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joe14580 11-22-2020 06:02 PM

Shower walls are a somewhat odd thickness
Hi guys,

My brother and I are remodeling his bathroom, replacing the 5' tub with a 5' Sterling shower pan. We ripped out the existing drywall on 3 walls to about a height of 78" so we could install Hardie Backer from the new shower pan to the existing drywall. The Hardie backer will butt up with against the existing drywall at a height above where the water will exit the shower head.

The existing walls throughout the entire house are 7/8" thick, consisting of 1/4 " drywall nailed to studs and topped with 5/8" drywall.

I was going to replace with 5/8" drywall topped with 1/4" Hardiebacker to achieve the desired 7/8" thickness. I was not going to put any thinset between the Hardiebacker and the 5/8" drywall, just screw the hell out of the underlying 5/8" drywall into the studs and screw the Hardiebacker every 8" through the 5/8" drywall and into the studs.

If this is ok, I'll tape the Hardiebacker seems with tape and thinset. Should I also Redgard the Hardie Backer seams to insure no moisture reaches the underlying 5/8" drywall ?

Alternative would be 1/2" drywall with 1/4 hardiebacker on top and 1/8 " of thinset between them, but I think it would be difficult to achieve 1/8" thinset consistency (we're amateurs).

Thoughts please ? :confused:


cx 11-22-2020 06:58 PM

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.

Tool Guy - Kg 11-22-2020 07:00 PM

I’d rather simply rip some 1.5” wide strips of wood to exactly the correct thickness for whichever 1/2” backer board you wanted to equal your wall thickness. I personally don’t enjoy the way Hardiebacker is sooooooooo thirsty that it needs multiple wipes with a damp sponge before the mortar is spread. But I’ve used it countless times.


joe14580 11-22-2020 09:36 PM

Cx and Tool guy,

Thanks for your responses.

I apologize but I don't know what a shower receptor is ?! The existing tub is installed in a 60" x 30" wall pocket, we'll be replacing that with a Sterling shower pan and tiling up to the shower head. BTW, studs are 16" spaced.

What CBU do you guys like ? We have HD and Lowes available to us plus some other local stores. Which CBU is a true 1/2 " ? Is Redgard a suitable water proofing membrane ?



Tool Guy - Kg 11-22-2020 09:47 PM

Receptor = your Sterling shower pan.

I personally like true cement boards like Durock. It is a bit less than 1/2”. Permabase is another true cement board.

And RedGard is a perfectly fine waterproofing membrane.


joe14580 11-23-2020 07:04 AM


Thanks, I know I can get Durock and will use that in lieu of Hardiebacker.

Tool Guy - Kg 11-23-2020 10:19 PM

All other things being equal, it’s easier to get a wicked-strong bond to Durock. The only downside is that it’s a little messier when cutting. But that’s easy enough to clean with a vac.


joe14580 12-09-2020 05:29 PM


Yup, I returned the Hardie and bought Durock. Thanks.

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