How to Pressure Wash a Wood or Composite Deck

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Routine pressure washing will keep your deck free of dirt buildup, dislodge leaves and other debris stuck between boards, and help to maintain the beauty -- and safety -- of your deck. Not only can leaves and other debris pose slipping hazards as they decompose, but they can also trap moisture that promotes rot, requiring you to replace the deck boards sooner than expected. 

Ideally, you would pressure wash your deck at least once a year to remove algae and mildew and prevent other conditions that can harm your deck. 

If you have a wood deck, you should also pressure wash it before applying any stain or sealer. This will help the stain and/or sealer adhere better to the deck boards and prolong protection against the elements. 

The average cost to rent a power washer is approximately $50 a day, and it’s well worth the money. After all, pressure washing, when done correctly, will add years of life to your deck. It’s also a huge time-saver compared to hand scrubbing and rinsing with a garden hose.

Here is everything you need to know about using a power washer on your deck, including how much pressure to use on a composite vs. wood deck. 

How Many PSI Do I Need to Pressure Wash a Deck?

The pressure you need to wash your deck’s surface can vary. Less is more when it comes to pressure washing wood or composite decks. For composite decks it’s recommended that you can use up to a 3100 psi to pressure washer your deck. You only want to use enough pressure to remove embedded dirt and other contaminants. Excessive forces on the wood will remove much more than you want to remove and can leave lasting marks or impressions. Use your eye and your judgment to determine the best pressure level for your deck’s surface. 

Pressure Washer PSI by Deck Type

When power washing a deck, the type of material your deck is made from will determine the proper PSI to use to safely clean it. 

• Composite decking – Check your decking manufacturer’s guidelines to ensure you are following their recommendations for cleaning decking with a pressure washer and to avoid damaging your deck.
• Softwood decking - For softwood decks like redwood or cedar, 1,200 PSI is enough pressure. Anything greater than that and you risk damaging or removing the wood, leaving behind a raised grain. 
• Hardwood decking - Hardwood decking can typically withstand a bit more pressure than softwood. When pressure washing a hardwood deck, stick to between 1,200 and 1,500 PSI to prevent accidental damage to your decking.

What Deck Cleaner Should I Use in My Power Washer?

Cleaners come in a variety of formulations with different performance claims. Some are detergents, others are bleaches, and still others are chemical solutions designed to react with certain woods. There is no one clear answer as to what cleaner you should use. 

Your best deck cleaner options depend largely on the type of material used in the construction of the deck. Whichever cleaner you select, be sure to read the manufacturer’s directions carefully, and follow them to the letter. Then let the pressure washer do its job. A pressure washer uses less water than a conventional hose and nozzle. Removing the residue of the cleaner is far easier with a pressure washer than with a garden hose because it forces the cleaner out of the wood rather than merely diluting it.

How to Power Wash a Deck

1. Scrub the Deck with a Bristle Brush

A stiff bristle brush should be a part of your deck cleaning arsenal. For optimal results, the brush should have synthetic vs. natural bristles, because many cleaners will deteriorate natural fibers. A good synthetic bristle will last many years. The brush should have a handle long enough to reach all the places you need it to reach. Rarely will one brush work for all your needs, so if you need multiple brushes, get them. The right tool for the job can make all the difference.

Scrub the deck. Sometimes lightly watering down the deck can assist you in applying and spreading the cleaning solutions. Many solutions should not be allowed to dry on the wood so periodic spraying/misting may be required. Depending on how dirty the deck is, you may see immediate results. More often, the cleaner must remain on the deck for a short time to break down the embedded contaminants.

Once you have scrubbed the entire deck, you are now ready for rinsing. Again, a conventional hose and nozzle may work. But, if you are going to use a pressure washer, this next section will instruct you on the correct techniques. Note: Sometimes applying pressurized water will raise wood fibers at the surface, even when you’re being cautious. These raised fibers can be removed rather easily. 

2. Power Wash the Deck

Before you pull the trigger of the wash wand, be sure it’s pointing away from the deck surface and away from anything else it could harm, including windows and people. The water that emerges from the tip is called a “fan,” and you can change the fan size by changing tips, which are rated in degrees denoting the angle. A zero-degree (0o) tip will typically produce a straight stream, but you never want to apply a straight stream to wood. A 40o to 60o tip is standard for cleaning a deck. Bring the fan to the surface where you want to clean the deck.

The Sweeping Method

Begin “sweeping” the deck from the house side out. Use a sweeping motion parallel to the wood grain and keep the length of the sweeping motions consistent to avoid lap marks. The goal in sweeping a deck with a pressure washer is to remove the dirt without leaving pressure marks. Applying too little pressure or holding the fan too far above the deck will result in a less clean surface. Applying too much pressure or holding the tip too close to the wood can result in marring the surface. In sweeping the surface, you want to apply the same pressure over the full length of each stroke.

The Feathering Method

“Feathering” is a technique that may help you mask the starts and stops of the sweep. With this technique, you want to overlap the areas previously swept, making sure that the point where the nozzle is closest to the wood begins at the point where the sweep ended on the previous stroke. Always working with the grain or the length of the board, this technique requires more strokes and is slower, but it does an exceptional job. It also ensures that as much of the cleaner is removed/diluted as possible. Excess cleaner left on the deck surface can have long lasting and detrimental effects. Feathering is the most efficient method for using a pressure washer on a deck surface.

The Long Sweep Method

The “long sweep” is another method. Using this method, you bring the fan to the surface and walk the fan along the length of the board. The tip should be at the same distance from the deck from the beginning of the stroke through the whole length of the board. This method may require several passes. This method works fine for decks that have no railings or obstacles where starting and stopping can be problematic. If you use this method with railing structures, you will leave behind a line across the surfaces where the fan stopped. These lines will be difficult to remove as more pressure will have to be applied, possibly damaging the surface.

Pressure Washing Corners

Corners can sometimes be a challenge because the water has no direct place to travel and often ends up in the face of the user. Airborne debris and chemicals can be harmful. Always wear appropriate body protection. When approaching a corner, engage the fan and bring it into the corner first, spraying the debris out. Try not to work yourself into a corner, always work out of a corner. In doing so, you may have to spray across the grain for a short time. This is fine as long as the distance is greater and pressure is lower against the grain than with the grain. 

3. Let the Deck Dry and Apply Sealer or Stain if Desired

Once you have completed the whole deck, put away the equipment and allow the deck to dry. Decks look very different after they dry. Small imperfections that may have gone unnoticed when the deck was wet can become apparent. Also, raised fibers will be virtually impossible to remove from a wet surface. If the topcoat (sealer or stain) you have selected is a one-day product to be applied after washing but before the deck dries, it is recommended that you allow the surface to dry for a minimum of 24 hours. Once the deck has dried, inspect your work. The surface should have no lap marks, minimal raised fibers, and clean wood. The surface should be consistent with no areas left unwashed and no areas over-washed. If your deck looks like this, pat yourself on the back for the fine job. The next step is to prepare for finishing with a sealer or stain.

Use a cleaning solution to scrub your dirty deck before removing the suds and dirt with a pressure washer.

More Deck Care Resources

Get more tips for caring for your deck:

• Removing Moss or Algae from a Deck
• How to Sand a Deck
• Deck Inspection Checklist