I'm installing rubber membrane in shower with appr. Drain can I use concrete for floor and then seal with epoxy type sealer

No, are you trying to build a custom shower pan and not use the proper materials. Look this over How to Build a Shower Pan

That's how an old fashioned method shower is supposed to be built. BUT, why not build a real good shower and make it "watertight" so you'll never have a leak, mold and it'll look great for many years because it'll dry out fast after use.

Consider a KERDI MEMBRANE & DRAIN shower. Picasa Web Albums - Tile 4 You Inc.

Jaz

I agree with Jazman and have been impressed with his tiling knowledge. Welcome to AMHD Jaz. I rarely see pros or builders doing a full mud shower anymore so I discourage DIYers from trying something no longer practiced. Its abit like teaching a newbie how to use a bit and brace when you have a 19.2 v Makita hanging from your belt, most new tecjhniques save money, time and labor.