Originally Posted by
Mike45plus
Tiled shower floors are installed on a bed of cement that has been poured in a sump area created by the surrounding walls and saddle or threshold. This sump area is lined with a water proof membrane ( sheet lead was used in the old days ), typically sheet rubber or vinyl. The purpose of this liner is to collect, and direct water into the shower drain, if the water gets beneath the tile ( via a crack or open grout joint ) and cement during a shower.
The liner must be installed on a pitched subfloor so that any water that gets into the pan will move towards the drain, and prevent pooling of water and organic material ( soap scum, hair, skin, etc. ) When pooling occurs below the cement, the water and organic material will fester & breakdown, producing offensive odors.