This is the case with all of the proven laminating epoxies. Some have a shorter or longer working period. It is my opinion that you shouldn't sand green epoxy. First...it will gum up. Second...you will get fine white powder in any depressions...such as the weave of the cloth. These little specks may, or may not, show up as white specks as you continue with your fill coats. If you have any runs, drips, or errors....a carbide scraper will make short work of them. And...to top it off...I think too much is made of the chemical versus mechanical bond. I doubt if anybody can quantify this difference...or see it. One positive of recoating green epoxy is that blush is much less of a problem.