Ceramic floor tiles and marble can crack if your sub floor is not very sturdy. Schluter Ditra underlayment should be used to ensure that this doesn't happen. The Ditra Installation Video and installation handbooks ensure success.

Concern with Bathroom or Kitchen Floor
Cracked ceramic floor tiles are difficult to repair, so we wanted to do everything possible to prevent cracking. In our home kitchen remodeling project, we were concerned with the rigidity of our kitchen floor. The space was approximately 13 feet by 27 feet. As shown below, our sub floor was made of planks and on the advice of a ceramic tile installer, we put in 3/4 inch plywood, which we screwed in.

The plywood added rigidity, but the floor was still spongy when we jumped up and down on it. To complicate matters, another ceramic tiler said that we should have installed 1/2 inch Durock which we had used in our bathrooms. To make matters even worse, the transition between the kitchen and the adjoining rooms was becoming an issue.

Solution: Use Schluter Ditra
Schluter Ditra is an orange polyethylene mat with square, dovetailed recesses and an anchoring fleece laminated to the underside. It is as light as a feather and much easier to work with than Durock. Ditra really addressed our two major problems:

• provided adequate support and load distribution for the tiles, and
• Was only 1/8 inch thick, which minimized the kitchen floor transition problem.

Other Recommendations
Make sure you supervise the Ditra installation if your tiler has not worked with it before. Many ceramic tile installers are not familiar with and most are not going to read an installation manual either. So you have to do your homework.

The biggest mistake that a ceramic tiler will make is to insist on using a modified thinset to install the Ditra on both the sub floor and also to install the tiles. This is not correct. So hold your ground.

In the case of plywood sub floor, You can installed the Ditra on it using a modified thinset which has an additive in it. However, only use unmodified thinset to set the tiles on the Ditra. Unmodified thinset has no additives in it. It is dirt cheap also. For all other floors, following the instructions in the Ditra Installation manuals. They come in English,
Spanish and French [PDF].

Also watch the Schluter Ditra Installation Video which is about 8 minutes long. It won't win an Oscar, but you'll have a good idea of how to work with the Ditra. Good luck.