You don't want to sand green epoxy. It will gum up and leave little white powder residue in the weave of the cloth which will be very visible as you later proceed. If that happens you have to dig out each little white speck with a sharp point, or I've discovered that a fine, stainless steel wire brush will remove the white specks. However...I do scrape between coats with a carbide scraper to knock down the humps and edges. I do more scraping than sanding in finishing the boat.