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Old 06-06-2008, 07:38 AM   #1
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Do you need a vapor barrier behind hardiebacker?


As I type this I'm wondering if anyone is going to laugh but sometimes people will tell me one thing and I'll believe another until the whole topic becomes cloudy.

I went to pick up some sheets of hardibacker for a wall tiling project in a bathroom shower nook and the guy in the flooring section proceeds to tell me that I do not need to apply a vapor barrier to the stud wall with hardibacker as long as I tape and mortar all my seams. It sounds plausible but I don't know... He said it would trap moisture between the backerboard and the plastic. Likewise, I told him that one of the shower walls is an exterior wall and he said to use unfaced insulation so as not to trap moisture between the backboard and the paper on the inside face of the insulation.

Is there truth to this or should I disregard and use plastic? I have some 4 mil clear plastic I was thinking of using.

And, I've just been reading that some people are against applying hardibacker directly to studs. Sometimes I see people saying to use greenboard first, then backer. My studs are 16" OC and the backer I have is 1/4 " thick. Will this be sturdy enough?

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Old 06-06-2008, 08:56 AM   #2
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Do you need a vapor barrier behind hardiebacker?


The guy at your supplier is full of it. You need to install a vapor barrier to the studs at the very least, and you must alway mud and tape the seams with fiberglass cement backerboard tape. Backerboard is water-permeable, and will not stop moisture from entering the wall cavity.

The best practice is to waterproof the face of the backerboard with a product such as redguard or proguard HDG. With that, you can skip the vapor barrier.

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Old 06-06-2008, 10:53 AM   #3
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Do you need a vapor barrier behind hardiebacker?


He told me Hardiebacker isn't water permeable so I shouldn't install a barrier because it would create a "mold sandwich" between the plastic and the backerboard. Would 4 mil plastic be a decent vapor barrier? The Hardiebacker brochure says not to apply waterproofing to the face of it because it will not allow the thinset to adhere properly.
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Old 06-06-2008, 11:05 PM   #4
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Do you need a vapor barrier behind hardiebacker?


for water area like tub/shower you should put 15lb felt on the studs and then the hardibacker. screen & mud all seems.
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Old 06-07-2008, 06:55 AM   #5
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Do you need a vapor barrier behind hardiebacker?


The person you spoke to at the store, is giving out wrong advice.

Cement board is in no way, shape, or form....any kind of a vapor barrier, nor is it rated as such. Thus, it cannot be a "membrane" in a vapor chamber, that the person you spoke to, insinuated.

As an example, from Durock's website (http://www.usg.com/navigate.do?resou...ment_Board.htm):
"Durock (Cement)Board is "Water durable" - will not rot, warp, delaminate, or disintegrate when exposed to water."

Cement board, or fiber-cement board, will not breakdown with moisture, like the way sheetrock does. In that way, it is superior. However, like all cementitious material, the product is water permeable, it will take-in/absorb moisture, when it comes in contact with it. This will then be transferred to other surfaces that it comes in contact with. Thus, the need, for a good vapor/moisture barrier, and as suggested, a complete sealing of the installed board's seams themselves.

FWIW: Even Hardiplank fiber-cement siding board requires a good house-wrap (breath-able moisture barrier) behind it, when installed onto homes.

Quote:
Originally Posted by jayp View Post
...And, I've just been reading that some people are against applying hardibacker directly to studs. Sometimes I see people saying to use greenboard first, then backer. My studs are 16" OC and the backer I have is 1/4 " thick. Will this be sturdy enough?
1/4" Cement board is installed onto sub-flooring, for tile/stone installations. It is not for walls.

1/2" cement board, is attached directly to the studs, and it is never attached over greenboard.
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Last edited by AtlanticWBConst.; 06-07-2008 at 07:07 AM.
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Old 06-08-2008, 07:16 PM   #6
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Do you need a vapor barrier behind hardiebacker?


Quote:
Originally Posted by jayp View Post
He told me Hardiebacker isn't water permeable so I shouldn't install a barrier because it would create a "mold sandwich" between the plastic and the backerboard.
so he's recommending making a "mold sandwich" between your hardie board and your exterior sheathing? bad idea. seal that shower as tight as a frogs behind.
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Old 06-10-2008, 10:21 PM   #7
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Do you need a vapor barrier behind hardiebacker?


Bring back the HardiBoard. Exchange for 1/2 inch DenShield. Its impervious to water, needs no vapor barrier (built-in) and is lighter to handle and really and truly scores and snaps easily. It's a Georgia-Pacific product, part of their line of mold resistant wall and tile backer board.
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Old 06-10-2008, 10:25 PM   #8
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Do you need a vapor barrier behind hardiebacker?


DensShield is a good product, but isn't a revolutionary replacement for cementitious backerboard. No need to take the wonderboard back unless you want to.
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Old 06-11-2008, 07:01 AM   #9
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Do you need a vapor barrier behind hardiebacker?


I returned the 1/4" Hardie and got 1/2" Hardie. I stapled 4 mil plastic all the way to the floor, installed my new tub, and now I'm gonna attach the Hardiebacker. I had to compensate for the tub lip with some kind of furring because it's about 1/8" thick so I cut strips of heavy roofing felt and stapled them to the studs. I tried to table saw some 2x pieces but they were too brittle to screw the backerboard through. The roofing felt was a weird idea but it cut easily and did a great job allowing a transition from the 2x4 walls to the tub lip!
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Old 06-11-2008, 08:53 AM   #10
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Do you need a vapor barrier behind hardiebacker?


Good decision, and good idea on the felt shims.
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Old 06-11-2008, 04:38 PM   #11
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Do you need a vapor barrier behind hardiebacker?


FWIW: We always furr out the shower walls to accomodate the tub lip.

Good job figuring that one out on your own.
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Old 08-06-2009, 12:26 PM   #12
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Do you need a vapor barrier behind hardiebacker?


Taking this question a bit further, do I need a vapor barrier for a tile flooring project? (in a dining room, kitchen & foyer)

Home depot experts(?) suggested it as optional.

If I don't what are possible issues later?

I'm installing over plywood and also I needed more sub-floor stiffness. Manuf home ya know.

Starting out with 5/8 plywood, on 2 ft centers, 2x6 joists with 60 inch spans.
A bit narrow, perhaps; but I added a a couple of 12 ft 4x6 center beams with supports in 3 places w/ 4x4 posts & pier blocks, other wise a bouncy 10 ft span would exist.

I put down 2 layers of the 1/2 hardiebacker, making sure all the seams were staggered. I also used screws with 12 in spacing and around seams. also made sure I was hitting joists with 2 1/2 inch screws,
everything else were 1 5/8 in.

of course I used tape and mortar to seam the boards together.

the top layer (hardiebacker) was thin set to the first layer of hardiebacker and more screws were also used. No thin set was used for the plywood and backer board layer


Opinions on my install so far?

Last edited by toddbailey; 08-06-2009 at 12:29 PM.
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Old 08-06-2009, 05:18 PM   #13
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Do you need a vapor barrier behind hardiebacker?


Quote:
Originally Posted by toddbailey View Post
Taking this question a bit further, do I need a vapor barrier for a tile flooring project? (in a dining room, kitchen & foyer)

Home depot experts(?) suggested it as optional.

If I don't what are possible issues later?

I'm installing over plywood and also I needed more sub-floor stiffness. Manuf home ya know.

Starting out with 5/8 plywood, on 2 ft centers, 2x6 joists with 60 inch spans.
A bit narrow, perhaps; but I added a a couple of 12 ft 4x6 center beams with supports in 3 places w/ 4x4 posts & pier blocks, other wise a bouncy 10 ft span would exist.

I put down 2 layers of the 1/2 hardiebacker, making sure all the seams were staggered. I also used screws with 12 in spacing and around seams. also made sure I was hitting joists with 2 1/2 inch screws,
everything else were 1 5/8 in.

of course I used tape and mortar to seam the boards together.

the top layer (hardiebacker) was thin set to the first layer of hardiebacker and more screws were also used. No thin set was used for the plywood and backer board layer


Opinions on my install so far?
You made a big mistake using two layers of hardibacker. With 24"oc joists your floor sheathing is not stiff enough for installation of most tile, even if you've got the joists supported to limit or eliminate their deflection. Under foot you've done nothing to eliminate the sag of the floor sheathing and backerboard between the joists...That equals cracked grout and maybe even cracked tile.

The addition of backerboard lends no additional stiffness to the floor. Ideally you'd have added a layer of 1/2" plywood (or even 3/4") and used 1/4" backerboard under the tile.

You can apply the backerboard directly to the plywood using thinset, and that is the normal installation method. The wood may suck a little water out of the thinset the backerboard is set in but it usually won't cause problems.
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Old 08-06-2009, 06:25 PM   #14
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Do you need a vapor barrier behind hardiebacker?


In the earlier post isn't the plastic on the exterior wall supposed to go down over the tub's drip edge? Any water condensing now will rot the floor under the tub at the bottom of the wall. The plastic would not be necessary below the tub lip on an exterior wall as the tub would act as the vapor barrier. Or what? Be safe, G
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Old 08-07-2009, 01:45 PM   #15
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Do you need a vapor barrier behind hardiebacker?


Quote:
Originally Posted by jayp View Post
I returned the 1/4" Hardie and got 1/2" Hardie. I stapled 4 mil plastic all the way to the floor, installed my new tub, and now I'm gonna attach the Hardiebacker. I had to compensate for the tub lip with some kind of furring because it's about 1/8" thick so I cut strips of heavy roofing felt and stapled them to the studs. I tried to table saw some 2x pieces but they were too brittle to screw the backerboard through. The roofing felt was a weird idea but it cut easily and did a great job allowing a transition from the 2x4 walls to the tub lip!
thats not correct is it? (same question as GBAR)

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