If you are wanting to have a shower that does not have a typical dam this is one way to do it. This is a common desire for someone who may be handicap and does not want to step over a typical dam. In this case the concrete foundation was depressed 3″ below the bathroom floor. The concrete is then sloped and hot mopped to waterproof it. After the hot mop is complete the recessed area is then filled and sloped with approximately 2″ of mortar. Tile is then installed on top of the mortar and is set at the same height as the floor tile in the rest of the bathroom. This creates a barrier free shower. This can also be done on a sub-floor by recessing the framing.