Flooring Tile - Tiling advice on room that is half concrete half plywood

Hi folks, need some good advice here. The Foyer of my new house is partly on concrete slab and partly on plywood, the plywood portion being the space over the basement.

I'm concerned about have 2 different subsurfaces for the tile to contend with. I'm worried it will crack since each half of the room will respond differently to moisture and possibly wear.

Has anyone had to deal with this before? Thanks for the help!

P.S. I just read that I can't use concrete backboard over the concrete slab. Ack, I'm lost. Should I just give up on tile and use a floating hardwood install?

If the plywood and slab are on the same plane use a membrane like ditra for both the ply and slab. You need to do your layout so that a grout line will be directly over the joint where the two floors meet. Dont grout that that joint, use a color matched caulk. The caulk will compensate for the different rates of movement between the two materials. All grout manufacturers make color matched caulks for each of their grout colors. The caulks come in sanded and non sanded to match the texture of the grout.

Thanks Johnny,

Seems that might work. Interesting that the tile orientation is pretty much predetermined so no diagonal tile options.

Also a little worried about subfloor adherement. Tile on concrete slab isn't a problem but I would need to put the tile directly on the plywood to maintain height. Or I could build up the plywood with backboard but then what would I use to build up the concrete section? ARGH!

Use an uncoulpling membrane like Schluter Ditra or Noble CIS over both the slab and the plywood. This will keep them at the same height. Im most familiar with Ditra. Use an unmodified thinset to bond ditra to the slab, and a modified thinset to bond ditra to the plywood. Use good quality thinsets, dont buy the cheapo stuff for this. You can then set your tile with a good quality unmodified thinset over the ditra. If you go to the Schluter website, theres lot of info on ditra, including a handbook/installation guide. They also have great tech support and will answer any and all questions you may have about their products.

Without seeing the space your working with, Im thinking yes your limited as to tile orientation. You do have to honor that joint where the slab and the ply meet.

Thanks again Johnny, I will definitely do that.

I got a reply from the builder about the subfloor. They said they will use gypcrete subflooring over the basement area. But they said nothing about the seam issue.

Will gypcrete that care of that? I'm thinking no but would like to hear your opinion.

What you should know about gypcrete. Dont tile directly over it. It cracks and crumbles over time. I have seen lots of this stuff used in condos and Im not a big fan of it. You need to use an isolation membrane over it.