Tips for Waterproofing Under a Deck

Protective Gear

• Wear protective goggles or glasses when painting under a deck to keep drips out of the eyes. Also consider wearing a hat or hood to prevent drips on your hair. Gloves help protect the hands from the harsh chemicals in water repellents and paints.

Water Repellent Selection

• Use a water repellent preservative instead of just a water repellent. The preservative part of mixture contains chemicals that prevent mildew. Water repellent preservatives may also protect against insect infestations. When choosing a stain, look for one that contains water repellent preservatives, not just pigments and oils. Avoid varnishes and other surface finishes on exterior woods, because they quickly crack and let moisture contact the wood.

Applying a Water Repellent

• If possible, dip entire deck boards into water repellent preservatives before building a deck. Alternatively, apply generous amounts of a water repellent preservative with a brush. Make sure to cover the ends, joints and edges of each board. Use about 1 gallon for every 250 square feet of smooth wood. Use more for rough wood. Primer and paint can go over water repellent preservatives if you want to paint a certain color under the deck.

Maintenance

• Reapply water repellent preservatives every one or two years or any time the surface of the wood begins to turn silvery. To decide whether a water repellent has worn out, splash water on the wood. If the water soaks into the wood instead of beading up, the wood needs new water repellent. Clean the wood with a bristle brush, then reapply the water repellent preservative.