Ditra is a barrier that can go over concrete. In comes in sheets. It really works well. It is lightweight and super-strong. I’m using it in more and more of my tile work.
“Designed specifically for ceramic tile and dimension stone installations, DITRA serves as an uncoupling layer, waterproofing membrane, and vapor management layer that accommodates moisture from beneath the tile covering. Further, DITRA performs all these functions while still providing adequate support/load distribution for the tile covering.”