Let’s look at two underlayment scenarios:

Option one, either cement board or hardiebacker both are cement based and have separate advantages over the other. What they share or have in common are, there both heavy, present hight issues, labor intensive to install, and have weak points at the joints regardless of taping or not. If you have ever saw a series of tile with a hairline crack, your seeing the underlayment joint failing. the issues is the tile is stuck to the cement-board or hardiebacker and as the natural expansion and contraction process of the floor occurs stress is created and the weak points are exposed. Sometimes, if the board is not put down with a thin-set the voids under the board will allow movement or flexing, leading to cracking of the tile and grout joints.

Option two, Unoupling membrane (lots of brands on the market, Schluter Ditra was the first and one example), what is it? Uncoupler is a plastic based underlayment that has a mesh backing and pockets on the top side. The material weighs a fraction of cement based products, cuts easy so installation time goes down, you can use small pieces or patches, and no joints to tape. All of the listed factors make it a more cost effective product, and equal in strength to cement based products. Wait, I havnt’t even got to the best part. Uncoupler’s like Ditra allow for movement. Let me explain, the mesh attached to the uncoupler is meant to allow for the expansion and contraction process to take place separate from the plastic portion of the uncoupler and the tile. The result is, no cracking! One more advantage, uncouplers are natural moisture and vapor barriers.

I have used uncouplers for more than twenty years and have had zero issues and/ or call backs for cracking and/ or failed. The supposed down side to uncouplers like Ditra is the cost but again that is equalized in labor since uncoupler is faster to install. In the end both products have a place in the world of tile but if we are talking floor installs regardless of tile material, uncouplers are the clear winner.