How to Install and Level a Shower Pan Base

Begin by thoroughly cleaning the shower alcove subfloor, removing all dust, dirt, and construction debris. If a drain hole does not already exist, use the shower pan as a template to mark its location and cut the appropriate size hole using a jigsaw. Place the shower pan into the alcove without any adhesive or mortar (this is the 'dry fit'). Press it firmly against the wall studs. Use a 4-foot level to check the top thresholds for levelness. This initial check confirms if the subfloor is reasonably level. Use a pencil to trace the outline of the top of the pan's mounting flange onto the wall studs. This line will serve as a reference later.

Turn the shower pan upside down on a protected surface. Following the manufacturer's instructions for the shower drain assembly, apply a continuous bead of 100% silicone caulk or a ring of plumber's putty to the underside of the drain flange. Insert the drain fitting from the top side of the pan so it sits flush. From the underside of the pan, slide the rubber gasket over the drain threads, followed by the friction washer (if included), and then thread on the locking nut. Hand-tighten the locking nut, then use channel-lock pliers or a dedicated drain wrench for a final quarter-turn to create a watertight seal. Scrape away any excess putty or caulk that squeezed out.

Lay a sheet of roofing felt or heavy-duty builder's paper over the subfloor area where the pan will sit. This acts as a slip sheet, preventing the mortar from bonding directly to the wood and allowing for micro-movements. In a 5-gallon bucket, add the dry mortar mix (a sand/topping mix is ideal). Slowly add water while mixing with a power drill and mixing paddle. Continue mixing until you achieve a thick, stiff consistency, similar to peanut butter. It should be able to hold its shape when formed into a mound and not be runny or soupy.

Using a trowel, scoop the mixed mortar onto the roofing felt in the shower alcove. Create several large, flattened mounds of mortar, each about 2 to 3 inches high. Distribute them evenly across the area where the pan's bottom will rest, ensuring the entire base will be supported. Do not create a flat, level bed; the pan will level itself when pressed into the mounds. Carefully lift the shower pan, align the drain assembly over the drain pipe, and slowly lower it into the alcove, pressing it down firmly into the mortar bed. The goal is to squish the mortar, forcing it to conform to the shape of the pan's underside and provide complete support.

Immediately after setting the pan in the mortar, place your 4-foot level across the top thresholds. Check for level side-to-side and front-to-back. Gently press down on any high spots to bed the pan further into the mortar until it is perfectly level in all directions. The pan's built-in slope will handle water drainage; your job is to level the top edges. Once level, drive 1-1/4 inch galvanized screws with washers (or galvanized roofing nails) through the pre-drilled holes in the pan's mounting flange and into the wall studs. Do not overtighten the screws, as this can crack the flange; drive them just until they are snug.

With the pan now set and secured, complete the final drain connection. The method depends on the type of drain assembly. For a compression-style drain, simply push the rubber compression gasket over the drain pipe and then tighten the compression nut on the drain assembly to seal it. For a solvent-weld (glue-on) drain, clean the inside of the drain fitting and the outside of the drain pipe with PVC primer, then apply PVC cement to both surfaces and quickly join them together, holding for 30 seconds. Regardless of the method, ensure a secure, leak-proof connection as per the drain kit's instructions.

The installation is mechanically complete, but the mortar must now fully cure to provide the necessary strength. Follow the mortar manufacturer's instructions, but generally, you must wait a minimum of 24 to 48 hours. Do not allow anyone to stand in the pan or place any heavy objects on it during this time. After the curing period, step into the center of the pan and shift your weight around. It should feel completely solid, with no flexing, creaking, or movement. If it feels solid, the installation is successful and you can proceed with installing cement board and tile.