Kerdi over Red Guard? [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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08-14-2009, 05:43 PM
New poster rady to remove a fiberglass shower unit and go in with a tile over KERDI system. I am ripping out a fiberglass unit thats 60"*34". Along one 60" side the wall was framed and hardi board was installed, and coated with red guard waterproofing paint on membrane. Should I demo the hardi board, or can I install the KERDI over the red guard, looking for some expert opinions. This is a trial run in the guest bathroom so I can do a better job in the master bathroom, but this being my house and one I intend to die in eventually, I would prefer to do the job once right, and never ever have to think about it again. Another question, is there any documentation of how the system has held up in earthquakes, I know my house does some serious swaying in moderate shakes and wonder will the KERDI have any defects from that movement that would not be evident under the tile?

Thanks, once I start, I'm sure I'll have lots of questions, but the finished projects I've seen posted are stunning!!!

Take Care,
Don trousdale

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08-14-2009, 06:00 PM
Welcome, Don. :)

First you gotta be really sure it's RedGard you're lookin' at, there, eh?

No doubt in my mind that you can install Kerdi over Redgard over CBU. RedGard is a direct-bond waterproofing membrane, just as is Kerdi. Dry-set mortar will stick quite nicely to either. Or both. But if you do that, won't nobody be your friend.

Schluter will say RedGard is not a recommended backing for Kerdi.

Custom will say RedGard wasn't designed to have a sheet membrane bonded over it.

Thinset mortar manufacturer will just scratch its collective head and wonder why everyone can't agree on what type of mortar to use with their various waterproofing membranes.

All will say, "Don, who?" :scratch:

But you can do it if you wanna. If your walls are not really flat, and really plumb, and really square, though, I'd tear it out, fix the framing, and install sheetrock per Schluter's requirements.

Don't know if they got any earthquake data. But the shower sheetrock covered with Kerdi will fare better than any of the other sheetrock in the building. If that's of any consolation to ya. :)

My opinion; worth price charged.