03:29PM | 06/27/07
Member Since: 06/26/07
2 lifetime posts
I see a variety of answers to how thick the subfloor must be prior to laying tile. What's the bottom line.

In my case, I have a kitchen floor I would like to tile -- probably with 16" porcelain, but could go 12" if needed. The joists are 2X8 Doug Fir 16" OC, 10'2" unsuported span.

The current floor is 1/2" plywood with 3/8" particle board on top. Everything is in sound condition.

My intention was to float the surface for tile installation or, I could go Ditra, or whatever is a good choice -- but not go cost crazy.

How should I prep the sub floor. It what I have adequate? Should I add 3/8" or 1/4 inch plywood on top of the existing particle board and ply and screw it all into the joists? Should I rip out the particle board and put in 5/8" plywood? What will work, and what would be best?

Thanks for any help -- Rodger

doug seibert

05:28PM | 06/27/07
Member Since: 08/10/02
842 lifetime posts
The John Bridge Forum has a DEFLECTO calculator that checks the soundness of your structure

The large tiles require a stout floor.....Check the some articles in the "Liberry".....register and chat in the forum

"...measure once.....cut twice....throw that one away and cut a new one...."


04:55AM | 07/01/07
Member Since: 07/03/05
283 lifetime posts
rip out the particle board, it has no place being under a tile installation. Put 1/2" underlayment rated plywood, like ACX or BCX,perpindicular to the existing one half inch ply. Leave a 1/8" gap in the seams and fill with cheap latex caulk, use screws at 8" intervals, dont worry about hitting the joist with the screws. Put Ditra or cement board over that. Check the Deflecto to see if you need midspan supports for your 2x8s.


04:40PM | 07/01/07
Member Since: 06/26/07
2 lifetime posts
Why the 1/8" gap and caulk -- expansion?



10:15AM | 07/04/07
Member Since: 07/03/05
283 lifetime posts
Yes, wood expansion must be honored. The caulk keeps the thinset from filling in the gap, which would defeat the purpose of the gap.
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