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Dshamgar 12-28-2011 05:54 PM

How to seal below concrete board sealed with RedGard

I am remodeling my bathroom. I will be installing ceramic tiles in the shower stall walls, and using an Onyx shower base. I have already installed concrete board (HardiBacker) onto the studs, and plan to waterproof it with RedGard.

My question is this: since there is a 1/4" gap between the bottom of the concrete board and the lip of the shower pan, what should be done to waterproof that gap? I understand that there will be mortar there in back of the overhanging tiles, but I am concerned about water getting through the tiles and mortar.

Any advice is appreciated!


Bud Cline 12-28-2011 06:00 PM


abracaboom 12-28-2011 06:07 PM

That 1/4" gap is to keep the cement board from wicking up moisture. When you tile, spread your thin-set mortar all the way down, but set your tiles up a bit using spacers. When the mortar is cured, run a small bead of silicone to seal between the tub and the tiles.

Bud Cline 12-28-2011 06:15 PM

DO NOT use thinset in that gap.

Caulk that gap with siliconized or latex caulk and then use Redgard over the caulk. Regard will not stick to 100% silicone caulk. You DO NOT want moisture collecting in that crevice and it can if you stuff it with thinset.

Then after the tile is installed caulk that gap also. I wouldn't ramp those tiles either. There is no need for that and that would look really stupid. No reason to have those two or three tiles tilted/ramped.

shorteared 08-14-2012 09:18 AM

Hello Bud,

I know this thread is old but i hope you can reply to it.

Can I use an Acrylic latex caulk plus silicone in this same situation posted earlier or does it have to be straight latex?

Hope you can still reply to this thread

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