As part of our ongoing work for the owners of Namaste, a yoga studio and Sol, an organic sunless tan and spa studio in downtown Kirkwood, MO, we had to build 3 custom shower pans. Like with most jobs, there were some logistical challenges: the drains weren't centered in the floor as a result of the concrete slab being structural - it has steel cables in it to provide strength (there's a parking garage beneath the building), which can't be drilled through - and the existing concrete floor was fairly uneven. Also, given the ADA constraints, our preferred method of shower pan construction - the old school way with the PVC liner - was out the window.
We started by building our curb, which was a simple pressure treated 2x4 anchored to the concrete floor. We installed DUROCK on the curb and walls, and then drew out all the layout lines - to keep the shower pan perimeter fairly level and at the right height to maintain a proper slope down to the drain - we would need.
With our layout lines drawn, we applied some latex primer to the existing concrete slab to help the shower pan "mud" adhere to it. We then mixed up the shower pan "mud": Quikrete's sand/topping mix with some extra sand added in, which results, if done right, in the consistency of wet sand. When building a shower pan, you don't simply pour the concrete in so much as you sculpt it using a wooden float, which allows for creating the required slope to get water directed toward the drain. Following the installation of the "mud", we waterproofed everything with RedGard and after waiting for everything to dry, began installing tile.