The process of building your own shower pan, though not difficult, is very involved and is a lot of work. For best results and a successful, watertight finished product, each step should be completed carefully and allowed to dry. The steps involving cement mortar are two of the most important steps in the process because the mortar creates the foundation and the contour of the shower pan.
Cement-Based Mortar Mixes for Shower Pans
There are a few types of mortar that can be used to build a shower pan. They are sand mix, Type N mortar mix, Type S mortar mix and unmodified thinset mortar. Sand mix is the most commonly used mortar for building shower pans. Type N mortar mix us also used to build non-load-bearing masonry walls. Type S mortar mix is also used to build load-bearing walls. Of the two, Type S mortar mix would be the best product to use to build a shower pan because it is formulated for strength and durability. Unmodified thinset mortar is very similar in nature and formulation to sand mix. The sand included in unmodified thinset mortar is very well ground and very fine-feeling to the touch. The sand in the cement acts as an aggregate just like gravel does when working with wet cement. The net effect is that the sand strengthens the cement so it will not crack, split, crumble, shrink or otherwise fail. Use the mortar mix that best suits your project's needs.
Creating the Drain Slope (The First Mortar Layer)
The mortar mixes named above are commonly used because they use various sizes and amounts of sand as an aggregate product instead of varying sizes of gravel. Sand strengthens the Portland cement that is the hardening agent in the mixture but also allows the mixture to be easily worked and smoothed with tools.
The main function of the mortar mix is to create the slope of the shower drain. The slope of the shower floor should be 1/4-inch per linear foot that the shower floor drain is away from a barrier (wall, step). For example, if the drain is four feet away from a wall, the mortar will be one inch thick at the wall sloping to 1/4-inch thick at the drain. The drain may not be exactly in the middle of the shower floor but the ¼-inch-per-foot rule still applies.
Use a straight piece of wood to pack the mortar and to create a nice, even slope on the shower pan floor. Then use a concrete finishing trowel to make the top of the first mortar layer smooth. Let the mortar dry for at least 24 hours.
Finishing the Shower Pan (The Second Mortar Layer)
The first mortar layer in no way waterproofs the shower pan. Install a vinyl pan liner and test for water tightness before the second mortar layer is installed. The second mortar layer is installed on top of the vinyl shower pan liner with the final, finished slope. The second layer is much thicker than the first layer. The thickness of the second mortar layer must be at least 1-1/4 inches around the drain itself. In keeping with the previous example, the total thickness of the mortar layer at the wall will then be 2-1/4 inches if the drain is four feet away from the wall.
Finish the second layer of mortar in the same way the first mortar layer was finished. Use the wood to pack the mortar and to create a nice, even slope on top of the vinyl liner. Use a concrete finishing trowel to make the top of the first mortar layer smooth. Let the mortar dry for at least another 24 hours.