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Old 08-19-2008, 09:27 AM   #1
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Can I install Kerdi over primed drywall in a basement bathroom?


I am finishing my basement. In the bathroom, I have installed the drywall with green board. It is primed. Now I would like to install Kerdi over the wall for a shower enclosure. Can I install Kerdi over the primed drywall or do I need to tear down the wall and put on a new backer board? People has raised concerns about the validity of primer holding the Kerdi. Your advise will be mostly appreciated.

Mechelle

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Old 08-19-2008, 01:49 PM   #2
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Can I install Kerdi over primed drywall in a basement bathroom?


There are one or two code inspectors here who will say: no, that you can only put Kerdi or a waterproofing membrane over cement board in a wet area inside.

Schluter says you can put Kerdi over drywall - in fact encourage it. But when it comes down to it, your inspector may have the last word, if you plan on having a permit pulled. It is a matter of time before the various code inspector jurisdictions all see eye-to-eye on this, so you may not have much choice...but one day it will be allowed.

The TTMAC (Terrazzo, Tile&Marble Association Canada) guideline 305W-2006/2007 says to use cbu too. But when it comes to mentioning the waterproof membrane, it says "follow the manufacturers recommendations". So it comes down to whether or not you have an inspector there.

Personnally, I use inspectors for plumbing, electrical and structural issues. I don't for my walls...don't think I need to IMO.

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Old 08-19-2008, 06:01 PM   #3
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Can I install Kerdi over primed drywall in a basement bathroom?


Ask them directly: info@schluter.com
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Old 03-28-2012, 01:30 AM   #4
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Can I install Kerdi over primed drywall in a basement bathroom?


I did ask the question of Schluter and they only allow it over plain drywall. No primers. No tapping mud.

If it's primed it is a deal breaker unless you get a Schluter rep to sign off on it.

Drywall is not an approved backer board so if this primed board is in your shower it needs to be ripped out.

Drywall was removed from all shower use a couple years back. A lot of guys havn't quite caught up to speed.

JW
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Old 03-28-2012, 08:36 PM   #5
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Can I install Kerdi over primed drywall in a basement bathroom?


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I did ask the question of Schluter and they only allow it over plain drywall. No primers. No tapping mud.
I do not agree. I asked too and the answer is to follow the directions and recommendations of the thinset manufacturer. The drywall coated with cured primer doesn't care that Kerdi will be bonded to it. If the thinset will bond to the primer, (and I have never found one that will not), you are good. Matter of fact it is recommended that primer be used when for example the seams were mudded with joint compound before thinset mortar is used. We all know drywall mud is bad stuff under thinset or mastic.

Quote:
Drywall is not an approved backer board so if this primed board is in your shower it needs to be ripped out.
Schluter recommends regular wallboard for use under Kerdi. Matter of fact using certain other CBU's can cause installation problems because for one thing they "suck" the moisture from the adhesive.

I can make Swiss Cheese waterproof with Kerdi over it.

Jaz
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Old 04-04-2012, 01:52 PM   #6
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Can I install Kerdi over primed drywall in a basement bathroom?


Quote:
I do not agree. I asked too and the answer is to follow the directions and recommendations of the thinset manufacturer. The drywall coated with cured primer doesn't care that Kerdi will be bonded to it. If the thinset will bond to the primer, (and I have never found one that will not), you are good. Matter of fact it is recommended that primer be used when for example the seams were mudded with joint compound before thinset mortar is used. We all know drywall mud is bad stuff under thinset or mastic.
Jaz is exactly correct.

Quote:
Schluter recommends regular wallboard for use under Kerdi. Matter of fact using certain other CBU's can cause installation problems because for one thing they "suck" the moisture from the adhesive.
Again...exactly correct.
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Old 04-04-2012, 02:18 PM   #7
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Can I install Kerdi over primed drywall in a basement bathroom?


Bud,

WELCOME BACK!

Jaz
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Old 04-04-2012, 02:31 PM   #8
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Can I install Kerdi over primed drywall in a basement bathroom?


Not back just bored on a rainy day.
I was nosing around and I can see the same ole nonsense advice is still being given by the same inexperienced responders I took issue with that got me in trouble. Some things just never change.
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Old 04-04-2012, 04:18 PM   #9
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Can I install Kerdi over primed drywall in a basement bathroom?


I know what you mean, although the one "worst" offender of recent time hasn't been seen here lately. I don't know if he decided stop the nonsense or if he was asked to get some knowledge. I hate to keep on his back, but I just can't let bad advice slip by. The average non-tile expert is liable to believe whatever is written just because it is.

What we object is not that some people just don't know the right way to do things, it's that they pretend to know. Many have still not given any credentials or way to contact them, or perhaps read some articles or their thoughts of the industry.

Take is easy, hope to see you here more often in the future.

Jaz
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Old 04-14-2012, 04:58 AM   #10
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Can I install Kerdi over primed drywall in a basement bathroom?


Quote:
Originally Posted by JazMan View Post
I know what you mean, although the one "worst" offender of recent time hasn't been seen here lately. I don't know if he decided stop the nonsense or if he was asked to get some knowledge. I hate to keep on his back, but I just can't let bad advice slip by. The average non-tile expert is liable to believe whatever is written just because it is.

What we object is not that some people just don't know the right way to do things, it's that they pretend to know. Many have still not given any credentials or way to contact them, or perhaps read some articles or their thoughts of the industry.

Take is easy, hope to see you here more often in the future.

Jaz
I wouldn't worry too much. Only the 1 and done topic posters are at risk for bad advice. I frequent the forums here and have a pretty good idea of the people who know what they're talking about on any given subject. I assume that other people who spend time here, have the same list. If one of those people weigh in on the topic, I consider that the answer, regardless of what else has been posted. Not to kiss your behind, but when it comes to tiling questions, I do it the way you or Bud describe it. That way I know the only way its coming out is because I don't like how it looks anymore, not installation failure.
P.S. I like it when you guys have the time to explain the reason for doing it your way, helps with my understanding in the long run
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Old 04-14-2012, 09:52 AM   #11
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Can I install Kerdi over primed drywall in a basement bathroom?


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I wouldn't worry too much. Only the 1 and done topic posters are at risk for bad advice.
That's a good point!!! The "drive-bys" create their own perils I suppose.
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Old 04-15-2012, 10:43 AM   #12
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Can I install Kerdi over primed drywall in a basement bathroom?


Quote:
Originally Posted by Mechelle View Post
I am finishing my basement. In the bathroom, I have installed the drywall with green board. It is primed. Now I would like to install Kerdi over the wall for a shower enclosure. Can I install Kerdi over the primed drywall or do I need to tear down the wall and put on a new backer board? People has raised concerns about the validity of primer holding the Kerdi. Your advise will be mostly appreciated.

Mechelle
Mechelle make sure you only use plain drywall with your kerdi installs. No paint primer allowed. No drywall mud allowed. And this install over plain drywall is only approved in dry zones so if your drywall is in the shower it will need to be removed.

In the shower switch to cement board for your Kerdi. Or Hardi Board. Or wonder board. Or Perma Base. Anything but drywall.

My favourite backer board is Green EBoard. This is not drywall but as easy to work with.


Good luck.

JW
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Old 04-22-2012, 09:31 AM   #13
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Can I install Kerdi over primed drywall in a basement bathroom?


If you call Schluter when they refer to primer they do not mean a product you can buy at a paint store.

By primer they refer to an ad-mix product like Mapei's Planicrete AC or other products. Mapei's KeraBond does not list drywall as an acceptable substrate.

http://www.mapei.com/public/CA/produ...ond_TDS_EA.pdf

Custum Building Products allows drywall for their thinset only in dry areas

http://www.custombuildingproducts.com/TDS/TDS-193.pdf

Laticrete's 317 allows gypsum board in interiors only.

http://www.laticrete.com/Portals/0/d...ts/lds3170.pdf

Ardex has some amazing products and they also sell proper primers

http://www.ardex.com/cms/Assets/Prod...200411_WEB.pdf

Not to many options out there. Most of the setting materials companies do not allow the use of their products in wet zones. Drywall is not an approved backer board for either the TTMAC or the ANSI. You can order the specification guides for proper Canadian shower construction here http://www.ttmac.com/specifications.html or for American specification order your copy of the ANSI guide here

Before using any Kerdi over drywall first contact Schluter and ask to have a representative come out and inspect. Keep Schluter in the loop and ask their recommendation for both a proper primer and thinset. If they do not give you a specific product call the manufacture of your setting materials and ask them what product or products to use with Kerdi - you will find I'm sure with the exception of Ardex that the setting material companies want nothing to do with warranting an install with Kerdi over drywall.

Do your research and keep Schluter in the loop!

On Page 16 of the ANSI Specification guide it states that (3.5.1.1 Caution) Gypsum Board (ASTM C1396/C1396M), including water-resistant gypsum backing board, shall not be used in critical exposure areas such as exteriors, showers, saunas, or steam rooms.

The TCNA on page 25 of the 2011 specification guide has a backerboard selection guide. It lists Cement board, Coated Glass mat Water -resistant Gypsum backer board, Fiber-cement board, Fiber-Reinforced Water-Ressistant Gypsum Backer Board & Cementitoius Coated Extruded Foam Backer Board.

That's it.

JW

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Old 04-22-2012, 10:50 AM   #14
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Can I install Kerdi over primed drywall in a basement bathroom?


It's hard to follow your thinking; first, to generalize and say Schluter thinks that "a primer= an admixture" is way too far off-base. My guys sure know the difference...

Then you go on and quote thinset maufacturers who don't recommend using their products in wet zones. Nothing new there. Same for the TTMAC and ANSI guidelines...we know drywall is not an approved substrate to tile onto in a wet zone...Huh?

Then you quote guidelines that make no mention of Kerdi in their directions and are perhaps too narrow...

Forget about the data sheet and the specs; turn to Schluter for their advice on drywall in a shower and then fall back on your inspector if you have/need one. Up here some inspectors know about Kerdi, others don't. But most are bending Schluter's way and will allow drywall - unprimed - behind Kerdi, following their guidelines on, for example, the use of unmodified thinset.

If I were advising Michelle, at this late date, I'd say go ahead and apply unmodified thinset over the primed drywall. Then Kerdi.

Keep it simple.

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