If your contractor is installing traditional tile, it needs to be over cement board, or a kerdi liner. Wood moves, and this could lead to cracks. Almost any tile can be made to float by using this plastic tray made to hold the tiles. I don't have much experience with floating tiles, and if it costs the same from what I can tell, I would stick with the tried and true method.

Thanks for quick reply! It's 18" travertine tumbled stones in Versailles pattern. Other contractor said floating prevents cracking i with any movement. We are in Ca. Wonder why he is not floating. I will ask, but wanted to get advice here before.

After some research I now understand a bit more, Seems the question is whether to float the floor or use backer board....like Hardiboard, I think floating is more difficult but better at preventing cracks with any future movement. My guy is not floating...should I be concerned?

If by floating the floor you mean they're going to put down a dry bed to isolate the tile from the subfloor, as long as they know what they're doing it's a good thing.

In my house we've used Ditra, which is the modern equivalent for those of us who don't know how to do it properly any other way. Orange waffle type material with a fibre backing.

Thinset on the subfloor, then Ditra. Then thinset on top of Ditra which works its way into the waffle shaped surface and locks in mechanically, not by adhesive so much. Tile goes on this bed of thinset.

If the subfloor moves, less movement is transferred to the tile.

I wouldn't install a natural stone floor without it. My 2nd floor bath is on 2x8 joists that span 15 feet (true 2x8 lumber - 90 years old) and the laundry room is right next to the bathroom. 3 years in and the 80 sq ft of 12x12 inch marble tile and grout doesn't have any cracks.

Just put 30 sq ft of marble on the basement slab - used Ditra there too. Works with heated floors as well - heating system goes under the Ditra. My bathroom floors can go to 90 degrees no problem.

Hardiboard etc. has nothing to do with a floating floor. It's just another subfloor material. You want 2 layers of plywood at least 1 1/4" thick total (if I recall) for stone floors. Don't need cement board under tile. People use it on shower walls etc. as it's less prone to damage from moisture but if you're getting moisture to your surface under the tile you're pooched whether its drywall or concrete board. That's why showers always need Kerdi or another waterproofing layer between the tile and the wall.

Thanks so much Toronto Tom for your reply. I've a better understanding now.