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Old 09-05-2008, 01:04 AM   #1
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How many layers?


How many layers a rubber water resistant stuff does the drywall need in a bathroom before tiling? Should I add: oh wise ones...

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Old 09-05-2008, 08:02 AM   #2
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How many layers?


I'll get to the root of the question, but first...

You cannot use drywall behind tile in the wet areas of a bathroom, specifically tubs and showers. You must use cement backerboard (concrete sheetrock), and should tape and mud the seams with backerboard mesh tape and thinset.

There are a couple ways to waterproof the walls of a tiled tub, which is a must. Two are topical, and one isn't.

1) The backerboard can take moisture without degrading, so you can put a moisture barrier behind it. This is not ideal, but will probably get you by.

2) You can use an applied waterproofing agent like RedGard. You simply paint it over the backerboard once the board is hung and seams are taped/mudded. This stuff works great and is very DIY friendly. $50-80/gallon. One gallon will easily do even a large shower or tub area.

3) You can use Kerdi, which is a membrane made by Schluter. It goes over the backerboard on the wet side, and looks like sheet fiberglass. Pretty expensive, but is arguably the best system available.

Rubber membranes are sometimes used in shower mud pans under tiled floors, but not on walls.

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Old 12-28-2008, 12:48 PM   #3
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How many layers?


All of the studs are exposed. Before I put the backerboard up, do I need to put up sheetrock? It seems like over kill to use both sheetrock and backerboard.
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Old 12-28-2008, 01:18 PM   #4
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How many layers?


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All of the studs are exposed. Before I put the backerboard up, do I need to put up sheetrock? It seems like over kill to use both sheetrock and backerboard.
No

You use the backer board in place of sheetrock in the areas that will be receiving tile.
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Old 12-28-2008, 02:22 PM   #5
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How many layers?


After installing your backerboard you must do two things for a good installation.

1) Tape the backerboard seams and corners with mesh tape and thinset, just like you're mudding drywall. This prevents tile/grout cracking at the joints, which is basically inevitable if you don't do it.

2) If it is a tub or shower area, apply a waterproofing product to the backerboard to keep it from permeating moisture into the wall. RedGuard is a very common product and is easy to apply, and it is the least expensive method. Water WILL get through your tile and/or grout no matter what, so it must be properly managed.
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Old 12-29-2008, 10:29 AM   #6
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How many layers?


Are there any issues with putting insulation behind the backer board? Any requirements on what type of insulation to use (foam or fiber)?
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Old 12-29-2008, 10:40 AM   #7
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How many layers?


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Are there any issues with putting insulation behind the backer board?)?
No. In fact, this is often done for noise reduction (shower), especially if there is a bedroom located on the other side of the shower wall.

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Any requirements on what type of insulation to use (foam or fiber)?
I'd avoid using a kraft faced insulation if you are using a vapor barrier. Other than that, any kind of insulation will work. No specifications, unless the bathroom is located in a high humidity area like a basement.
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Old 12-29-2008, 10:48 AM   #8
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No. In fact, this is often done for noise reduction (shower), especially if there is a bedroom loacted on the other side of the shower wall.

I'd avoid using a kraft faced insulation if you are using a vapor barrier. Other than that, any kind of insulation will work. No specifications, unless the bathroom is located in a high humidity area like a basement.

It is actually located in a basement. Should be pretty well ventelated but there was termite damage before the remodel.
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Old 12-29-2008, 10:51 AM   #9
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It is actually located in a basement. Should be pretty well ventelated but there was termite damage before the remodel.
I'd suggest using rigid foam board insulation, if it is in your basement.
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Old 12-29-2008, 11:36 AM   #10
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How many layers?


Also, if you waterproof as per KCTERMITES suggestions (RedGard or Kerdi) you need to understand both of those act as vapor barriers also. If you use either, do not use an additional vapor barrier behind the cement backer as you will then create a moisture sandwich.
Personally I vote for waterproofing as the goal is to keep all moisture INSIDE the bathroom area. You can then use the unfaced fiberglass batts in the shower/tub area. Although a better option for insulating in a basement, I would not use the rigid foam around the shower because of the moisture sandwich situation. If you're tiling a non-wet location wall (outside of the tub/shower), there's no need to waterproof the wall before tiling and then the rigid foam will work just fine.
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Old 12-29-2008, 06:52 PM   #11
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FWIW and To Clarify: In terms of foam creating a moisture sandwich (which is caused by using two layers of vapor barrier/vapor retarder material); Rigid foam board, in and of itself, is not recogninized as a "vapor barrier". When used in certain areas/applications, it may still require a vapor barrier/vapor retarder facing.

"While rigid foam board can serve as the air barrier if it is properly cut, fit, and the joints and penetrations sealed, it cannot serve as the vapor retarder." - http://www.foam-tech.com/problems/exterior_wall.htm


Specific Examples Below(http://www.onlinetips.org/rigid-foam-board-insulation):

Molded Expanded Polystyrene Foam Board - MEPS foam board is available with a variety of facings. Since spaces between the foam beads can absorb water, a vapor diffusion retarder is necessary if water transmission through the insulation might become a problem.

Polyisocyanurate and Polyurethane Foam Board - Polyisocyanurate or polyiso and polyurethane are very similar, closed-cell foam insulation materials .... when used with a laminated aluminum foil facing, polyiso foam board provides an effective moisture or vapor barrier.

Extruded Expanded Polystyrene Foam Board - Extruded expanded polystyrene (XEPS) is a closed-cell foam insulation similar to MEPS....Extruded polystyrene also has excellent resistance to moisture absorption.
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Old 12-29-2008, 11:17 PM   #12
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Sorry AtlanticWB. I am by no means an insulation expert but I read this thread just before I went to a home improvement store earlier today. While there, I looked at their rigid foam. It was Owens Corning Foamular. I read the data sheet and it said it was virtually impervious to moisture. As that was the only rigid foam option at the store, that's what I based my statement off of.
Thanks for the further explanation of other types of foam.
When I insulate behind a shower/tub surround wall, we always waterproof, thereby creating a vapor barrier and insulate with the appropriate R value unfaced fiberglass batts.
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Old 12-30-2008, 10:06 AM   #13
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How many layers?


Thank you for all of the information. I'll try and post pictures this weekend.
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Old 12-30-2008, 10:20 AM   #14
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Although not listed or intended for use as a vapor/moisture barrier, foamboard will effectively perform like one in this application due to its general waterproof/impermeable properties and could lead to the aforementioned moisture sandwich.

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