coating problems

when i use epoxy speedcoat on a sanded(40grid)board, litle holes like fischeyes apear. It is the same effect as sillicon in carpaint, only more.It looks a bit like the coating goose open like water on a window. With laminate epoxy the problem is even worse. With the coating on the glaslayer i dont have the problem. Is it typical epoxy??How many(grams) sandcoat do i use for a 8 f.?