A shower pan rests on a base of concrete that both supports the pan and provides a waterproof barrier for the subfloor and floor framing. Mortar is the type of concrete product that works best for shower pan applications since it contains no gravel, allowing it to work easily and dry with a gentle slope. The slope directs water toward the shower drain. Mortar mixes for shower pans are blended with Portland cement, which is water-resistant when it hardens, and sand.
A walk down the cement aisle of a home improvement store reveals a vast range of concrete and mortar mixes. Each manufacturer uses its own marketing label for those products they make for installing shower pans. These mortars may be designed for other applications as well as for shower pans. Look for products that are made as a bedding mix or a floor mud. The packaging states the acceptable uses for the mortar and should list shower pans among them.