Plastic Before Pouring

Vapor barrier. Use 6 mil plastic and do it like this.

http://www.youtube.com/watch?v=2cNiBGe35MI

yes, plastic is a vapor barrier, but it's usually used to prevent the concrete from setting too fast. without the plastic barrier, the concrete will set up before it can be finished.

lay the plastic across the substrate and run the ends of the plastic up the forms stopping 1" below the top of the forms.