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Unread 03-02-2013, 08:45 PM   #1
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Kerdi Board - Cement Board - Gypsum?

Hi there,
I have read through many of the posts and I have a question. I'll be constructing a new house in the Spring and want to build a tiled shower. Is there any suggestion as to what's the most suitable substrate for the tile? Is Greenboard with a Kerdi membrane sufficient or would you recommend using cement board with the Kerdi membrane. I'm just wondering why you would need to use cement board if the Kerdi membrane is waterproof?
Thanks in advance for taking the time to reply.
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Unread 03-02-2013, 09:35 PM   #2
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Hi Paul, welcome to the forum.

Drywall is the manufacturer's recommended substrate. Plain drywall, not greenboard. Greenboard is regular drywall with a water resistant coating applied to it. You might think that it would be slightly better than plain drywall. But the water resistant coating is extremely minimal. And the fact that the coating is something of a "bond breaker" that diminishes the bond to it, it's not worth using. I'd only use greenboard if the code in your municipality demands it.

Some folks really, really want to use cement board. If you feel compelled, go ahead. But the membrane is indeed waterproof and you should feel comfortable using the manufacturer's recommendations when they are the folks issuing a very solid warranty.

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Unread 03-02-2013, 10:11 PM   #3
Bodie Powers
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For added insurance, we always use CBU for the wet wall up to the shower head regardless of the waterproofing system. The concern is not a leak in the waterproofing but a leak in the plumbing and it's potential impact on the substrate.
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Unread 03-02-2013, 10:41 PM   #4
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yeah i did the drywall on 5-6 Kerdi showers and then went back to the CBU.

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Unread 03-02-2013, 10:46 PM   #5
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Depending on local rules, some will give you grief using drywall even though the manufacturer recommends it and has test data to prove it is more than adequate. It works just fine either way. Regardless, don't let the drywallers mud the joints in the area where the Kerdi would be going. The Kerdi membrane works better, and drywall mud isn't the greatest thing underneath it with the thinset. KerdiBoard works too and then you only need to band the seams and treat the screw fastener penetrations.
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Unread 03-03-2013, 04:15 AM   #6
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Nothing wrong with kerdi over a cbu. The manufactures of green board asked to be not included in the code. If they don't want their product used for showers, why would anyone else?
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Unread 03-03-2013, 06:39 AM   #7
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Condensation or plumbing leak as said above are really the only two ways your drywall could be damaged from behind.

If you are concerned about this than use Kerdi- board. But drywall with Kerdi properly installed will work beautifully.
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Unread 03-03-2013, 07:35 AM   #8
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Great advice you guys! Thanks so much! Will let you know how the build goes, just in the planning stages right now... Although cement board is a lot heavier and more of a pain to install, I will be going this route for the whole shower area and covering it with the Kerdi membrane. Thanks again, greatly appreciated!
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