I just finished applying 2 coats of Defy Extreme Wood Stain to my deck. The deck is on the North side of the house and the wood is pressure treated lumber. The deck was built 25+ years ago. Would it be helpful to seal the deck? The deck is 32×14 foot with seating around part of it along with stairs. It is a very large deck to clean and treat so I wondered if sealing it would extend the life of the stain?