If hes doing the whole fender,he may be using a "glaze".
Probably about 95 percent of it will be sanded off. I went thru the same deal with my truck, they called it "frosting" and dam near all of it ends up on the floor. But......when they were done,those ol beat up fenders were really,really nice!
With Bondo,,using a little less hardener gives you more working time.
