Replies

1. 
   user-2310254 | Jul 28, 2017 10:34am | #1

   Howard,

   I would install a waterproof membrane such as Schluter-Kerdi over the cement panel. The system is pretty straightforward.

2. 
   user-3368124 | Jul 28, 2017 06:06pm | #2

   Thank you - to be clear, from OSB side
   OSB - Schulter membrane - Cement board - tile ??
   Thx, Howard

3. 
   fourforhome | Jul 28, 2017 09:16pm | #3

   Howard, I have a tiled shower against a SIP wall and the cement board goes against the SIP and then the Schluter membrane, then tile. (OSB - cement - membrane - tile) Just remember that the SIP osb doesn't have the same holding strength as a stud. Be generous with the screws.
   Durock also has a membrane/shower system that seems to cost a bit less than Schluter.
   (http://www.homedepot.com/p/DUROCK-48-in-x-48-in-Shower-Kit-with-Center-Drain-170132/205339085)

4. 
   user-2310254 | Jul 29, 2017 08:31am | #4

   As Mark indicated, the waterproof membrane is installed over the cement board. You could also use a fluid-applied system such as Redguard.

5. 
   ohioandy | Jul 29, 2017 09:39am | #5

   Even better, Schluter makes it very clear that their membrane system can be installed over standard drywall--it doesn't have to be moisture resistant, let alone cement board. I often use 1/2" Fiberock, a gypsum product which seems to have more stiffness than drywall, and can extend past the Schluter membrane and be painted like drywall. Using actual cement board with Schluter is way overkill, too much work, and shows that you don't trust the membrane system.

   To your question about airspace behind shower wall, several years ago on this forum someone suggested putting thin lath strips between the drywall and the OSB SIP skin, just to create a vapor-open assembly that will mitigate against unforeseen (or unseen) water damage. It's the ol' belt-and-suspenders.

6. Expert Member
   MALCOLM TAYLOR | Jul 29, 2017 10:35am | #6

   Howard,

   The location of the membrane depends on what system you decide to use build the shower.

   Schluter depends on the membrane as its waterproofing and you tile directly onto it, so you can use a variety of backers including regular and coated gypsum board, and cement based substrates.

   Coated gypsum-based substrates like Dense-shield are also both the waterproofing and tile-backer, so if you were going to include a membrane as further insurance it would go behind the Dense-shield.

   It is also common to use cement board as a tile substrate, and the membrane would go behind it too.

   In each case it is important to integrate the bottom of the membrane into the shower pan or drainage.

7. Expert Member
   MALCOLM TAYLOR | Jul 29, 2017 05:54pm | #7

   Steve,
   No, not with Schluter. I was listing three options most people use.

   The most common shower assembly is still probably cement board over a vapour barrier or building paper. I'd substitute a membrane like Grace I&W for the VB if it was going directly onto the OSB SIPs skin.

   As you say DensShield is weak at the seams, so a membrane as a backer behind it in these circumstances is a good idea too.

   Edit: I don't see much point in using a cement board behind a Shluter membrane. It's virtues are negated by being behind the waterproofing. I'd use something that held screws better and was easier to work with like green board - or DensShield.

8. 
   user-3368124 | Jul 30, 2017 05:37am | #8

   Thank you for the feedback. My biggest concern is the air space / membrane. I can pull a design from these comments, thanks. H

9. 
   user-2310254 | Jul 30, 2017 09:49am | #9

   Malcolm,

   I did not see an option for placing the backing material in front of the Schluter membrane or panel. If you were using the panel, I suppose it could be applied to the studs. But I would advise Howard to check with the company's support line for further guidance.

   DensShield is a backer plus moisture barrier product, but I think you must be careful about sealing all penetrations (which is the case with Schulter as well).