Charlie:
The Evercoat comes with its own hardener which I think is PVA based (whatever it is, it smells awful). When I wanted to thin it for spraying I used regular acetone which is also good for cleanup. I found it helpful to lightly sand a larger area than I was going to repair, then mask off the repair area as a smaller section (of what was sanded) that I would use the new gelcoat on. So you went from old gelcoat, to the sanded area, to the newly sprayed area. This allowed the colors to blend a little better than just spraying new gelcoat on the old gelcoat.
ROY