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Discussion Starter · #1 ·
Hi. I'm new here, and looking for some feedback.

I live in Southwest Florida. I have a 1965 block ranch. We had an issue with mold in a wall that abutts the shower, and I demo'd the whole bathroom. I'm putting it back together, with a tub, and plan to install a tile shower surround. One of the primary walls is an exterior block wall.

I plan to use straight EPS, unbacked foam (like styrofoam coffee cups stuff) between the furring strips, and I want to make sure to install a waterproof, relatively highly permeable material behind my hardieboard, so the wall can breathe, but still keep water at bay. I want to use tar paper with a water & ice membrane around the tub flange, and hardie over that, with taped and thinset seams, but I'm concerned about the stink from the tar paper.

I'm considering using Kerdi wrap instead of the tar paper, but I'm not sure it will give me the permeability I want.

I'm looking for someone to either A) say that the tar paper won't smell at all, or B) say that the Kerdi is plenty permeable for the wall to breathe.

Holler with thoughts? Thanks!
 

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There's no need for it and it would just form a double vapor barrier..
Any waterproofing (in effect vapor barrier) is done over the face of the tile board before the tile goes on.
 

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Discussion Starter · #3 ·
Thanks for the reply Joe!

Hmm... there's no need for what? Either? As I understand it, grout and cement board are porous, so theory is that water would get behind them. Kerdi does go over the Hardie, if I choose that route. Are you suggesting that I use the Kerdi, and not the tar paper? Does Kerdi offer enough of a permeability in case any water does get behind?

I believe there is a distinct difference between waterproof, water retardant, vapor barrier and vapor retarder. I like the idea of the felt because it's very permeable and will absorb the water to let it dry out...
 

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The Kerdi or a product like Red Guard is all you need to stop the water from getting in behind the wall.
 

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Discussion Starter · #5 ·
I am confident that the Kerdi will stop the water. I'm mainly wondering if it's permeable enough to be on that layer of my shower wall. I understand it's perm rating is 0.75 (http://www.diytileguy.com/shower-waterproofing-and-vapor-barriers/). Being in Florida, where we are, with block walls and my only known vapor barrier on the outside being nothing more than latex paint (aka, not a vapor barrier), I don't want to have the outside moisture (water vapor) coming through the wall, as it's going to do, and hit the backside of something (like the Kerdi) and not be able to get through, thus getting stuck at the hardieboard level...

Mind you, I don't think there is a ton to worry about here as I have a terrazzo over slab floor, and only the furring strips are wood, and they're pressure treated.

I think if the Kerdi is a vapor retarder (not a barrier), then I may have just talked myself into using it - over the hardieboard
 
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