I AM SANDING IN PREP FOR VARNISHING MY CHESSIE 18 AND KEEP SANDING THROUGH THE EPOXY. AT LEAST I THINK I AM. BEFORE I CAN REMOVE THE LITTLE ROUND MARKS LEFT BY THE ORBITAL SANDER I SAND THROUGH AND GET LIGHT SPOTS WHICH I ASSUME MEANS I HAVE SANDED THROUGH THE EPOXY. I HAVE PUT 4 COATS ON THE DECK (WHICH IS WHERE I AM HAVING THE PROBLEM ) AND RE-COATED AFTER SANDING THROUGH ONLY TO DO IT AGAIN. ANY IDEAS WOULD BE HELPFUL.