One of the most frequent points of concern for our customers is tile’s ability, or inability, to keep water contained. Tile may slow down water penetration, but the grout joints in between tiles are made from cementitious materials which do absorb water.
In most of our state the plumber is required to install the rubberized pan/ vinyl material that keeps a shower from leaking to the subfloor below. Tile installers work on top of the pan, and any water that seeps through grout joints is, in a proper installation, directed to the weep holes of the drain flange.
The walls of a correctly installed shower are lined with tile backerboard which overlaps the pan material, deflects water, and directs it down to the drain.
ANSI approved tile backerboard is the preferred substrate for tile in a residential shower because it deters water absorption. Sheetrock and ‘greenboard’ will wick water like a sponge, and they are not approved surfaces on which to install tile in wet areas.
New trowel-able waterproofings are available to offer additional protection for seats and steam showers, but, in a standard shower, it’s the pan material that is actually the only ‘waterproofing’ component of the complex water management system.
Neuse Tile Service 
June 4, 2014 at 11:37 am
been a useful article, thank you.