Sanding a piece of wood tears at the grain and even after the finest sanding this torn grain is evident almost as soon as a finish is applied. Nine times out of ten the torn grain will swell and stand up in the finish, giving you the feeling that sand has been thrown on the work. This sanding sealer is designed to raise that nap of the grain making it stand up and become brittle. It can then be sanded off with fine grit abrasive paper, giving a silky smooth base for you to apply your finish with no fear of the nap raising again.