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diy'er on LI 04-27-2012 07:52 PM

a few quick questions about shower cement board and hydro ban
hi all

we FINALLY got our poop together... the plumping is done and our acrylic shower pan is in. So, this weekend, we're putting up the cement board in our shower. a few quick questions:

I'm 90% certain, but just to be sure, I'm supposed to put the cement board a 1/4" above the lip of the shower pan and then fill in the gap with silicone caulking... right? It can't go over the lip because the board would flex a smidge...

the hydro ban instructions are a smidge vague. We put up the cement board, and there will obviously be a seam between 2 boards. Do we use fiberglass tape and skim it with mortar as usual, and THEN use the soaked hydro ban 6" membrane fabric, or do we skip the tape / skim step that is normally done with cement board, and ONLY use the 6" membrane fabric soked in hydro ban over the seam?

lastly, does anyone have some little tips on how to install cement board perfectly plumb in a 35 year old house? a few of the studs are little out of plumb (kinda arched) now. Very subtle, though.

thanks so much for your help :)

JazMan 04-27-2012 10:06 PM

The very best way to handle the flange of the base is to shim out the walls about 1/4" so the board clears the obstruction. Stopping just above the flange also works but you have to make sure to seal that well, and then have faith it'll stay sealed.

Seam the joints with the special fiberglass backer board tape and thinset mortar.

If the studs of not plumb, flat or out of plane, you need to fix that first.

Where did you get the info that you also need HydroBan membrane fabric? Please give us a link or quote.


diy'er on LI 04-27-2012 10:16 PM

Did I ever tell you how much I appreciate your responses to my posts? :)

The membrane fabric thing came directly from the hydro ban instructions from the manufacturers webpage. But now that you mention it, it's only for gaps of I believe 1/4" or more...

I was going to put it on all seems out of super-caution. Probably overkill.

It probably should be put in the corners, though... especially around my shower bench. so I don't need it on flat seams, I guess.

How do I fix those subtle out of plumb studs? The wall in question is not load bearing... Should I plane it down?
(Mercifully, the one load bearing wall is perfect as far as I can tell.)

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