While you can lay concrete in your shower prior to installing a shower pan, concrete does not serve as the shower pan itself. Rather, concrete provides a solid base for your shower pan material. A completed shower is not waterproof. The shower pan collects water that leaks beneath the tiles and directs it down the drain. Concrete will absorb water without effectively redirecting its flow. Thus, a concrete slab alone does not serve as an effective shower pan.
The material you choose for a shower pan depends on your budget and preferences. John Bridge of John Bridge Ceramic Tile in Houston, Texas recommends installing a shower pan made of poly-vinyl chloride. While you must eventually replace most shower pans, a shower pan composed of poly-vinyl chloride can last indefinitely. Chlorinated polyethylene is also an effective shower pan material. It is long lasting and holds its shape well after installation.
Not all installers lay a concrete base before installing a shower pan. The concrete base, however, saves you money later on if your shower pan develops a leak. The leaking water seeps into the concrete base, slowing the degree to which it soaks into sheetrock, wooden wall studs and your subfloor. Thus, taking the additional time to line your shower base with concrete before installing your shower pan can help you avert expensive shower repairs in the future.
The amount of concrete you need when constructing a base for your shower pan will vary depending on the size of your shower. Mix the concrete according to the manufacturer's directions. Spread the concrete out in the shower with a trowel. When installing a concrete shower base, it's imperative that you spread the concrete around, rather than over, the drain hole. Even partially blocking the drain hole will disrupt the flow of water down the pipes. Creating a slight downward slope with the concrete helps the shower pan dispose of excess water. Remember, the shower pan itself sits on top of the concrete base. If you want a sloped shower pan, you must first create a sloped concrete base. Let the concrete dry completely before installing the shower pan.