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Unread 02-07-2014, 06:00 PM   #1
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Join Date: Sep 2013
Posts: 16
Slate floor underlayment help

Hello all,

I've posted here before, and you were very kind to give me advice regarding my botched shower job. Someday it will be fixed, I hope.

Until then, I've decided to work on a different room. I want to install slate in a teeny powder room. Myself. It's a 5' x 6' room. I've chipped away the marble mosaic that was there to find the original porcelain mosaic peeking through a very thin layer mortar/thinset. The tile itself is visible in large sections of the small floor.

The original porcelain mosaic is 100+ years old and set in what looks to be a very sand-heavy mud (?). You can see the mud by looking up through the floor boards of my basement. It's a very coarse sand mix.

Can I tile over this? The floor is out of level only to the extent that the thinset from the marble remains. Won't the thicker mortar bed I need to use for slate "compensate" for the slight roughness of the old thinset? I don't see any cracks in the floor or tile, though there are holes from where the radiator used to be.

Would you recommend a decoupling membrane in this situation? The powder room is on the first floor of a wood framed house, above the basement. The POWDER ROOM hangs a bit lower than the floor joists because it's under the stairs (there's a step down).

Thank you

Last edited by Stefanie3434; 02-07-2014 at 06:02 PM. Reason: I used the wrong word and didn't catch pre-post
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