Vapour Barrier behind Denshield? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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10-14-2003, 10:36 AM
I am interested in installing Denshield as my tile backer in my new shower but I have two walls of the shower that are outside walls and are insulated with a vapour barrier installed. I have heard that when using Denshield a vapour barrier should not be installed behind it. Is this true? Should I remove the vapour barrier on my two insulated walls and install the Denshield tile backer or can I keep the vapour barrier in place?


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10-14-2003, 11:07 AM
Welcome, Ranger. :)

Give us a first name to use, will ya? Peoples will get askeered if they see Ranger, thinking it's the Tile Ranger who drops by here from time to time to chastise tile wrongdoers. :eek:

I'll start the bidding here:

1. Lose the Denshield. Install a CBU on the walls of your shower.

2. If your "vapor barrier" is a polyethylene sheet installed over the studs, leave it in place (assuming CBU instead of Denshield); if you have Kraft paper-backed insulation instead, I recommend slicing it with a razor blade a number of times and installing a polyethylene moisture barrier over the studs behind your backer board.

We have discussions about this on a regular basis. You can do a search and read some of the varying rationales. What you are trying to prevent, in any case, is a moisture "sandwich" between any two relatively impervious barriers.

10-14-2003, 12:45 PM

Thanks for the reply. No I am not the 'Tile Ranger' you referred to. First time visiting this forum so I'm not familiar with some of the other user names. My first name is Greg, by the way.

Regarding the vapour barrier it is polyethylene and not paper and I would really prefer to keep it in place which is why I posted the question.

As for the other comment about using a CBU instead of denshield, are you saying that the denshield is a poor product or just not worth the extra expense. I have no real preference other than the denshield is lighter and seems easier to work with. So why do you recommend the CBU instead of the Denshield?

10-14-2003, 02:39 PM
Denshield has a waterproofing fabric on the surface of the board. When nailed, one nails right through it. Granted one is supposed to use their special tape and sealing compound, but most of the guys here do not use it.

By the way, I have never used it; don't know why, just never have. I was a wonder board guy for 20 years, and just switched to Hardibacker.

If I was going to install the stuff, I would cal the manufacturer and get their opinion off their Web Site or from Technical Service.

John Bridge
10-14-2003, 07:20 PM
Hi Greg, Welcome. :)

The only thing Denshield has going for it is that it's easy to cut and it's lighter than cement board. Those are not good reasons to use it. Use Hardi-backer or any of the cement backer boards -- Durock, Wonder Board, Perma Base, etc.

Schluter Kerdi over gyp rock/sheetrock is also a good way to go.

01-06-2006, 12:50 PM
I would never use a plastic sheeting behind any cementuous backer board They all weep water and moisture and this is trapped behind the board. I have ripped down at least 6 jobs where mildue was running rampid behind the walls. In some communities the codes will not allow this practice.

01-06-2006, 01:30 PM
Hi there arturotile, I suspect quite a few members here will disagree with your comment re. not using vapor barriers behind CBU.

Although I probably should ask: Are you opposed to placing a vapor barrier of any kind behind cement backerboards? Or are your comments specifically directed toward using plastic sheeting as the barrier, with something else like roofing felt meeting with your approval?

I'll certainly agree with your statement about water/moisture readily permeating through backerboards. Where would you rather have that water go? Into the stud bay, onto the sole plate, sub-floor, and other framing members below?

01-06-2006, 04:37 PM
I would suggest that you might try Tyvek if you are looking for an alternative to roofing paper. One big advantage is that it comes in 9' widths like poly.

Brian Wallace A Cut Above

01-06-2006, 05:27 PM
Well Brian, one of the main advantages of Tyvek is, it's vapor-permeable. Which incidently is exactly why the exterior of a building can be wrapped with it. It has other attributes as well certainly but acting as a vapor barrier would not be one of them. :shake:

01-06-2006, 08:05 PM
I suspect quite a few members here will disagree with your comment re. not using vapor barriers behind CBU. One dissagreeing member voting here. Well, in favor of a moisture barrier, at least. :)

That moisture that gets behind the CBU has the option of getting back out the same way it got in there, Arturo, eh?

As for the Tyvek, I think it would probably be a good application for it. We're not really installing a vapor barrier behind the CBU anyway, even though the term is frequently used. What we really need is a moisture barrier, which Tyvek would do nicely. And that would give people one good reason to buy it on accounta I can't think of any other in my part of the country.

And being somewhat breathable, like roofing felt, isn't a big negative unless you're building a steam shower.

My opinion; worth price charged.

01-07-2006, 01:34 AM
Hmmmm....sure you would want Tyvek in your shower CX? :shades:

Poly's gonna have a perm rating below 1, maybe .6 or so. Felt will come in around 6 if I remember correctly. Tyvek on the other hand has a perm rating up around 58....sure you would want Tyvek in your shower CX? ;)

01-07-2006, 11:10 AM
Well, truth be told, I didn't know Tyvek's perm was that high, Mike. But roofing felt, I think, starts out at about 4 when dry, but increases to something around 30 when wet, if memory serves. Memory don't serve as well as it once did, of course. :crap:

Me, I use poly. But when you poke lotsa holes inna poly to attach it to the wall, the rating decreases substantially, specially when used behind lath for mud. But it's still a good moisture retarder and drain plane.

But your point is well taken.

My opinion; worth price charged.