A shower pan is required in the floor of a shower to protect the subfloor from leaks and water damage.
Even a tile or stone floor runs the risk of leaking. Given the constant exposure to water and moisture, water leaks can prove to be potentially extensive and expensive damage, so most home builders and contractors will install a shower pan to protect the floor subfloor from water damage.
The primary way in which a shower pan protects the floor is by creating a barrier between the subfloor – usually made of wood – and the shower floor. In most cases, the shower pan is a thin layer of plastic and can be purchased premade. The plastic liner is placed at the bottom of the shower floor and also goes up the sides of the shower for several inches.
The pan is sloped toward the center drain so that any possible water leaks are directed toward the water drain. Some installers choose to create a slope before they place the pan down. However, others decide to create the slope after they have installed the shower pan by sloping the mortar that is spread over the shower pan in preparation for the shower floor installation.