DO i only need one layer of thinset to tile over cement or concreat?

Question

Or do i put on one layer of thinset and let it dry overnight, and then put on another layer of thinset and tile let it dry then grout?

Answer 1

Ideally, you would want to put down a layer of a leveling compound, followed by a slipsheet (plasticized paper sheeting), and then let that set over night. Then you put down the thinset and tiles over the slipsheet. The slipsheet allows differences in thermal expansion between the concrete and the floor. This prevents cracking of the tiles and grout from uneven expansion and contraction of the materials.