Do we need to put plastic vapor barrier behind durock cement board ?

[Curiousv]

I am confused do we put plastic vapor barrier - if we are using durock edgegarud cement board?
and regard and kerdi membrane both on top of cement board i.e between cement board and thinset/tiles?

Also wondering can we use both redgard and kerdi membrae as have some extra?
if not ...what would you choose between redgard and kerdi?

 

[wwhitney]

You want exactly one vapor barrier layer on your wall. So if you are using a surface applied waterproofing (which would also be a vapor barrier), you don't put any vapor barrier behind your cement board. That also means that if you have fiberglass batts in the stud bay behind the cement board, you use unfaced batts.

Have you considered using a foam board with a waterproof face where you only need to treat the joints and fastener locations? E.g. Kerdiboard and Kerdiband, or Goboard and their sealant, etc.

Cheers, Wayne

 

[Sponsor]

 

[Curiousv]

You want exactly one vapor barrier layer on your wall. So if you are using a surface applied waterproofing (which would also be a vapor barrier), you don't put any vapor barrier behind your cement board. That also means that if you have fiberglass batts in the stud bay behind the cement board, you use unfaced batts.

Have you considered using a foam board with a waterproof face where you only need to treat the joints and fastener locations? E.g. Kerdiboard and Kerdiband, or Goboard and their sealant, etc.

Cheers, Wayne

I am more confused..now this bathtub/bathroom has one exterior wall and 2 interior wall ..
On the exterior wall there is fiberglass insulation which has brown paper on it ..(so thats faced batt correct?)
so on this wall when we put durock cement board - we dont put redgard or kerdi memberane and neither plastic vapor barrier?
because that brown part (face) will take care of it?

 

[wwhitney]

No, brown paper batt facing is not waterproofing. So you need the Kerdi or redgard on the inside of the cement board as waterproofing.

But since that waterproofing is also a vapor barrier, and you don't want two vapor barriers in the same wall assembly, you also need to replace the face batts in the exterior wall with unfaced batts. You may be able to just peel the facing off the batts. And you certainly don't want to add plastic behind the waterproofed cement board.

Cheers, Wayne

 

[Curiousv]

No, brown paper batt facing is not waterproofing. So you need the Kerdi or redgard on the inside of the cement board as waterproofing.

But since that waterproofing is also a vapor barrier, and you don't want two vapor barriers in the same wall assembly, you also need to replace the face batts in the exterior wall with unfaced batts. You may be able to just peel the facing off the batts. And you certainly don't want to add plastic behind the waterproofed cement board.

Cheers, Wayne

Ok I can remove the brown paper and it will make them unfaced batts
no plastic behind the waterproof cement board.
and when I am waterproofing front of the cement board - no waterproofing/vapor barrier behind the cement board.
All above is final ? I am attaching screenshot I got from Kohler/sterling bathtub manual that I have ..
to my understanding thin part towards the front (close to u when u r sitting in it) is tile wall than comes the cement board(dimpled one in pic) and than comes furring strip to make up for the tub flange lip with studs..correct me if am wrong in to anything.
Also 1/8" silion goes between tub deck and tile+wall board ..basically we set wallboard just 1/8" above tub deck and same with tile wall and fill this 1/8" gap with silicone?

 

[wwhitney]

Yes and yes.

Typically for the silicone you'd use a caulk that is color matched to the grout you are using, most grout manufacturers offer that.

Wayne

 

[Curiousv]

Yes and yes.

Typically for the silicone you'd use a caulk that is color matched to the grout you are using, most grout manufacturers offer that.

Wayne

Just confirming last thing ..both tile and cement board will sit 1/8" above the tuck deck correct? and that area to be filled with silicone?

 

[wwhitney]

That would be in accordance with the diagram, although you don't fill the area, you install a bead as shown. I don't have a strong opinion on the gap height of the cement board above the deck.

Cheers, Wayne

 

[Jadnashua]

Rather than tear off the paper face, it is acceptable to take a razor knife and put some slashes through it. THe idea is you don't want to trap moisture in between multiple barriers. WIthout the paper, the insulation may slump down, leaving gaps at the top.

My personal preference is to use a surface waterproofing material, and while some prefer a paint on one like RedGard, I like a sheet membrane like Kerdi. It's harder to get a proper waterproof layer with a painted on one without pinholes, runs, or thin sections. Too thick is just as bad as too thin, whereas, with a sheet, you need to ensure the seams are done right, and with the required minimum overlap, there's extra protection there. Normal cement board is not waterproof. One of the foam-core panels work, too, but there you have seams and screw holes to waterproof. Not hard, but required in their systems.

 

[Curiousv]

Rather than tear off the paper face, it is acceptable to take a razor knife and put some slashes through it. THe idea is you don't want to trap moisture in between multiple barriers. WIthout the paper, the insulation may slump down, leaving gaps at the top.

My personal preference is to use a surface waterproofing material, and while some prefer a paint on one like RedGard, I like a sheet membrane like Kerdi. It's harder to get a proper waterproof layer with a painted on one without pinholes, runs, or thin sections. Too thick is just as bad as too thin, whereas, with a sheet, you need to ensure the seams are done right, and with the required minimum overlap, there's extra protection there. Normal cement board is not waterproof. One of the foam-core panels work, too, but there you have seams and screw holes to waterproof. Not hard, but required in their systems.

So if we use foam-core boards ..we dont need to use redgard or kerdi etc waterproofing layer correct? only waterproof on holes and seams ?
Now I have second thoughts about tiles ...what are my options - I could use surround wall but there is a window in exterior wall and I can not cut that big hole in surround wall either acrylic or fiberglass ...

 

[Jadnashua]

Boards like KerdiBoard or WediBoard are totally waterproof once you've dealt with the seams and fastener penetrations. You'd neither need nor want any additional waterproofing/vapor control layers. There are a couple of other makers, but KerdiBoard and WediBoard have MUCH more history and use around the world so have the kinks worked out.

Schluter has a bunch of videos on their website that show how to use it. Here's a general one on some of the capabilities.

Go to www.schluter.com and watch a few of their videos to get an idea how this type of board is used and the possibilities. Here's a long video showing building a Wedi shower.

FWIW, while you could deal with the seams in KeridBoard the same way as on Wedi, the sealant is way more expensive than thinset and the small amount of KerdiBand you'd use. They both work, assuming you follow instructions have have decent workmanship.