The first step in pressure or power washing a deck has to include a warning to the power washer operator. The truth of the matter is that pressure washers were never really intended for use on wood surfaces. These high pressure machines are really designed for hard surfaces so the operator has to take great care when using on a deck. I know the guy at the rental company or the sales man at the local home store said cleaning a deck is a cinch, but actually it is much easier to become a “wood engraver” then you might think. I know what I’m talking about after having to attempt to correct the workmanship of many DIY’ers over the years. So please accept this warning so you don’t have to rent a floor sander next weekend to remove the traces of your cleaning effort. You will never need a machine capable of producing more than 1500 pounds per inch water pressure. Even at this power, it is very easy to damage your deck
Be sure to wear old clothes and safety glasses. You are going to get wet and you will get sprayed with the cleaning solution regardless of how careful you are. In many positions on your deck surface, such as in corners, the spray has no where to go except right in your face.
Having said that, pressure washing a deck can produce excellent results if you take your time and use the machine in the proper way. The first step is setting up your machine. You attach a 3/4 inch water hose to your machine. Now attach the high pressure hose with the spray wand. At this point, turn you water on. Do not attempt to start your machine until the water is connected since this can do damage to the pump section of your machine. When starting many gas powered machines you might find it easier to start if you squeeze the trigger until the water flows through your machine. Take a few minutes and be sure your over-spray will not damage any plants or outdoor furniture, etc. To prevent any damage from your cleaning solution, just cover with waterproof tarps at this point. Just remember, all that water and cleaning solution has to go somewhere. You don’t want to go out the next morning to find spotted plants or house siding.
The secret to cleaning decks is to let your cleaning solution do most of the work. Away from the deck, preferable on a driveway or hard surface walk, use your machine to get used to the power. Open the spray head to a wide spray or “fan” pattern since this is what you will use 99% of your time. You are going to use that “fan” spray to rinse off your cleaning solution. Even in this position, the spray will remove embedded dirt and cleaner with little effort.
There are literally dozens of deck cleaners on the market today. Some are simple detergents, while others contain bleaches and specific chemicals which react with certain wood types. I would strongly suggest against using household bleach. Stick with the commercial deck cleaning products to minimize the danger to your surrounding areas and plantings. Many of the larger deck stain manufacturers have their own deck cleaning products. Which ever product you chose, be sure to read and follow the manufacturer’s instructions. You will find that most instructions will not include any directions or suggestions of using a pressure washer. They are well aware of the dangers I mention above.
I’ve used pressure washers to power wash decks for decades now. They are most effective when used properly. If you are going to use a pressure washer, just remember the job of the machine is to remove the cleaning chemicals and the dirt. The additional benefit is that the pressure washer will use less water then a simple hose and nozzle The first step is to simply rinse off the entire deck with water at low pressure. After doing this, I mix the cleaner in a 5 gallon bucket and use the pressure washer to spray the decking with the chemical. I use an old broom or a commercial deck brush to further spread the cleaner around the surfaces to be clean. You don’t really have to scrub, just spread the cleaner at this point. Follow the instructions and allow the cleaner to set or dwell on the surface for the specified time. Do not allow the solution to dry on one section of the deck while scrubbing another. This will lessen the effect of the cleaner. On very dirty decks, you might even spray a second application of the cleaning solution and scrub the surface a second time. Remember; do not allow the solution to dry on the deck.
When you have scrubbed down the entire deck, steps, and railings, it is time to rinse off the cleaner and dirt. I must mention again, that a conventional hose and nozzle could be used. But if you are going to use your pressure washer, this is where many DIY’ers get into trouble. Remember how you experimented with the “fan” position of the spray wand? Be sure to retest and set you sprayer to this position. Use your sprayer from the house side, spraying away from the structure. Carefully go with the grain or direction of the flooring boards using the “fan” spray to actually sweep the deck. Also be careful because the pressure can actually raise the fibers on some older wood surfaces.
As you “sweep” the deck with the spray, try and be very consistent in the distance of your sprayer from the surface and the area you cover with each sweeping motion. Remember the distance to the surface translates into the pressure of the spray and the intensity with which it will wash the surface. This will help prevents lap marks on the surface. Don’t go too fast or get too close to the surface. You’ll develop your own technique as you gain experience. The ultimate goal here is to sweep off the cleaning solution and all the embedded dirt without leaving any lasting marks on the surface. I’ve read all sorts of articles giving detailed instructions and the simple truth is you have to gain experience as you go.
You will learn that you really cannot appreciate the results of your work until the deck has dried. When the surface is wet, it is not unusual to appear uniform and clean. Upon drying, you might be surprised at areas that are darker then others. My advice is leave the deck and have a cold drink or cup of coffee before cleaning up your equipment. If upon drying, you find dark areas, simply perform the above steps again, paying attention to the darker areas. But be sure to spray the entire deck to prevent spotting.
When you are satisfied with the results, turn off your water source. Before disconnecting the hoses from the machine, be sure to release the pressure through your wand. This makes the process much easier and will keep you dry. Pressure washing your deck should be viewed as regular preventative maintenance. If you are careful and routinely wash your deck each year, followed by application of an appropriate sealer, your wood deck will last for decades.