Please don't use Behr products for your deck. Because of their products, we ruined our deck. We got an estimate for around $500 to powerwash and treat it. Our deck is about the same size as yours. Of all the deck refinishers we talked with, everyone said they would never use Behr products. Behr reimbursed us for the stain and supplies we bought PLUS the cost of refinishing it professionally. They must know their products are no good.