How to Seal a Deck With an Air Sprayer

Rot and fungus will ruin your wood decking boards if you don't seal them against moisture, especially if the deck is in the shade or surrounded by foliage.

Shaded decks need extra protection against moisture.
Although you can apply most sealers with a paintbrush or roller, it's usually easier and more effective to spray a sealer. An air sprayer gives you more control and wastes less than an airless sprayer and is more suitable for spraying thinner materials like sealers. Even though the gun produces less overspray than an airless sprayer, there is still enough to be harmful, so wear a respirator. .

Mix a solution of deck-cleaning detergent and warm water in a bucket, and spread it over the deck with a mop. Let the detergent soak into the wood for 30 minutes to an hour, and then wash it off with a power washer. This will remove mold, grime and oxidation from the wood and return it to its natural color. Let the deck dry for 24 to 48 hours.

Connect an air gun to a compressor with an air hose. Use a hose that is long enough to allow you to reach as much of the deck as possible without moving the compressor. Plug in the compressor, and allow it to develop a pressure of 35 to 80 psi. If you are using a high-volume low-pressure gun, adjust the maximum pressure to a lower setting according to the manufacturer's instructions.

Unscrew the cup and fill it about 3/4 full with sealer. Screw the cup back on, and turn the nozzle to get a vertical spray pattern. Hold the gun as close to upright as possible but with enough of an angle to deposit material on the deck surface. The tip should be 6 to 12 inches from the decking.

Start spraying the farthest reaches of the deck, and work back toward the entry. Spray in a back and forth motion, overlapping the spray pattern by about 50 percent on each pass and keeping the tip a uniform distance from the surface at all times.

Let the sealer dry, and then spray a second coat, moving the gun perpendicular to the direction you moved it when you sprayed the first coat. Spraying in a crosshatch pattern in this way is insurance against leaving areas without sealer.

Pour out the remaining sealer when you are finished, and fill the cup about half full with the thinner recommended by the sealer manufacturer. Spray the thinner through the tip for about 20 seconds, and then swish the cup around and unscrew it. Unscrew the tip of the gun, and drop it in the thinner. Leave it there overnight or until you are ready to use the gun again.

Things You Will Need

  • Deck-cleaning detergent
  • Bucket
  • Mop
  • Power washer
  • Air gun
  • Air hose
  • Compressor
  • Sealer
  • Solvent


  • Spray the steps, fascia, railings and foundation the same way you sprayed the decking.


  • If the deck is over a garden or patio, cover the ground underneath with plastic before you spray.
  • A pressure washer can damage the decking boards if you hold the tip too close to the wood.

About the Author

Chris Deziel has a bachelor's degree in physics and a master's degree in humanities. Besides having an abiding interest in popular science, Deziel has been active in the building and home design trades since 1975. As a landscape builder, he helped establish two gardening companies.