Underlayment Stone Floor with Radiant [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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02-16-2010, 03:14 PM
Well I've read at least a dozen posts about underlayment for stone and I understand that the recommendation here for natural stone is two layers of plywood. I am trying to reconcile that with the installation recommendations for Ditra with radiant floor heating which show one layer of plywood. Full disclosure, I'm remodeling my master bath - second story, I joists 16 inches on center, 3/4 inch plywood. There was previously 12 inch porcelain tile thinset directly onto plywood (I know many of you are having heart palpitations, but there was no cracking in the 10 year old home, so clearly the floor is pretty stiff). I'm planning on installing 18 inch travertine and an electric radiant system with Ditra - based on Ditra installation instructions:

Latex mortar/Mat/thinset/Ditra/thinset/tile - all shown over ONE layer of plywood if your joists are less than 24" with stone (D-RE-08)

I am dealing with a junction to carpet, so want to keep layers to a minimum. Can I proceed with recommendation - or am I asking for trouble?

Thanks so much for all the good advice!!!


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02-16-2010, 03:23 PM
Debbie, in the fine print, the D-RE-09 refers you to a number of subfloor details, one of which is DW-S-09. That one is the double wood subfloor for stone installations.

Even if it didn't, I wouldn't recommend a single subfloor; radiant heat and travertine. There's too much to loose.

02-16-2010, 04:23 PM
Fine print - rrrrr - thank you for the heads up - so if I had 1/2 additional ply layer - the rest of the instructions are good to go? Realistically what's the total depth I'm looking at? FYI the tiles are about 1/2 inch.

02-17-2010, 05:29 AM
Heat mats are usually about 1/8" thick. Ditra is 1/8" thick. You may have to allow about 1/4" for your thinset. 1/2" tile and 1/2" plywood, that's about 1-1/2".

You can install carpet shims (http://www.carpetshims.com/) (ramps) under the carpet to ease the transition.