Need Advice - Vapour Barrier Behind Shower Backerboard

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Ameds
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Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Ameds » Thu Mar 16, 2017 5:21 pm

My home builder is installing DensShield tile backerboard (http://www.buildgp.com/densshield-tilebacker-board) in our main shower stall, directly over the poly vapour barrier.

Can anyone let me know if this is the proper way of doing things? I've read a lot of comments about this being a recipe for mould down the road; although a lot of people are referring to cement boards. Anybody have experience with DensSheild? I live in a cold Canadian climate.

The installation instructions say "Do not install vapor barriers directly behind DensShield panels. DensShield has a built-in moisture barrier; a #15 felt behind the DensShield is permissible if required by local code jurisdiction."

Any advice is appreciated!

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Shannon
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Shannon » Thu Mar 16, 2017 7:19 pm

Its interesting that Denshirld says not to place over poly? Their product obviously lets lots of moisture through?
If the wall is an exterior wall then the poly is needed by code but maybe the installer needs to use spacers between the poly and the back of the Denshield? Really not sure if that will help or not? are you tiling the shower walls?
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Ameds
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Ameds » Thu Mar 16, 2017 7:44 pm

Yes, we will be tiling the shower walls.

I was also surprised with the recommendation in the installation guide not to place over poly. I called the technical support line and they told me to create a few slits with a utility knife in the poly before applying the DensShield to allow for any moisture that penetrates evaporate. I have an unsettling feeling about the whole thing.

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Aaron
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Aaron » Thu Mar 16, 2017 9:37 pm

Ameds wrote:Yes, we will be tiling the shower walls.

I was also surprised with the recommendation in the installation guide not to place over poly. I called the technical support line and they told me to create a few slits with a utility knife in the poly before applying the DensShield to allow for any moisture that penetrates evaporate. I have an unsettling feeling about the whole thing.
Yeah if code strictly requires a traditional poly barrier, then I think a different tilebacker should be used that doesn't have vapor-blocking properties.

The traditional material is Durock, which is porous and "breathes".

Stand up to your contractor before it's too late, you have a right to have this done right the first time!

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Shannon
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Shannon » Thu Mar 16, 2017 9:51 pm

I personally actually usually use moisture resistant drywall and then Schluter kerdi membrane over that under my tile showers or Kerdi board.
What ever you do do not cut the vapour barrier as they suggest. I'm even surprised they suggest that
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Aaron
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Aaron » Thu Mar 16, 2017 10:20 pm

So you go fiberglass > poly > green drywall > schluter membrane > thinset > tile/grout?

I'll have to research the Schluter products. I've seen them at Lowe's, I think.

Ameds
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Ameds » Fri Mar 17, 2017 5:42 am

I've been picking my battles with the builder, winning some and losing others. I don't think I'll be able to get them to replace the DensShield.

What I'm not understanding is: won't moisture be able to evaporate through the same path that it came in? Why does putting the DensShield over poly cause a problem?

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Shannon
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Shannon » Fri Mar 17, 2017 7:41 am

Ameds wrote:I've been picking my battles with the builder, winning some and losing others. I don't think I'll be able to get them to replace the DensShield.

What I'm not understanding is: won't moisture be able to evaporate through the same path that it came in? Why does putting the DensShield over poly cause a problem?
Yes I am kind of wondering the same thing actually. Also my thinking is usually you are using a ceramic tile (pretty nonporous) and if you use a good urethane or epoxy grout there should be pretty much no moisture traveling through anyways?
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Shannon
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Re: Need Advice - Vapour Barrier Behind Shower Backerboard

Post by Shannon » Fri Mar 17, 2017 7:42 am

Aaron wrote:So you go fiberglass > poly > green drywall > schluter membrane > thinset > tile/grout?

I'll have to research the Schluter products. I've seen them at Lowe's, I think.
Yes that is exactly it.
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