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ahreno 03-29-2009 03:03 AM

Tiling over green drywall?
My carpenter put up green drywall around my walk in shower. It seems to be a common consensus that this is not ideal. From what I can tell the best thing i can do at this point is to install kerdi over the top? The greenboard just went up and hasn't been taped or mudded yet. The shower is 34x48 so it wouldn't be a HUGE deal to pull out the green board and put up cement board / hardibacker.

what would you suggest? just take it down and put up cemet board/hardi backer or stick with the greenboard?

Also, we didn't put greenboard up ceiling of the shower... should we have?

Bob Mariani 03-29-2009 05:44 AM

Greenboard is no longer used in wet areas as it once was done. Why? Because time has shown that it did not work as expected. I would not use greenboard in any wet areas. The area above the shower head is not a wet area. The greenboard will be better than regular drywall for this area. CBU for the shower walls.

ccarlisle 03-29-2009 07:42 AM

Yes, "greenboard" is comparatively 'old technology' didn't really work in the first place - keeping moisture-ridden areas "moisture-free" and nowadays it has been passed - like slow truck on a highway -by newer technolgies viz: Kerdi or RedGuard or many other membranes.

But since it is up, leave it there. Don't waste it. CBU might have been a better choice from the beginning but the end result will be the same -ESPECIALLY if you are considering Kerdi. Now is the perfect time to award yourself a waterproof shower vs a shower that'll need replacing some 5 years from now.

Schluter (Kerdi) is a product that works so well that drywall (not even greenboard) is recommeded by the manufacturer - Schluter. CBU is fine too, but drywall is their #1 choice! Since Kerdi is a waterproof membrane, nothing goes through it and therefore you can put anything behind it - and drywall fits the bill. OK, greenboard if it's already up, it doesn't matter if it's green, blue or purple - all you need is structural support - not water resistance.

Greenboard is appropriate for the go ahead with that. BUT FIRST, find out whether whoever does the shower stall (a carpenter?) knows how to play with thinset and put up Kerdi. It's a piece of cake actually, so he should be willing to listen.

So, in summary, leave the greenboard - BUT ADD KERDI! Don't cheat yourself out of getting a 40 year shower warranty versus a 5 year "maybe".

ahreno 03-29-2009 11:03 AM

i just have normal drywall on the ceiling, should i pull it down and put up greenboard? or should i just kerdi over the top of the existing normal drywall? I don't recall seeing any 5/8" green board. I do have two holes (light and shower head) in the ceiling of the shower if that makes any difference.

R&D Tile 03-29-2009 11:20 AM

No kerdi on the ceiling unless this is a steam shower, tile or paint it, you'll be fine.

Bob Mariani 03-29-2009 11:52 AM

Be sure to use a sealed and covered light fixture approved for shower locations.

JazMan 03-29-2009 08:24 PM

I agree that a wallboard wall with Kerdi is the best way to build a shower. It's much better than a standard cement backer with no surface waterproofing.

As for the ceiling, actually regular drywall is better than green board because it is stiffer. Although most carpenters & drywall installers do not know it, green board is supposed to be fastened to ceiling joists that are 12" o.c., where regular wall board can span 24".

Find a few Kerdi showers I build here; :thumbsup:


ahreno 03-31-2009 10:51 AM

how hard will kerdi be to install?

ccarlisle 03-31-2009 05:08 PM

Go to and watch the video.

ahreno 04-03-2009 12:14 AM

I have a preformed shower pan. 34x48" I believe it's Jacuzzi brand. it's white and fiberglass. Can i still use kerdi?

747 04-03-2009 04:01 AM

He cheaped out on you. He should have installed cement board.

ahreno 04-05-2009 01:16 PM

He didn't cheap out on me. he's a good friend and wants things done right just as much as I do. It was an honest mistake and luckily we caught it early enough on. In his house he built his tile shower off greenboard and hasn't had a problem (that he knows about) yet.

Does kerdi work with a premade shower pan?

R&D Tile 04-06-2009 07:21 PM

Yes, it works, just seal it to the lip of the pan with Kerdi fix or 100% silicone.

ccarlisle 04-07-2009 07:07 AM

I don't know if Schluter has a guide for their products in shower pan assemblies - probably do but I can't find it - but manufacturers of wall panels, for example, Georgia-Pacific ( - have diagrams showing their products in shower pan assemblies. The panels come down over the flange of the pan and the gap that is formed is filled with caulking, as R&D points out. But if your greenboard is already up, tell us how it is configured with the pan...Normally the pan goes in first, because it is supported with thinset then the wall overlap the pan flanges.

Greenboard, so I understand, was popular and new in the early 70's - 35 years ago! - then cbu hit the market in the early 80's. We've come a long way since then. Greenboard may have been water-resistant (not waterproof) and therefore good for bathroom walls but not for showers. Moulds fed off the gypsum once it ate throught the wax coating they put on it...not a pretty sight. We don't see that much greenboard in showers - because showers made from it have long since failed. :wink:

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