How to Clean a Wood Deck and Treat Stains

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In one afternoon, you can use common household ingredients to clean stains, moss, and mildew on your home’s wood deck, with or without a power washer.

Patio table with an umbrella sits on a clean wood deck attached to a suburban home.

Wood decks develop permanent stains, splinters, mold, and mildew when not cleaned properly and sealed as needed. That’s because wood is porous, so it expands and contracts as the temperatures vary. As it expands, dirt and grime work their way beneath the surface, and when it contracts, that grime becomes a permanent stain. Fortunately, you can clean decking and get it looking good again with or without a pressure washer.

How To Clean Your Wood Deck

If you can’t remove everything sitting on your deck, you’ll have to work on two separate days, moving everything to one side of the deck while you clean the other and let it dry. After 24-48 hours of complete drying, you can do the other side.

Equipment and Materials You’ll Need:

  • A broom
  • Tarps to cover items below the deck
  • Bucket
  • Non-metal scrub brush or push broom
  • Garden hose
  • Oxiclean or homemade oxygen bleach
  • Power washer (optional)

Step 1. Sweep

Grab your broom and clean the exterior walls of the house where the deck attaches to it. Use the broom on your deck’s railing first and remove any cobwebs or other debris. Then sweep the top of the deck. If it’s a second-floor deck and you can get beneath it, clean the underside to eliminate debris that will collect moisture.

Step 2. Apply Homemade Deck Cleaner

This homemade deck-washing solution will clean your deck without damaging its finish and does not harm lawns or plants. You should still protect your furniture, BBQ grill, and outdoor toys with a tarp so they do not get coated with grime.

Make a deck cleaning mixture by dissolving 2 cups of powdered oxygenated bleach in 5 gallons of warm water. (If you are using homemade oxygen bleach, combine 1 cup of the liquid for every 1 gallon of water.) Working in sections, pour the mixture onto your deck and allow it to sit for 15 minutes. Reapply as needed, so the solution remains wet the entire time. You may see it bubble a bit as it tackles the stains. Use the brush or broom to scrub the surface, then rinse. Repeat this on the rails, stairs, etc.

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Step 3. Rinse

Once you’ve finished scrubbing everything, use the garden hose to rinse your deck from top to bottom, including the railings, surface, and stairs. Also, rinse any tarps you used to cover nearby items so they don’t dry with a layer of grime on them.

Step 4. Remove Stubborn Stains

Some surface stains, like algae or oak leaves, can be challenging to remove. To clean these stubborn messes on wood or composite decking, combine 1/2 cup of baking soda with 1 tablespoon of liquid dish soap in a small bowl to make a paste. Apply this to the spot and wait 5 minutes, then pour 1 cup of warm white vinegar on the area. The bubbling action should lift away the remaining stain. Rinse well with a garden hose as soon as the bubbling stops.

Step 5. Let it Completely Dry

Wood is fragile when wet, which means that patio furniture or your grill can gouge the wood or lift the grain, which will lead to cracking and warping in the future. Wait 24-48 hours before putting things back or sealing your deck.

How to Power Wash Your Deck

If you would rather power wash your deck, choose a time when there’s no rain or freezing temperatures in the forecast for at least a full week. Pressure washing sends water deeper into your deck’s surfaces than a hose, so the wood will take longer to dry.

Step 1. Sweep

Starting where your deck connects to your home, sweep with the wood grain to remove debris. Continue sweeping outward until you reach the railing. Sweep the stairs from top to bottom and, if it’s a second-story deck, sweep the underside of the platform as well.

Step 2. Use a Low-Pressure Nozzle

Although a power washer can make a weathered deck look new as it blasts away grime and discoloration, too intense pressure can damage your deck. Keep the setting under 1500 pounds per square inch. The white 40° nozzle is good for newer or lightly stained decks. You can switch to the green 25° nozzle for stubborn stains.

Step 3. Choose Your Cleaner

With a power washer, you may not need an additional cleaning solution. If you choose to use one, follow your manufacturer’s instructions to connect the cleaning solution tank to your machine. Many power washers have ports that connect to containers of commercial deck cleaners, so you don’t have to bother with mixing anything.

Step 4. Spray in Overlapping Strokes

Don’t aim the power washer at any one spot for long, and keep the nozzle at least 3 feet from the surface at all times. Use overlapping, long strokes following the direction of the wood’s grain. Start where the deck meets your home and work toward the rail, then reduce pressure to 1000 lbs/psi or the white nozzle to clean the railings.

Step 5. Dry

Once you’re done power washing your deck, use a broom to sweep away standing puddles of water so your deck can dry faster. Wait at least 48 hours before putting furniture or equipment back on your deck to avoid damaging or gouging the wood.

Deck Maintenance

Inspect your deck every Spring. At least once a year, check the flashing and ledger where your deck connects to your home. If you notice screws that have worked loose, replace them with new decking screws. If you see signs of rot, a licensed contractor may be able to replace only the damaged portion.

Sweep your deck weekly. Fallen leaves, roofing sand, and other debris can trap moisture on your deck’s surface and cause mold and rot. If you live in a snowy area, shovel your deck when you shovel the driveway but take care not to gouge the wood. Allowing snow to build up adds enormous weight to your deck, and the melting snow can also cause your deck’s wood to warp.

Sealing

If you plan to seal or paint your deck, deep clean it as directed, then let it dry for at least a week. To test whether it’s time to seal your deck, sprinkle a teaspoon of water on the wood in a shady spot. If the deck absorbs the water in 5-10 minutes, it needs to be sealed. Wait at least 24 hours after rain to seal your deck.

When you’re ready to seal your deck, use a pad or foam paint roller to apply the sealant or paint. For most decks, deep cleaning and sealing once a year is enough. Don’t go longer than three years without reapplying sealant, or your deck’s wood may begin to warp and split.


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