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Unread 11-22-2020, 06:58 PM   #2
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Join Date: Jul 2001
Location: Boerne, Texas
Posts: 92,793
Welcome back, Joe.

A link to the shower receptor you intend to use would be a good first step to getting us all on the same page.

While James Hardie is the only manufacturer of CBUs I'm aware of who indicates his 1/4" product as a tile backer for walls over maximum 16" stud spacing, I would not recommend your planned method. I think you'd do much better shimming your studs and installing the thicker Hardiebacker 500 (which is not a full half inch thick. Wood shims of an appropriate thickness (I much prefer rips of plywood for such furring) would allow you to install your CBU with its face flush with your existing walls if that's what you want and would satisfy the Hardiebacker installation requirements. Or you could use an actual CBU (ASTM C1325) that is actually 1/2" thick if you prefer.

In any case you must either install a polyethylene sheet behind your backerboard and draped over the tiling flange of your receptor or a direct bonded waterproofing membrane over the entire face of your backerboard. But not both.

I would also recommend you increase the height of your waterproofed wallboard to a couple inches above where the pipe comes out of the wall for your shower head.

My opinion; worth price charged.

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