The Standard Slab Rough-in for a Shower Drain

Frame

• A shower pan rough-in starts with a wooden frame that builds the support and shaping structure for your slab. Use a 2-by-10 against the back wall of the shower to help stabilize the liner. Also, block between the studs on the sides of the shower with more pieces of 2-by-10 cut to fit in the gaps. The floor should be made of 3/4-inch plywood or a concrete panel. Build the leading edge from three stacked 2-by-4s. Rough in the frame for the entire shower at this point, not just the floor.

Slope

• It is critical to maintain the slope of the slab at every stage of the shower's construction. Check the slope after you add each subsequent layer while building up the shower slab. Ensure that you have a slope of 1/4 inch per foot leading towards the drain. This needs to be even from all sides if the drain is in the center of the shower, or a long slope from one side if you have an end drain in a rectangular or oval shower.

Layers

• The slab is built up in layers and the drain installed before the final top-layer of tile or a pre-fabricated shower pan is installed. The first layer is typically a thin layer of cement. You must carefully scrape the cement to follow slope lines marked on your surround boards to ensure drainage. After it dries, install a waterproof membrane designed for use in shower pans. Then, the final layers are built up using more mortar, metal lath and a final layer of mortar. The grade must be maintained with each subsequent layer.

Drain

• Throughout each stage of the build you need to install pieces of the drain. Before any work is done, you have to install an extension on the sewer pipe to bring the drain up to a level above the working area. Then, stuff a cloth in it so debris doesn't fall in while you're working. After the membrane is installed, a flange is bolted in place to the drain pipe. When the additional mortar is added, you have to put gravel or crushed tile over the weep holes so that it doesn't clog them. These holes drain water away that seeps through the tile in your shower. The final drain section is installed after the membrane is installed and sealed in place. It should be about 1 1/2 inches above the pan.