i only put three layers of mat down at a time. i have done more and it seems like it take alot longer for the bottom layers to dry, and if the resin has wax in it sanding wont help it by getting the wax off all its doing is allowing the resin to sit in a a bunch of tiny grooves instead of a flat surface and wont come apart as easy. but i use a bonding resin it take no sanding it stays tacky between coats. it just depends on what your trying to make.