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nan0
12-06-2005, 02:04 PM
Hi guys and gals-

quick question from a DIYer - I'm installing insulation behind the shower Durock walls,more for sound damping than temp control. The insulation I bought is wrapped completely in plastic (front, back, sides) and says it can be installed to double as a vapor barrier as well. I know not to install another vapor barrier over the insulation, but should I do so in areas where insulation won't fit or where I've needed to trim the insulation to make it fit?

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Rd Tile
12-06-2005, 04:40 PM
I always get confused on insulation, kraft faced, unfaced, faced, foil wrapped, this side out and thins side in, but I will say, it won't work as a vapor barrier behind a shower wall, you need to cover the studs between the wall and backerboard 100%, unless there are lips on the insulation thet overlap each piece in the stud bays by 2" or more.:)

Tool Guy - Kg
12-06-2005, 10:21 PM
nan0,
I'd want the moisture barrier behind the cement board to overlap onto the tub's flange. You aren't going to get that with the bagged insulation. I'd install all the insulation in the bag, then cut a bunch of slits in the insulation's plastic once it's up. Then install plastic over the entire wall and overlap the bottom of the plastic over the tub's flange. The slits will allow any moisture that finds its way between the two to evaporate out. :)

Andrew21
12-07-2005, 11:06 AM
I purchased the R13 insulation (kraft faced) at home depot. Is that ok to install on the inside wall facing out to the exterior? I'm going to use durarock with RedGuard. thanks

Andy

nan0
12-07-2005, 11:45 AM
The insulation claims to work as a vapor barrier as well - there are two flaps on either edge, one for staping to the studs and the other for overlapping those stapled areas. Works fine in theory, then you go and cut the insulation to fit certain locations and your barrier has a hole... I'd read on other forums not to install a vapor barrier over another as it can cause problems if moisture ever gets between the plastics. My next thought was to just put 6mil plastic over those cut areas or areas where insulation wouldn't fit nice.

Will that do, or should I remove the 3 peices of Durock I have up and put plastic over the whole area?

And to expand the question - what is done on the ceiling? Durock, green board? Vapor barrier above it?

DonB
12-07-2005, 02:16 PM
This probably won't answer any questions but all the interior walls in my house are insulated with kraft faced 3" stuff. I tore out a fiberglass shower stall last week and behind it I found studs and insulation, kraft side away.

Don

cx
12-07-2005, 03:55 PM
Welcome, nan0. Give us a first name to call you. Unless that's it. :)

It all gets confusing, no? And part of it is terms and definitions.

What you want, and must have, behind the shower walls is a moisture barrier and drain-plane for any moisture that penetrates the tile, grout, joints, thinset, and CBU. It's not usually much, but you do want it to stop before it contacts the studs or enters the wall cavity, and to have an easy, gravity-fed, route down to the shower pan or tub. Or, in time, to find its way back out the tile wall as vapor.

Depending upon what you use for this barrier, you will have some degree of vapor retarder, but you will not have a vapor barrier with any of it because of the fastener penetrations. If you use something like 6mil poly and seal all of those penetrations, you would have a pretty effective vapor barrier, too, but that's not really what you need most in that application - except when we get into steam showers.

The plastic wrap on that insulation you have is a vapor barrier as far as protecting the insulation inside, but not in your wall, for the reasons you describe. But you do not want and additional barrier behind the one you must have for the shower walls because you want any moisture in the wall cavity to be able to make its way to the exterior.

My recommendation in your case would be to use something other than the insulation batts you have in at least the shower area. But then, I don't like those batts at all. For anything. Bad eye-dee.

My opinion; worth price charged.

nan0
12-07-2005, 05:25 PM
Thanks for the replies.

Names Doug, feel free to call me by that name or any other you conjure up ;)

It sounds like the best solution is what ToolGuy said - cut slits in the insulation plastic and place plastic over the studs, behind the CBU. I need that sound barrier since the shower shares walls with the bedroom.

Means I'll ahve to pull 3 pieces of CBU down, but no big deal.

I've tried attaching some pix, we'll see how that goes...

jadnashua
12-07-2005, 05:32 PM
Note...from what I read, when installing insulation in warm climates, it is not uncommon to install the vapor barrier on the outside wall. They don't want the a/c'ed air on the inside to cause condensation inside the walls by letting that hot moist air in. :topicoff:

Andrew21
12-12-2005, 11:05 PM
Welcome, nan0. Give us a first name to call you. Unless that's it. :)

It all gets confusing, no? And part of it is terms and definitions.

What you want, and must have, behind the shower walls is a moisture barrier and drain-plane for any moisture that penetrates the tile, grout, joints, thinset, and CBU. It's not usually much, but you do want it to stop before it contacts the studs or enters the wall cavity, and to have an easy, gravity-fed, route down to the shower pan or tub. Or, in time, to find its way back out the tile wall as vapor.

Depending upon what you use for this barrier, you will have some degree of vapor retarder, but you will not have a vapor barrier with any of it because of the fastener penetrations. If you use something like 6mil poly and seal all of those penetrations, you would have a pretty effective vapor barrier, too, but that's not really what you need most in that application - except when we get into steam showers.

The plastic wrap on that insulation you have is a vapor barrier as far as protecting the insulation inside, but not in your wall, for the reasons you describe. But you do not want and additional barrier behind the one you must have for the shower walls because you want any moisture in the wall cavity to be able to make its way to the exterior.

My recommendation in your case would be to use something other than the insulation batts you have in at least the shower area. But then, I don't like those batts at all. For anything. Bad eye-dee.

My opinion; worth price charged.


Cx,
So what should I do? I was looking for insulation without the kraft face and couldn't find anything. Should I just install the insulation with the paper/kraft facing away so that the insulation is facing out? I'm planning to use Durarock with Redguard. Just want to see what you think about this. Thanks

Andy

cx
12-12-2005, 11:13 PM
Hang the Kraft-backed stuff, Andy, then cut lots of vertical slits in the paper to defeat the vapor retarding capability. Cut them such that the paper can still support the insulation. Make each one maybe a foot long and stagger them along the face.

Then move right along. :)

My opinion; worth price charged.

Andrew21
12-12-2005, 11:28 PM
Hang the Kraft-backed stuff, Andy, then cut lots of vertical slits in the paper to defeat the vapor retarding capability. Cut them such that the paper can still support the insulation. Make each one maybe a foot long and stagger them along the face.

Then move right along. :)

My opinion; worth price charged.

Thanks CX. .I'll post pics of my project soon. Thanks again

Andy

bljack
12-13-2005, 07:04 AM
Doug, nice job on the pan. I know you have John's book, so no doubt you got a preslope. Just wondering what you have planned for that bench though. That liner will do nothing to protect the wood and the framing if you use cement board on it, once you make swiss cheeses oue of it with your fasteners. Your bench desighn really is a good candidate for a topical waterproofer, painted over the walls from the front of the bench back and then over the bench, up the back wall and extending it past the bench area into the shower are by about 6-8". Can't have a vapor barrier behind some, need one behind others but you are heading down the path of leaky bench syndrome.

Brian

nan0
12-13-2005, 12:10 PM
Brian-

Thanks for the tips, but I've actually mudded up the front, and on top of the bench. No CBU used, except on walls, and definately no fasteners used on that bench! It would have been much safer and easier had I done the liner on the whole thing then built a bench in the shower, but I wanted the area underneath the bench for storage, as we've had to oust other storage areas in leu of a larger shower.

I should have pix off my camera soon (been slacking, and caught a cold).

BTW, when working with cement, cbu, etc, WEAR A MASK! I think my "cold" is partially due to my stupidity in not wearing a mask all the time (it came off after lunch).

And being sick sux.

-Doug

Rd Tile
12-13-2005, 03:41 PM
You would need metal lath for that bench, no?, I would remove the liner, install the liner up the front even with the wall heights, install 3/4" plywood on the top of the bench, covered by 1/4 or 1/2" CBU and 1/2" CBU on the front of it overlapping the liner just like the walls, the mud will hold it at the bottom, no fasteners there, then tape and thinset all the seams, then use Redgard or other paint on waterproofing membrane over the whole bench and up the wall 8 to 10" from it.:)

nan0
12-14-2005, 12:11 PM
RD-

I think I've got everything under control for a leakfree shower bench, here's what I've got -

Bench is constructed of 2x4 frame with 1/2 ply front and side, 3/4 ply top. Felt on top of bench, pre slope on top of that. (see pic 1). liner installed over the whole thing, dam corners in all outward folding edges, no fasteners except for 8" up the wall on all sides and outside edge of curb(see pic 2).

On top of that I put lath up the front and on the top of the seat to provide unfastened support for mudding the front of hte bench. There's about 3/4" -1" of mud on that front surface, the top of the seat and shower floor have closer to 2". I did put cement board on the ouside wall of the shower seat (with the square opening cut in it) to match the 1/2" thickness the outside of my curb will be.

This weekend I'll be installing the last of the cbu (floor of bath) and the drywall around the rest of the walls. Gotta mud the curb and tape the cbu and i think i'll be ready for tile!

Rd Tile
12-14-2005, 02:51 PM
Just curious, how did you mud the face of the wall, make a make shift mold out of wood to hold the mud till it hardened?:)

nan0
12-14-2005, 04:30 PM
:)

you guessed it. Thought i'd be able to just slap the mud up there, but that didn't work too well.