Backerboard [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-11-2013, 09:31 AM
My wife and I placed cement backerboard this last weekend for shower walls.
I just today read on the internet that putting roofing paper over the studs first is necessary. Unfortunetly we didn't. My heart sank after reading that. Do we need to tear all the cement board back off and install this paper? We have one exterior walla nd two interior walls, all have insulation betweeen the studs. Any help would be greatly apprectiated.

Dan Dueker

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02-11-2013, 09:36 AM
While I am not an expert by any means, I just did this process within the last week or so. My understanding is that a vapor barrier between the stud and CBU is necessary...UNLESS, you plan to use a product like RedGard on the surface of the CBU. Since the CBU is already up, maybe that's the way to go so little-to-no water gets in behind the CBU.

Someone correct me if I am wrong...don't want to lead you astray.

02-11-2013, 02:12 PM
My understanding also reflects what Jeff said. Was there any plastic sheeting over the insulation?

HooKooDoo Ku
02-11-2013, 07:39 PM
From what I understand, Redgard (or similar) to waterproof the FRONT of the CBU is superiour to waterproofing behind the CBU. More expensive because a thick sheet of plastic is pretty cheap. But tile, thinset, and grout are not water proof. That is why you must put plastic behind the CBU. Eventually, water will make its way through the tile/thinset/grout and get the CBU wet. That wetness will penetrate the CBU and you want to keep that water off your studs. However, when you waterproof the FRONT of the CBU, the CBU never gets wet and your shower should dry out faster.

In my case, because I was getting all my supplies at Lowe's, I used AquaDefense (Mapei's product similar to RedGard available at Home Depot).

Donnie D.
02-11-2013, 07:44 PM
yes just use a liquid applied waterproofing membrane

02-12-2013, 05:57 PM
Perhaps another option would be to add Schluter's Kerdi membrane over the cbu? You can read about that on here.
The problem is that water vapour (Canadian spelling,lol) will get into the stud area and tend to condense in cold weather leading to the possibility of mold and mildew in that wall. I believe it is only the exterior wall you really need to be concerned with but there are other more knowledgeable folks on here.

Moral of the story is to do your research first! (smile :-)