It's rare to find anyone installing a full-mud tile floor these days. The job is expensive and time consuming, and for the most part, it's become one of the lost trades.
Setting tile with thinset mortar over concrete backerboard or a plywood underlayment has been the preferred method for awhile now, and while this method can work well in many applications, it has shortcomings, especially if the floor system expands, contracts, bounces or otherwise moves.
Uncoupling membranes are the latest and greatest product to install between subfloor and tile. The idea behind an uncoupling membrane is that it can absorb the movement of a subfloor before that movement results in loose or cracked tiles. It works sort of like the springs in the record player you had a zillion years ago that kept your favor song from skipping when you were dancing on the living room floor.
When you watch this video, you'll see a graphic representation of how the Ditra uncoupling membrane, made by Schluter Systems
moves to accommodate the floor system's movement.
You'll also learn about Ditra's other advantages: it's easy to install, totally waterproof and extremely reliable.