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red86yota 02-19-2009 08:18 PM

help with choosing subfloor for bathroom tile
Hi all,

I've got a new bathroom project and am looking for help on picking the right subfloor system for the job.

The joist system is strong enough for tile (approx L/420, and from what I've read L/360 is min for tile and L/720 for natural stone) The joist spacing is 12". There is already a layer of 3/4" T&G OSB that was glued down using subfloor adhesive and nailed down with 8D nails. We're planning on a radiant floor heater and 12x24" porcelain tiles.

Any suggestions on what to put on top of the OSB? Just some good ol cement board? Does the thickness matter other than trying to match up the height of the tile to the height of the flooring in the adjacent room?

Thanks in advance

JazMan 02-19-2009 09:13 PM

With tiles of that size I would normally say to add more plywood then install Ditra and then the tiles. But because of the 12" o.c. your between-the-joists deflection should be ok. So, go with 1/4" CBU then heat, then make floor flat, then tiles.


red86yota 02-20-2009 06:44 AM

Thanks JazMan..

So you're in Troy, and you're a Kerdi expert? I'm in WB and I'm going to put a Kerdi shower in this bathroom! I may have some questions for you later....I haven't watched the DVD that came with the Kerdi yet.

detroitMi 02-20-2009 08:29 AM

What WB stands for ?

JazMan 02-20-2009 09:06 AM

My first guess is that WB stands for West Bloomfield

You're going to love a Kerdi shower, it's the ONLY way a shower should be built. :thumbup: Are you using the foam tray or doing deck mud floor?


detroitMi 02-20-2009 09:16 AM

Gotcha JazMan,

red86yota 02-20-2009 09:49 AM

Yep, West Bloomfield.

And I'm using the foam tray, plus extending it about a foot on one end.

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