So you’ve decided to rent a pressure washer and clean your deck. Easy enough, right? But the job may not be as easy as you think. You’ll start by setting up the machine and hook up the water supply lines (assuming have a ¾ inch hose line). Then you attach the high pressure hose, the gun, and turn on the water. Pull the engine recoil cord and the machine starts. Point the tip toward the deck, squeeze the trigger, and water jets out.

So far, so good. You’re cleaning your deck, or so you think. You’ve done a lot more if you check your work and find that you’ve removed the dirt, but also ¼” of wood, leaving behind an etched surface far from the flat boards you started with.

Periodic cleaning is not only an important part of preventative maintenance to keep your deck beautiful, it will also save you time and money by preserving your deck. By following the tips below, you can safely clean your deck and enjoy it for years to come.

The pressure required to wash your deck surface rarely exceeds more than 1,500 pounds per square inch (PSI). That’s still enough pressure to damage soft wood and to leave composite decking with lap marks. Less is definitely more when it comes to pressure washing, which is a mechanism to remove embedded dirt and other contaminants. But excessive force will remove much more that soil from the wood. Rather than use too much pressure, the cleaning agent should do most of the work in removing the dirt.

There are many types of cleaners. Some are detergents, bleaches, or chemical solutions designed to react with certain woods. There’s no absolute rule which cleaner you should use, but whichever you choose, always follow the manufacturer’s directions. If you do use a pressure washer, remember it should be used to remove the chemicals as well as surface dirt. It also uses less water than a conventional hose and nozzle. Removing the cleaner residue is much easier with a pressure washer because it’s forced off the wood and diluted, so let the cleaner do its job.

You should have a stiff bristle brush in your deck cleaning equipment. Make sure it’s a synthetic, not natural bristle brush, as many cleaners will deteriorate natural bristle brushes. Investing in a good quality synthetic bristle will provide many years of use. The brush should be attached to a handle long enough to reach all the areas that need to be reached. One probably won’t work for all your needs, so it’s best to have several. The right tools make the job much easier.

  1. Scrub the deck. Lightly watering down the deck can help with the application and spreading of cleaners. Many solutions shouldn’t be allowed to dry on the wood so make sure you periodically spray or mist. Depending on how soiled the deck is, you may see immediate results. However, cleaners often require a minimal period of time to break down imbedded dirt and contaminants.
  1. Rinsing. Once the deck has been completely scrubbed, rinse with a conventional hose and nozzle. If you intend to use a pressure washer, follow the instructions in the following paragraph. Keep in mind that wood fibers may rise because of pressurized water applied to a wood surface, but they can be removed rather easily.

When turning on the pressure washer, always keep the trigger away from the surface, and from anything that can be damaged or harmed, such as windows, pets, and people. The water emerging from the tip is called a ‘fan’, which is rated in degrees. The degree of angle indicates fan size. Zero (0o) is typically a stream of water. Never apply a stream of pressurized water to wood. A 40o-60o (degree) tip size is standard for deck cleaning. Bring the fan to the surface where you want to sweep the deck.

  1. Begin sweeping. Start from the deck from the house side out. When you tip it from the surface, be consistent in the length to prevent lap marks. Sweeping a deck with a pressure washer is to remove dirt and leave no traces of the pressurized water. If you use too little pressure or keep the fan too far from the water, you’ll get a less clean surface. If the water pressure is too high or too close to the wood, you’ll get a stripped area. When sweeping the surface, begin and end with the same pressure.
  1. Feathering. This technique helps mask the starts and stops of the sweep. You’ll want to overlap previously swept areas, ensuring the point where the nozzle is closest to the wood begins at the point where the sweep ended on the previous stroke. Remember to always work with the grain or the length of the board. Though this technique requires more strokes and is slower, it does an exceptional job. It also ensures that as much of the cleaner as possible is removed/diluted. This is important because excess cleaner left on the deck surface can cause long-lasting and detrimental effects. Feathering is the best method for using a pressure washer on a deck surface.
  1. The “long sweep” is another method. This entails bringing the fan to surface and walking it along the length of the board. Keep the tip at the same distance from the deck from the beginning of the stroke through the entire length of the board. This method may require several passes, but it works well for decks without railings or obstacles that can cause problems with starting and stopping. Using this method with railing structures will leave behind a line across the surfaces where the fan stopped. They’ll be difficult to remove because more pressure must be applied. This can start a pattern of more and more pressure and risk damaging the surface.

Corners often present a challenge to pressure washer operators. With no direct place for the water to travel, debris and chemicals can splash back into the user’s face, which can be harmful. It’s important to always wear appropriate face and body protection.

When dealing with corners, engage the fan and bring it into the corner first to spray out debris. Avoid working yourself into a corner by always working out of a corner. By doing so, you may cross grain spray for a short time. This should be no problem as long as the distance is greater and pressure lower on the cross grain than with the grain. An easy cheat to remember is the letter “L.” Long sweep into the corner, and short sweep out of the corner with the grain.

  1. Inspection. Once the deck is completed, let the deck to dry. Decks look very different wet than dry, and it’s easy to miss small imperfections when a deck is wet. It will also be almost impossible to remove raised fiber from a wet surface. If you chose a topcoat (sealant or stain) with a one-day application to be done after washing before the deck dries, it’s still recommended that the deck dry a minimum of 24 hours. Check your work once the deck has dried. There should be lap marks, minimal raised fibers, and clean wood. The surface should be consistent with no areas left unwashed or over washed. If this is what your deck looks like, congratulations on a job well done.