Prior to pouring the floor, 6 mil plastic is laid and taped to create a vapor barrier below the slab. This goes down directly on the 6" of gravel that was placed. Any moisture that comes up through the gravel is stopped by the plastic.
Here is the plastic doing its job. The sun was out and moisture was coming up through the rock. You can see all of the moisture that would normally be in the slab from the ground.
The plastic is lapped up the wall and taped to the ICF foam. 2" of XPS foam (25psi) is installed over the foam, and taped as well.
Even though we are not installing infloor radiant heat, I am still putting down 2" (r10) of foam. This creates a thermal break between the ground and the slab. The foam touches the ICF walls, making the basement like a foam cup. It added roughly $1500 to the project, but it makes the floor more comfortable. Since there are bedrooms and a large family room down there (as well as a music/aux room) it was worth it.
All penetrations are taped as well.
Power troweling the slab.
Here is the finished slab later that afternoon. The north section was getting a lot of sun and was drying much faster than the south part. The south part was still dark gray almost a week later.
You can see the LVL ledgers and the anchor bolts cast into the wall. These hold the hangers we will put up for the floor structure.