# Do you need a vapor barrier behind hardiebacker?



## jayp

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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## Termite

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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## jayp

*thought so*

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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## Knucklez

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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## AtlanticWBConst.

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?reso...ts/prod_details/DUROCK_Brand_Cement_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.



jayp said:


> ...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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## JenkinsHB

jayp said:


> 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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## WallyPoppa

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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## Termite

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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## jayp

*I took the 1/4 back*

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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## Termite

Good decision, and good idea on the felt shims.


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## AtlanticWBConst.

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

Good job figuring that one out on your own. :thumbsup:


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## toddbailey

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?


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## Termite

toddbailey said:


> 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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## Gary in WA

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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## Grimace

jayp said:


> 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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## JRA773

*Listen to the guy at the flooring store!*

JAYP, the guy at the flooring store knows more than most of the people given you bad advice here! YOU DON'T NEED A VAPOR BARRIER WITH HARDIBACKER. It is not traditional cement board! Many of these people that replied to you here are saying they have the same characteristics and they don't! Hardibacker doesn't need a vapor barrier or waterproofing except you do need to tape and thinset the joints. Go right to the video from Hardibacker on Youtube and they'll show you how to do it properly. I only use Hardibacker on my jobs and it's been great. Less fuss and better performance. There are a lot of opinions out there, but remember most of them are coming from people that don't know what they're talking about.


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## JazMan

JRA773,

No wonder you didn't use a real name, you are the one that has no idea what you're talking about. You don't know, but you don't know that you don't know.:yes: So you might be forgiven if you study and learn. 

Hardie installation on wet walls require some type of vapor barrier just like any other backerboard. The barrier is to protect the wall cavity. Many of us like to use a surface waterproofing instead of plastic or tarpaper on the studs. I think a surface membrane is much better.

You obviously haven't had the time yet to read the Hardie directions, or maybe you missed it. You should have someone read them to you, especially the part that says; 

*3 | - Attach HardieBacker cement board to framing
• See applicable building codes regarding vapor barrier requirements.*

Go here: http://www.jameshardie.com/homeowner/pdf/backer-install-us.pdf
Pay little attention to videos that gloss over details, actually most don't mention the important stuff to make it look easier. 

I'm not gonna bother to read all those old posts that go back close to 5 years. I will if it will help though. 

So, you have your assignment, report back when you're ready.

Jaz


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## toddbailey

My 2 cents plus tax. Unless you are doing a bathroom or kitchen wall next to a water source such as a sink, tub/shower using a vapor barrier is optional, it is recommended however to use a vapour barrier in any bathroom, utility room (containing a washer /dryer) or kitchen. A floor or wall in a hallway, bedroom, entry way a vapour barrier is optional and usually unnecessary. It's best to contact a local governmental building agency and enquire on building codes. Whats true in one state may not apply in another


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## JazMan

Where else would you use concrete backer if not a tub surround or stall shower for a wall application? You're supposed to apply a vapor barrier either on the studs or better yet on the surface of the backer. It's not always done I know, but there's lots of things done wrong out there and there's lots of hacks doing work. Not following the rules does not mean an automatic failure though. 

Why do you mention a floor? Floors do not require a vapor barrier. 

Jaz


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## toddbailey

I used hardi-backer over my traditional particle board floor before I put down a tile floor.


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## JazMan

That's nice Todd, (and not a recommended substrate, that particle board), but no one's talking about floors. We're dealing with vapor barriers which are for walls in wet areas.

Hope that floor was OSB and not PT. PT should always be removed. Again it won't fail every time, but if PT gets wet a few times, be ready to sweep it up. Bad stuff. 

Jaz


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## toddbailey

JazMan said:


> That's nice Todd, (and not a recommended substrate, that particle board), but no one's talking about floors. We're dealing with vapor barriers which are for walls in wet areas.
> 
> Hope that floor was OSB and not PT. PT should always be removed. Again it won't fail every time, but if PT gets wet a few times, be ready to sweep it up. Bad stuff.
> 
> Jaz



I realize that, walls especially bathroom and kitchens, or even laundry rooms should use a vapour barrier. But I would want to check with the local agencies just to find out what code is, just so one can exceed it.

My home is a 1980's built mfg home, so they cut every possible corner imaginable. Then they cut even more corners. I replaced the vinyl and carpeted floors with 2 1/2 inch layers of wonder board, all glued and screwed in place with 6 inch screw spacing. I ran a center support to stiffen up the entire floor to be tiled with a 4x6 center support beam. 
The floor uses 3/4 inch plywood on 2x6 joists on 16 inch centers, but I did find a few areas where particle board was used. 
When I was done with the structural mods I put down radiant heating wire and floor tile. It's all very solid, and much better than the flex-o-matic original floor. No cargo decking was harmed during the construction of the home.


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## JazMan

I'm glad it worked out for you. Why did you use two 1/2" layers of WonderBoard? That did nothing for the structure aside from making it heavier and higher. You should have added plywood then the concrete board if you needed the additional height. 

Jaz


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## toddbailey

JazMan said:


> I'm glad it worked out for you. Why did you use two 1/2" layers of WonderBoard? That did nothing for the structure aside from making it heavier and higher. You should have added plywood then the concrete board if you needed the additional height.
> 
> Jaz


I didn't mean to hijack this post, but I wanted the structural and thermal properties that only a concrete based product could provide.
In retro-spec, however, I probably could have just put down cargo decking and plywood, but time and cost were factors


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## oldhouseguy

Hey Jazman...

It might be worth pointing out for others that may find this thread that when you do a tub surround, you don't want vapor barrier behind and then ALSO a waterproofing product or membrane over the substrate. 

Some people do this to be extra sure of their waterproofing.

This I believe would leave nowhere for any moisture that did get through the membrane to go.

This in my mind is where you would get the mold sandwich.

Am I right about this?


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## JazMan

Absolutely right, you don't want 2 vapor barriers and a mold sandwich. I highly recommend going with the surface membrane. On a tub surround, two coats and/or the specified mil thickness of a liquid membrane is good. For showers I like Kerdi with the Kerdi Drain. 

Most people end up doing nothing, they just don't know what to do. A few years later they have mold and mildew in the lower corners and trouble keeping it all clean.

Jaz


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## John28

jayp said:


> The Hardiebacker brochure says not to apply waterproofing to the face of it because it will not allow the thinset to adhere properly.


Just curious, where you read this?

I'm in the final stages of a traditional shower pan with Hardie walls and did a great amount of research, and never came across that? But did find plenty of advice for using a barrier with Hardie in wet areas. So I went with a waterproofing Hydro Ban on the hardie, and the thinset seemed to bond very well to it?

I know many were having issues with Red Gaurd, which might be the reason, they were saying no waterproofing? I purposely steered away from Red Gaurd, and went with Hydro Ban, which I couldn't even srape off a piece of test Hardie I coated. So far the tiles have bonded well to the Hydro Ban, not sure where you read that, but hope my tiles don't fall off?


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## toddbailey

I no expert on this but I think the vapor barrier goes between the wall studs and the hardibacker wall board. At least that's what I found on a previous tile bathroom wall installation


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## JRA773

Jaz man, I’m not trying get personal and it seems you are, and I’m certainly not trying to hide behind a username. I was just trying to help a beginner who seemed confused since he’s been told 2 different things. 

My code doesn’t require a vapor barrier and my point is you don’t need one with Hardibacker by the nature of it’s composition. Your plain wrong on them requiring a barrier - their directions say “check your local code” and doesn’t say you absolutely need it. Why would they leave that out of their installation videos if you really needed it? 

They specifically say not to use a Redguard or similar waterproofing on the face as it will not allow thinset to bond as well. I’ve had a number of pro tilers tell me they never install a vapor barrier behind or waterproof the front of Hardi-backer. It's already waterproof. To say you must have a vapor barrier with Hardi is just not true. Now again, I'm talking about tub surrounds, not pans.

To say an installation may fail w/no barrier is nuts. We've all seen 30-40 year old homes with tile that was just stuck to regular old drywall with mastic
in a tub surround and no leaks or mold. Of course, I don’t condone this, but my point is it’s still on the walls and in decent shape.


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## oh'mike

Hardibacker is not waterproof----water will not damage it--however water will absorb into it and eventually soak right on through.

A vapor barrier is required---either on the face of the studs or better yet--a water proof membrane on the exposed face of the backer board---

Where did you hear that Hardi was waterproof?


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## toddbailey

oh'mike said:


> Hardibacker is not waterproof----water will not damage it--however water will absorb into it and eventually soak right on through.
> 
> A vapor barrier is required---either on the face of the studs or better yet--a water proof membrane on the exposed face of the backer board---
> 
> Where did you hear that Hardi was waterproof?


You are confusing moisture resistance with a flooded area.
Eventually is the key here, and you'll have more issues to deal with by the time the board is fully saturated. HardieBacker board provides superior protection against moisture damage and mold growth and is backed by a limited lifetime product warranty.


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## JazMan

JRA,

Concerning being personal and giving advice: You are the one who said;



JRA773 said:


> JAYP, the guy at the flooring store knows more than most of the people given you bad advice here!


You then yelled out;


JRA773 said:


> YOU DON'T NEED A VAPOR BARRIER WITH HARDIBACKER.


That of course is all wrong. Even in the few areas where a vapor barrier isn't mandatory, (I believe in parts of Louisiana because of the high outdoor humidity and often no insulated walls) It's advisable to apply a surface membrane so the substrate does not get wet. 



JRA773 said:


> They *specifically *say not to use a Redguard or similar waterproofing on the face as it will not allow thinset to bond as well.


No they don't! Hardie says no such thing! I read it the other day, can't find it now, but they're not talking about a waterproofing membrane. Products like Redgard and Hydro-Ban are made specifically to provide an excellent base for thinset. 



JRA773 said:


> I’ve had a number of pro tilers tell me they never install a vapor barrier behind or waterproof the front of Hardi-backer.


That is absolutely true. I recommend you not use them since they learned wrong and have not yet realized that mold is not a good thing and can easily be prevented with these products and methods. 




JRA773 said:


> To say an installation may fail w/no barrier is nuts. We've all seen 30-40 year old homes with tile that was just stuck to regular old drywall with mastic in a tub surround and no leaks or mold. Of course, I don’t condone this, but my point is it’s still on the walls and in decent shape.


I've seen those walls too. Some had no barriers at all. Most were mud jobs though and that's a different deal. The 3/4" of wall mud can absorb the little moisture that penetrated, then it was allowed to evaporate with no damage. Todays wall assemblies are much different. 

The sheet & liquid membranes have been developed because of all the problems associated with the low quality work you're describing. 

You have the same theory as some hacks. I'm thinking you're not, since you at least have checked for minimum codes in your area apparently. They cut corners and get away with it and so that's their new standard. Of course doing a job wrong, or skipping a step does not necessarily mean it's going to fail. There are manufacturer's specs and industry standards such as ANSI & TCNA that every tile setter should follow. Every trade has its standards. 

Jaz


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## Gary in WA

"Although cement backers are unaffected by moisture, they allow the passage of moisture through to the wall cavity if no additional moisture barrier is used. With DensShield Tile Backer, no additional moisture barrier is required or recommended." From; http://docs.google.com/viewer?a=v&q...UHPD96&sig=AHIEtbRqwCDcu8AJUye5WlK87HmnplLw0w

In that same article, cement board wicks up 3" water in 24 hours time, D.S. wicks only 3/8".

Gary


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## toddbailey

In the final analysis, 

it's best to speak with the building inspectors, L&I and general building contractors in your area and find out what is code, what is required, what is disapproved. ASK QUESTIONS !!! what's ok here may not be ok there.


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## kevino2640

JRA773 said:


> Jaz man, I’m not trying get personal and it seems you are, and I’m certainly not trying to hide behind a username. I was just trying to help a beginner who seemed confused since he’s been told 2 different things.
> 
> My code doesn’t require a vapor barrier and my point is you don’t need one with Hardibacker by the nature of it’s composition. Your plain wrong on them requiring a barrier - their directions say “check your local code” and doesn’t say you absolutely need it. Why would they leave that out of their installation videos if you really needed it?
> 
> They specifically say not to use a Redguard or similar waterproofing on the face as it will not allow thinset to bond as well. I’ve had a number of pro tilers tell me they never install a vapor barrier behind or waterproof the front of Hardi-backer. It's already waterproof. To say you must have a vapor barrier with Hardi is just not true. Now again, I'm talking about tub surrounds, not pans.
> 
> To say an installation may fail w/no barrier is nuts. We've all seen 30-40 year old homes with tile that was just stuck to regular old drywall with mastic
> in a tub surround and no leaks or mold. Of course, I don’t condone this, but my point is it’s still on the walls and in decent shape.


 back in the good old days homes were made with plaster on the inside no mold would grow no matter what then they came out with drywall a substance mold loves to grow on stachibautrous a poisonous type of mold loves drywall will grow when drywall gets wet. So mold and moisture are much more of a beg deal now. 
every competent tile man will tell you that a vapor barrier is needed between the studs and hardie backer 

if you want to know if hardiebacker is water proof just take a bucket cut a hole in the bottom glue the bucket to the hardiebacker and poor 8 ounces of water in the bucket. if the water goes through the hardie backer in less than 7 days obviously it is not water proof.


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