The tile guys "installed" the shower pans. Traditionally, this has been a shallow "pan", custom formed from a copper or rubber sheet, that is installed on the floor and a few inches up the walls to prevent any water from seeping out of the shower's base. (Tiles are applied over the pan, so you wouldn't know it's there unless you saw it being installed). The problem with rubber/copper pans is that they're tough to make fit perfectly, so the latest method is to create a pan out of liquid rubber. The liquid, about the consistency of rubber cement, is poured on and spread around the shower floor and 4" up the walls, covering everything about 1/8" thick. It cures in 36 hours, after which it's a completely waterproof, perfectly formed membrane.