I am putting in a custom shower on an existing cement slab.
I already have by drain stub up, what kind of morter can I use for the shower pan?

Thanks Everyone.

I'm a plumber, not a tile man. My job ends when I install the flange type shower drain and pan and test the shower for leaks. You have set the flange, panned out and tested the shower haven't you? Please repost your question to: Home & Garden/ Interior home Improvement. Good luck, Tom

I bought and istalled a pan recently from Home Depot, the instructions said to use plaster of paris for a setting material which I did in addition to securing the flange to the studs. Seems to be fine. I have heard of people using a cement based morter to do this as well.

Is this a prefab pan? If so, a brick mortar soft base will work great. Mix it thin and make sure it is level. Lowe's makes the best drain for it, the top unscrews and the bottom does not move after it is glued on. If anything breaks, it is usually the top. Buy a spare for if you ever break the top part of the drain.