Watco Exterior Wood Finish is a unique, penetrating oil that hardens in the wood, not on the wood. New, old, or pressure-treated lumber becomes water-repellent, provides ultraviolet and mildew protection, and resists warping and swelling caused by changes in weather. Watco Exterior Wood Finish is durable and easy to use. It seals and protects in one easy step. The exterior wood finish will not crack, chip, or peel. It is ideal for decks, siding, fences, and more.