Can You Build a Shower Pan Without a Pre-Slope?

Pre-Slope Definition

• The pre-slope of a shower pan is built below the liner that is designed to capture almost all of the water that drains in the shower. This is usually created by sloping the mortar bed that sits below the tile or other finishing material. Some contractors slope the plywood support bed or install special tools for developing the pre-slope before the mortar bed is laid.

Importance

• The pre-slope channels the water used during a shower towards the drain. Without this encouragement, the water would soak into the floor below the shower pan because grout isn't completely waterproof. A sloped mortar bed causes any moisture that gets beneath the shower liner to continue to run towards the drain instead of soaking into the floor or walls. A flat mortar bed below a sloped liner or tile floor will allow water to stand and gather.

Consequences

• If the pre-slope is not properly built in your shower pan, water will sit and cause the floor below it to rot. Mold and mildew will also develop where water doesn't drain correctly. This is why the Uniform Plumbing Code requires all shower pans to have a pre-slope of at least 1/4 of an inch for each foot of distance away from the drain. A lesser slope than this violates building code.

Pre-Slope Tools

• There are a few products that make adding the correct pre-slope to your shower pan much easier. Instead of building the entire thing from scratch, consider using a fiberglass shower pan that is already sloped. Many of these models are designed for being finished with tile and can save time over leveling the mortar bed yourself. If you are building a custom shower pan from scratch, consider using pre-slope measurement tools. These are small plastic bars that show the correct level of slope. You simply add the mortar around them until the surface of the mortar bed is level with the slope of the bar.