I should have been more specific. He said that if we float it with only thinset it could crack due to the height needed.

A. cant correctly answer w/o knowing the current Substrate.

B. Thinset should not be used w 12x24 tiles youll need a quality medium bed mortar.

C. If its a bondable slab id probobly Wet set these tiles and flush out to hardwood.

D. If its a plywood subfloor w levelker already poured id ask you what the deflection rating is before answering.

This is his incompetence.

I remodeled with wood everywhere but the bathrooms which are marble tile.

The floors are the same level and have a completely smooth transition.

I have quite a bit of "subfloors" for my wood - self leveling layer - cork layer for soundproofing plus plywood which is how the wood is attached. I know they are significantly higher than the floors were and the bathroom and living/bedroom floors were all on the same level before the remodel so somehow my GC and his tile people made it all come together seamlessly.

FWIW it has been five years since I moved back in and bathroom tiles are not cracking or warped in any way.

I, too have flush-installed hardwood meeting up with tile. In my case, the tile was thicker. However, I had expert installers. I would be concerned that your installer seems stumped by this problem! How are YOU supposed to know how to do this? And even if someone gives you a good product to use, then would your installer know how to implement that product? Sounds like this is the wrong person for the job.

In my house we had 5/8” engineered floors so a layer of ditra decoupling membrane plus the thin set and tile made it flush. In my mudroom we needed to add thickness so the tile installer bonded a layer of 1/2” cement board to the floor with thin set then set the tile.

Agree that your tile installer does not seem to know his trade well. If it were me, I would be looking for another tile guy if you have to tell him how to do his job. What is the height difference? I would want a decoupling membrane over concrete (assume that’s what I’m looking at). That’s 1/8” for Ditra, then you have your mortar (as mentioned above, you want a medium bed), which could be as much as high as 1/2”, then you have your tile thickness (?). So are you concerned the tile will be higher than the hardwood or lower than the hardwood?