

By the way,I was paying attention and I'm to old to get up to speed.

Your advice will cause a failure on an inspected job in the U.S. until the day the code is changed.
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Old 11-07-2011, 07:07 PM   #20
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Type of material to use in tub area


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I will admit that Schluter and the TCNA accept that Kerdi over drywall is accepted by both.

That still doesn't change my statement--The use of drywall and green board is still against code in the U.S.

By the way,I was paying attention and I'm to old to get up to speed.

Your advice will cause a failure on an inspected job in the U.S. until the day the code is changed.
No, it's not against code.

Keep 2 things in mind.

1) Manufacturer's instructions trump codes in most cases, and this is no exception.

2) Technically, it does not violate the code as written even without taking into consideration manufacturer's instructions. Drywall is not allowed in wet areas. The area behind a Kerdi membrane is not a wet area any more than the outside of a copper pipe is a wet area or the outside of a Romex cable is an electrically energized area.

An inspector might fail a Kerdi installation over drywall, but an inspector might fail any other number of things that are correct and best practices as well. This does not mean it's not to code, it just means the inspector is wrong. And you are definitely wrong that it will not pass the inspection, because it obviously has passed many times. Maybe in your experience it has failed, which is beside the point of whether it's a best practice or allowed by code.

See also this thread.
http://www.johnbridge.com/vbulletin/...ad.php?t=47133
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Old 11-07-2011, 07:09 PM   #21
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Type of material to use in tub area


Both the membrane over drywall and cement board method are pretty bombproof, IMO.

Putting cement board over a barrier is proven and works, i've taken apart a few rotten bathrooms and never seen a scenario where rot was found behind cement board.

so hey what do you guys think about denshield backer board?, manufacturer installation says it doesn't require an additional barrier behind.

Last edited by chrisBC; 11-07-2011 at 07:18 PM.
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Old 11-07-2011, 08:08 PM   #22
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Type of material to use in tub area


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Then in #16 you mistakenly said it's OK to Kerdi over plywood.
I was thinking of Ditra when I said that and have already corrected. Did you miss it or intentionally ignore it?

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You then criticized Mike for saying that wallboard is not allowed in wet areas in the USA. (He is right) You responded by adding Kerdi over wallboard was OK.
No, we've been talking about Kerdi all along. I responded to a poster who talked about putting it behind cement board. I said it belongs in front, and once you do that you can even use drywall. Mike started arguing with that.
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Old 11-07-2011, 09:31 PM   #23
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Type of material to use in tub area


Quote:
I was thinking of Ditra when I said that and have already corrected. Did you miss it or intentionally ignore it?
I didn't miss anything. Everyone knows you corrected yourself later. Seems to me it would be second nature for a tile setter to know plywood in wet areas is not a recommend method. It is to me at least.

When you tell us we can use regular plain drywall in a shower IF it's covered by Kerdi, you are not telling us anything we didn't know 15 years ago or longer. But thanks anyway since ur new.

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Old 11-07-2011, 09:36 PM   #24
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Type of material to use in tub area


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I didn't miss anything. Everyone knows you corrected yourself later. Seems to me it would be second nature for a tile setter to know plywood in wet areas is not a recommend method. It is to me at least.
Me too. Have you ever misspoke?

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When you tell us we can use regular plain drywall in a shower IF it's covered by Kerdi, you are not telling us anything we didn't know 15 years ago or longer.
Really? Us? So you're speaking for your whole "team" here then? So then maybe you can tell me why there's an argument about it.
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Old 11-07-2011, 09:43 PM   #25
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We aren't a team--Jaz and Bud set me straight on a regular basis---We all 'misspeak' now and again.

And I thank them both when they do.

The bottom line for me is getting good sound advice to a member----If I'm wrong I want to know.--Mike---
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Old 11-07-2011, 09:45 PM   #26
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wow, this is getting boring fast, someones a little argumentative

anyways, i'm curious what ended up happening with the OP and the contractor putting up greenboard.
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Old 11-07-2011, 10:01 PM   #27
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Type of material to use in tub area


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Putting cement board over a barrier is proven and works.
I'm not really convinced. You've got a situation where a porous, wicking type of material is attached to a membrane with screw holes piercing it. Seems to me this is pretty similar to leaving exposed nails on a shingled roof. Different, but similar.
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Old 11-07-2011, 10:09 PM   #28
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I'm not really convinced. You've got a situation where a porous, wicking type of material is attached to a membrane with screw holes piercing it. Seems to me this is pretty similar to leaving exposed nails on a shingled roof. Different, but similar.
I see your point, however I'm not sure it will lead to anything major. What happens if the membrane over the drywall develops a leak? As I was saying, i've taken apart rotten bathrooms, and I have yet to take one apart that was done with cement board. If I come across a bathroom where the framing is completely rotten, and the cement board was installed properly with a barrier, then I might change my mind. I guess time will tell. At any rate, I think either method is highly superior to drywall/greenboard with tiles set right on top.

I'm still curious what everyone thinks about denshield backer board. The manufacturer claims that the waterproof membrane is built in, no need for an additional one. Also instructs to set the screws flush, not to countersink. I'm not a bathroom specialist and don't do them too often, so just curious what the tile/bathroom people think.
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Old 11-07-2011, 10:17 PM   #29
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Type of material to use in tub area


Moisture-Wick Testing

DensShield Tile Backer and the leading brands of cement
board were subjected to wicking tests according to the
Ceramic Tile Institute test procedures CTI-T83. The tests
showed that within a 24-hour period, cement board will
wick at least 3 up the board while DensShield will wick
less than one-third of 1” (.319) during that same period.
From: http://docs.google.com/viewer?a=v&q=...WlK87HmnplLw0w

Fiberock and greenboard are not allowed per some codes: http://www.jameshardie.com/pdf/backe...rison-half.pdf

DUROCK is water durable and moisture, mold resistant: http://www.usg.com/durock-cement-board.html

“Q: What is the difference between DensGuard tile backer and cement board or fiber-cement board?

A: While cement-based backer boards are water-durable they do not contribute to proper moisture management. In order to prevent the passage of moisture into the tile assembly the Tile Council of North America requires the use of a membrane to block the passage of moisture, since both the wall cavity and the floor substrate are susceptible to moisture damage. DensGuard tile backer has a built-in moisture barrier on the face which protects the wall cavity and floor substrate. It is at least 30% lighter than leading cement-based boards and has a non-abrasive, moisture-resistant core. Cement board has a heavy, crumbly, abrasive core, which can scratch tubs and fixtures. In addition, unlike cement-based backers, DensGuard backer board does not require any special tools or fasteners to cut and install.”---- from: http://www.gp.com/build/faq.aspx#faq_10360

Ciperez, are you installing tile directly on the greenboard?

Gary
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Old 11-07-2011, 10:44 PM   #30
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What happens if the membrane over the drywall develops a leak?
Well, I've personally never seen a failure behind a Kerdi system. But then again, they're not used much in the grand scheme of things, and are relatively new to this country. But in talking to the guys at TCNA and Schluter reps, this is supposedly a problem.

I was told that if the membrane is pierced for any reason, either the Kerdi must be patched, or the hole must be waterproofed. For example if you screw your glass shower door into your shower curb through the Kerdi, you have to fill the hole with KerdiFix or equivalent before driving the screw.

They described a tile guy who used to use nails (actual 16d nails driven into the backer board substrate) to space his tiles. He wasn't familiar with Kerdi the first time he was hired to tile over it, and put his nails there too. This was described to me as a laughable disaster requiring all the Kerdi to be reinstalled. Those holes were on vertical surfaces and would be filled with thinset. Worse than screw holes through plastic I suppose, but still....

Maybe they're being overly cautious. This is not just Schluter reps covering their asses for warranty purposes though.

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