Cleansing a 300 square base typically takes 1 - 2 hours. When you want to seal the grout with a polyurethane finish, we suggest waiting 24 hours after washing before applying the sealant to ensure proper adhesion. It takes 2 to 3 hours for the grout to seal itself. The length of time is dependent on the diameter of the tiles, the quantity of dirt in the grouting, and the shape of the room.