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bigphil 09-26-2011 06:01 PM

Insulation type needed if using RedGard waterproofing?
Hello everyone! First off, I would like to say this forum is pretty cool! This is my first post, but have gleaned some good information from here already. So here is my sitution....
I am remodeling my bathroom and am trying to do it correct because whoever remodeled it years ago was an idiot :furious: I am no expert on building, but common sense apparently wasnt part of this persons genes.

So my question is this...I have an alcove that has two exterior walls where the tub will be going and I plan to use hardiebacker 1/2" for the entire wet area (including ceiling) and it will be tiled. I plan on using RedGard waterproofing membrane over the cbu, but not sure of what type of insulation to use behind the cbu for the exterior walls. Right now I have some new Certainteed R-15 in there with the paper facing on it, but I THINK the paper is also a vapor barrier, so I dont want to cause a situation with moisture build up between the cbu and insulation by having essentially a double vapor barrier. Should I remove the paper facing from the insulation or is it ok to keep it there when using Redgard?

ccarlisle 09-28-2011 10:57 AM

Well, the theory goes that a waterproofing membrane such as RedGard will, if installed properly, prevent any vapour from diffusing across the cbu and into the wall structure where, in cold months, it will condense to water. As such, the problem 'goes away' in that no vapour=no problem...and therefore no vapour retarder behind the cbu is needed. Insulation yes - but no vapour retarder; I subscribe to that theory so I'd say either remove the little bit of faced insulation you have, or remove the paper facing of it...

But since you're already there, why not upgrade to Roxul mineral wool, if buying a bag isn't too much for you to use? If so, then buy a small bag of pink fibreglass insulation and be done.

Not too sure where you're located but this should hold up pretty well anywhere...

Bud Cline 09-28-2011 11:43 AM

I would agree with the above but take it one step forward and suggest you use Denshield instead of Hardbacker. Denshield offers a protective coating and all that has to be addressed then is the seams and fastener penetrations.:) Denshield is also much much much easier to work with and the fasteners will be easy to "set-the-heads".:)

bigphil 09-29-2011 12:13 PM

Thank you both for the replies. I'm in Seattle btw. well...I already purchased the hardiebacker and my buddy had a bag of r15 yellow fiberglass batts (freebie) that fit perfect so thats what I used. I suppose I'll just keep the paper on the insulation then because I already have some cbu up there and its a pain to take it down. I'll be sure to apply the RedGard properly to be sure its 100% waterproof (i'll probably throw 3 layers on instead of two). thanks again!

Bud Cline 09-29-2011 01:02 PM

Hardibacker will easily require a minimum of three applications.:)

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