Doesn't matter. You can use either a marble OR (for the OP's benefit) a wood threshold between tile and ANY other flooring material. The marble is thick also, is it meant to be a "bump" in the floor? I just cannot see it being flat to the tile and wood floor Although many people do request that a marble threshold be flush with their floor on atleast the bathroom side, this is actually wrong. Johnmari is right. The whole reason why marble thresholds used to be REQUIRED at all bathroom doors was to provide a small dam at the doorway to guard against minor flooding, from say, kids splashing in a tub, or a minor toilet overflow. Mowers-- you're doing fine. You were right to install that plywood. What you had before wasn't NEARLY enough, and what you've put down now brings it up to where it should be. One thing to think about-- instead of using 1/4" CBU, what about using Ditra instead? It's only 1/8" thick, as opposed to the 1/4" of the CBU, and it'll provide alot more protection against movement to your floor. As for the heating mats, I don't see a problem with that, either (OVER the Ditra, not under). About the only thing you'll have to do is undercut your bathroom door, and maybe use a flange extension on your toilet flange, if it's already set.

I'm feeling pretty ticked off at myself for even hiring those guys. We were planning on doing it ourselves, but we were just too flipping tired after all the work we've poured into the kitchen, we decided to go with our neighbor's recommended tile guys. We laid the backerboard and taped the joints, so at least we know that was done. I am really, really upset that I didn't do my research more, because it turns out they used premixed thinset. Which I now know is not good. So in between kicking ourselves, my husband and I now have to decide do we want to bring these guys back to fix one loose tile and a few poorly grouted sections, or should we do it ourselves? Live and learn, I suppose. Too bad it costs so much. Thanks for your input; I really appreciate it. I think we'll try to do the cuts, but if that doesn't work out it's good to know there are other options. Toni

You can do one of two things, if you don't want that strip. First, you can trun and tack the carpet at the edge of the tile with no transition (I don't care for doing this without having atleast a metal "L" strip to protect the edge of the tile) or, as you suggest, use a marble threshold, and butt both finishes up to either side of it.

A "threshold" is for an exterior door and provides weather protection and drains to the outside. For an interior door a raised "saddle" allows a small undercut on the door bottom and yet the necessary clearance for area rugs. If undercut size or rug clearance is not an issue you would only need a "transition" or "reducer" strip between the different materials (or material heights) which should be narrow and located so it can't be seen from either side of the door if possible. At tile flooring in bathrooms it is normally made of marble with a beveled edge.