# Can closed cell spray foam be used as a water proof vapor barrier in a shower?



## Mike Finley (Apr 28, 2004)

Can closed cell spray foam be used as a water proof vapor barrier in a shower by spraying all the bays completely?


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## angus242 (Oct 20, 2007)

Well I suppose the answer is yes. But.....
If you're waterproofing the shower walls, you are then creating a "moisture sandwich" condition. I looked into this exact situation last year after I had 2 bathroom remodels in a row that had inadequate insulation between the bath tub/shower wall and the exterior. After talking to different companies, I decided the best route (for my geographical environment) was blown cellulose for the exterior wall and then waterproof the shower walls. 
For us, that means DensArmor in the entire bathroom, covered with Kerdi in wet locations.


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## Mike Finley (Apr 28, 2004)

Yeah, the moisture sandwich is kind of what I'm looking for. (sort of)


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## angus242 (Oct 20, 2007)

I talked with spray foam installers (no help, just told me how wonderful their product is), Schluter (said thought closed cell was bad idea but wouldn't affect Kerdi), GP/DensArmor said to use Denshield (no thanks) and finally after talking with GreenFiber (cellulose), decided that was the way to go since they don't recommend a vapor barrier with their product regardless of what's on the interior wall (above grade).

Of course they are many other products that can successfully used in place of the materials we use. I cannot comment on any of those situations. 

We are very pleased with the Kerdi/DensArmor/GreenFiber method :thumbup:


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## Mike Finley (Apr 28, 2004)

Yeah, essential you are putting the moisture barrier on the shower side of the project. Tile goes on it, water penetrates grout and dries to the shower side, no moisture passes into the walls.


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## mics_54 (Oct 28, 2008)

excuse me? a moisture sandwich? wtf


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## angus242 (Oct 20, 2007)

mics_54 said:


> a moisture sandwich?


I think it's on Subway's $5 menu :laughing:

..wait a minute :blink:


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## ChrWright (Jul 17, 2007)

I'll have mine with fries, please.


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## SLSTech (Sep 13, 2008)

As a vapor barrier - no
If the Closed Cell Foam is applied properly though you should have no issues with a moisture sandwich


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## angus242 (Oct 20, 2007)

SLSTech said:


> As a vapor barrier - no
> If the Closed Cell Foam is applied properly though you should have no issues with a moisture sandwich



I am NOT an expert on this so that's why I ask the manufacturers. This is a reply I got from one of the closed cell foam manufacturers:

_"Closed Cell foam is a Code Approved Vapour Barrier with a permeability rating of under 45 ng, as well as a Code Approved Air Barrier and Thermal Insulation. Closed Cell foam is spray applied as a liquid to create an air-tight seal as it expands as a foam to stop air leakage. But unlike Open Cell foam, Closed Cell foam stops both convection through and within the wall cavity"
_
From the materials/replies I received, it was my opinion that I'd rather not play with closed cell foam insulation because even if it is not a 100% vapor barrier, it would still retard the dehumidification process enough for me to not use it. 

Mind you, I'm talking about an exterior wall to shower enclosure in my climate. For me, the Kerdi is enough to keep moisture in the shower and the cellulose is enough insulation to keep the cold out, yet still breath. 

I'm all ears if you have some different info!


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## neolitic (Apr 20, 2006)

angus242 said:


> I am NOT an expert on this so that's why I ask the manufacturers. This is a reply I got from one of the closed cell foam manufacturers:
> 
> _"Closed Cell foam is a Code Approved Vapour Barrier with a permeability rating of under 45 ng, as well as a Code Approved Air Barrier and Thermal Insulation. Closed Cell foam is spray applied as a liquid to create an air-tight seal as it expands as a foam to stop air leakage. But unlike Open Cell foam, Closed Cell foam stops both convection through and within the wall cavity"
> _
> ...


I have always wondered, if one is depending 
on the foam to act as vapor barrier/retarder,
what happens on the face of the studs?


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## angus242 (Oct 20, 2007)

neolitic said:


> I have always wondered, if one is depending
> on the foam to act as vapor barrier/retarder,
> what happens on the face of the studs?


Yep. Good point and another reason to keep moisture inside the shower and let the exterior wall breathe.


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## mics_54 (Oct 28, 2008)

well solid wood 3.5 inches thick probabaly has a fairly low perm rating however the joints, cracks and voids in the assembly more than likely makes it moot. SOME sprayed in foams do rate as vapor barriers and in places where better means is impossible it's a good solution (rim joists for instance) I guess the terms moisture barrier and vapor barrier could be used synominously in some applications but not necessarily all. 
I would be more inclined to use foams, rigid or otherwise, to gain maximum insulative value per inch and install a moisture barrier that would serve as a vapor barrier also, on the warm side of the wall space.


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## SLSTech (Sep 13, 2008)

Angus I am a little confused on your comments, or maybe I just didn't state mine fully

CC Foam can be used as a vapor barrier - but everything would have to be covered including the studs to make it a true barrier required for use in a CT shower

Why do you need the wall to breathe while using Kerdi? The vapor can't get past it, & you do not have the thermal transfer that creates the condensation issues

Is that clearer or did I just make it worse?


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## davitk (Oct 3, 2008)

The UDC approves CC foam as a vapor _retarder_ as long as double studs, plates, etc are caulked.

Now a _water proof_ membrane is another animal altogether...

Moisture sandwich. Sounds yucky.


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## angus242 (Oct 20, 2007)

SLSTech said:


> Angus I am a little confused on your comments, or maybe I just didn't state mine fully
> 
> CC Foam can be used as a vapor barrier - but everything would have to be covered including the studs to make it a true barrier required for use in a CT shower
> 
> ...


Got it now. I've had one helluva day..........:sad:


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## JohnS (Oct 9, 2009)

It would take a large amount of closed cell foam to create a truly waterproof surface. Closed cell foam is a vapor retarded by technical definition. The closed cell foam is very, very great at resisting moisture, however it will not completely stop all penetration of moisture. Under most normal circumstances it would do more than an a adequate job.


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