Kerdi over Plaster [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-24-2008, 06:58 PM
I have a bathroom I am going to tile and was wondering if I use thinset to level the plaster can I put Kerdi over it? I figure if I wet the scratch coat on the missing spots so it doesn't suck the water out of the thinset I can skim it.

This is the back wall of the shower. I would like to do the side wall also but I don't know if that's a good idea. The wall with the mixing valve is cement board.

I was wondering what the best way to raise a floor flange under the toilet if I tile over the existing tile. The tile now is a mud floor so it is rock solid.

Thanks, Jeremy

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02-24-2008, 07:46 PM
Hi Jeremy. Yes, thinset will stick to plaster then you go go over the thinset with more thinset and Kerdi.

02-24-2008, 08:38 PM
Thanks Davy, Should I wet the plaster first so it doesn't suck out the moisture.

02-24-2008, 08:41 PM
You can, won't hurt anything. Thinset will fill voids up to about 1/4 inch thick at one time. Not sure how deep your patches are. :)

02-24-2008, 08:46 PM
Is this ok for the side wall too? Any idea for the floor flange? I figure I can mount a repair flange over the old flange to raise it up and use a wax ring with a horn.

Tool Guy - Kg
02-24-2008, 08:57 PM
You can use Kerdi over the side wall that has cement board, as well. In fact, without a moisture barrier behind the walls, it would be wise to use the Kerdi for all 3 walls.

As for the closet flange, buy an extender ring(s) like the ones pictured below and use 100% silicone to seal it to the original closet flange. Make sure the old flange is cleaned of wax before sealing the new one down. :)

02-24-2008, 09:02 PM
Thanks Tool Guy. The side wall currently has plaster on it. If I need to do cement board I will. The only wall with cement board is the front wall with the shower valve in it.
Thanks again for both of your help.

02-24-2008, 09:12 PM
Hi Jeremy,You can leave the plaster as planned.The reason there's a cement board on the pipe wall is there must've been a problem with leaking.So since you're using Kerdi,keep the walls you have.

02-24-2008, 09:45 PM
Thanks Micheal, ALL you guys saved me alot of work. Thanks again to all that helped.

02-24-2008, 09:58 PM
For Kerdi they say unmodified thinset. I use Versa-bond for normal tiling but that is fortified. Would you recommend Custom blend for Kerdi or is there a better thinset for Kerdi. Thanks