Hello Everyone,

New to the forum and had a couple of questions about the proper method for tiling over my subfloor.

I have a 100 year old farmhouse with (real) 2"x10" floor joists on 16" centers. The area that I am tiling is a bathroom on the second floor and the maximum span for the joists is 11'6". In the area where the bathtub and shower are I have doubled the floor joist's and added cribbing to the entire floor. The subfloor is 3/4" T&G pine of varying widths (2 1/2" - 5") that is in good shape. I have screwed the subfloor down with 2 1/2" deck screws and then put down floor leveler. There is a low spot in the middle of the room that is 1/2" lower that at the edges. I have also installed radiant floor on the underside of the sufloor with metal reflectors.

Now for the part I am unsure about. I was told that the 3/4" subfloor would be fine with floor leveler, thinset, 1/8" Ditra, thinset ,3/8" marble tile; in that order. The only thing is I am now reading here that I maybe should have beef'd up the subfloor. If this is so what do I need for sheeting 1/4", 1/2" ply? 1/4" Hardibacker? Can I lay the sheeting down directly on the floor leveler or do I have to take the floor leveler up (hope not) and install the sheeting first then relevel the floor?

Any help would be very much appreciated,

Thanks,

Satflier

You definitely need a layer of plywood on top. 3/8" would be the minimum, 1/2" would be better. Don't use Hardibacker to stiffen the floor, it's not meant for that.

Unfortunately, I don't know of any way to properly secure the plywood without removing the self leveling compound you have. Someone else might have an idea.

Regardless, this article has info about the proper way to screw the plywood down.

http://www.schluter.com/5138.aspx

No manufacturer of self leveling cement would allow it to be poured over 3/4" 1 by plank flooring. Who's product did you use?

Unfortunately Kman is right about removing the self leveler. You need a layer of plywood attached directly to the plank floor boards only.

Remember, your installing a natural stone tile, the subfloor/joist requirements are much more stringent. If you have sistered joists to all of the tiled areas then your floor structure is one step closer to successfully installing natural stone, but you still need to meet Schluter's requirements for installing Ditra.

Randall/Kman,

Sorry for not responding sooner. I removed the leveling compound (a $200 lesson) and put down 1/2" ply then primed and redid the leveling compound (Super EZ Flow). I now have the ditra laid and am ready for tile.

Thanks for your help,

Satflier

You'll be glad you did it correctly.