Basement shower build question

[Aw2]

Hello everyone. I have enjoyed this forum for a long time and appreciate all of the helpful and knowledgeable people who take time to post.
With that said, i have a question. I am finishing my basement. I have rough in plumbing for the bathroom and plan to build a walk in shower. Due to the layout of the plumbing, one wall of the shower would be against the foundation (8" poured concrete, 9' high). Originally I felt i had a solid plan, but I'm becoming a bit concerned about a couple items.
So, the shower will be approx 42x60. The 42" wall will be against The foundation. I have no water seepage in the wall, it is unground to about 12" from the sill, sprayed from the outside with thick tar and insulation, tough n dry sustem.
My plan was to apply 2" ridgid xps foam to the foundation wall, seal with expanding foam at all seams and tape, then frame a standard 2x4 wall with unfaced fiberglass or roxul. Wall covering will be mold/mildew drywall for a Kerdi shower system.
My concern is placing the kerdi system inside the shower and then having a permiable space with the stud wall, followed by the thick risgid foam. I don't want to create a safe haven for mold growth. I am going to attach a rough sketch of the planned layout for reference.
My question is does this sound like a solid layout? Or one that will lead to moisture problems later. Is there a better way to handle this foundation wall? I can't apply anything directly to it as it is a brick pattern.
Thank you for any and all of your opinions. I truly appreciate it.

 

[Jadnashua]

IMHO, you could forego the framed wall unless you need the space for plumbing, and apply the Kerdi directly to the foam (assuming it is dense enough). Essentially, their KerdiBoard and their foam pan and curbs are all extruded, high density polystyrene, and work just fine covered with Kerdi applied with thinset. ANd, I would not use the moisture resistant drywall...if you use drywall there, I'd use the 'plain' stuff. The moisture resistant stuff, at least some of them, is slightly waxy, and would compromise the thinset bond.

Or, you could use 2" KerdiBoard directly on the foundation wall to provide the desired insulation, and be ready to tile once you sealed the seams. Use gobs of thinset and you can plumb the wall at the same time in the process. Schluter shows doing this (with thinner panels) in one of their how-to videos.

 

[Sponsor]

 

[Aw2]

IMHO, you could forego the framed wall unless you need the space for plumbing, and apply the Kerdi directly to the foam (assuming it is dense enough). Essentially, their KerdiBoard and their foam pan and curbs are all extruded, high density polystyrene, and work just fine covered with Kerdi applied with thinset. ANd, I would not use the moisture resistant drywall...if you use drywall there, I'd use the 'plain' stuff. The moisture resistant stuff, at least some of them, is slightly waxy, and would compromise the thinset bond.

Or, you could use 2" KerdiBoard directly on the foundation wall to provide the desired insulation, and be ready to tile once you sealed the seams. Use gobs of thinset and you can plumb the wall at the same time in the process. Schluter shows doing this (with thinner panels) in one of their how-to videos.

I never thought of using the kerdi board panel as the backer against the foundation wall. I guess what concerns me most is making a waterproof sandwich with the construction.
Would i need to grind/rough up the foundation wall prior to application of the thinset to ensure a strong enough bond?
Great tip on the drywall too, I didn't know about the waxy finish.

 

[Jadnashua]

If the concrete foundation wall is not painted or sealed, regular thinset will hold KerdiBoard to it just fine. KerdiBoard has no organic materials that would support mold growth. IF the wall was clean before you install the panel, I don't think it would be an issue. Do you get moisture through the foundation now or if it does get wet, is it from condensation? If condensation, and no moisture from outside, the additional insulation and blocking air movement should prevent that from occurring.

Schluter's tech support line is pretty good...check that out and watch the video they have on their site where they apply KerdiBoard to a concrete wall. You'll want a long level, but with the thicker panels, it would be hard to bend them, so a shorter one would probably work.

 

[ting tu]

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