We are renovating a very damaged 18X36 rectangle pool (steel walls, cement floor) We are not experienced, and have lots of questions. This is what we need to know first:

How important is the cement mix at the bottom of the pool? I mean, I know it's important, but MUST it be a specific cement/vermiculite mix? We are thinking about doing regular sand mix cement and laying a thin layer of styrofoam sheeting over it (since, being novice, we expect the floor not to come out perfect) The styrofoam layer is not specially made for inground pools...it is actually found in the plywood section of home depot from what I am told.

Sound hairbrained? Or it just might work?