When it's time to clean your wood deck in preparation for refinishing, a chemical deck brightener applied by hand-scrubbing may not do the job of deep-cleaning, but a power washer will. Often a pressure-washer can effectively clean a deck with just plain water. However, a pressure washer can ruin your deck if it's not used properly. This is a tool that is powerful enough to etch brick, but in the right hands it can also be gentle enough to wash siding. If you use it with too much jet pressure or place the tip too close to the surface of your deck, you can deeply etch the wood and cause the fibers to splinter.
A pressure washer has many uses around the home, but if you prefer not to own one, you can always rent one from a home improvement center or tool rental outlet. It typically costs about $40 for a four-hour rental.
Equipment / Tools
- Pressure washer with a fan tip or rotating tip
- Sheets of plastic (optional)
- Random orbit sander (optional)
- Deck stripper/brightener (optional)
- Sandpaper (optional)
Select a Tip and Pressure Setting
Choose the appropriate pressure setting and spray tip for your application:
- Use the lowest possible pressure that is still effective. Pressure for soft wood (like cedar or pine) should be at about 500 to 600 pounds per square inch (psi); harder woods may tolerate more pressure, but you should not go higher than 1,200 psi.
- Use a fan tip with a 40- to 60-degree spread. A rotating tip is also suitable if you use it carefully.
- Test your pressure and its effectiveness in an inconspicuous area, such as a stair tread. If you find it necessary to replace a piece of wood because you etched it, a stair tread is easier to replace than a surface deck board.
Power Wash the Deck
Start with the pressure at 500 to 600 psi and test it on an inconspicuous area. Increase the pressure incrementally as needed to clean the deck without damaging or etching the wood surface.
Engage the trigger while holding the wand tip a couple of feet away from the deck surface, then lower the wand to about 12 inches above the surface. Clean the deck with a sweeping motion, and avoid the tendency to pivot with your arm, which will result in an inconsistent distance between the spray tip and the deck surface. Try to maintain a consistent distance by moving your arm laterally back and forth.
Clean the deck boards from the house outward. Work with the grain by feathering the spray lengthwise, parallel to the deck boards, and overlapping each area slightly. The goal is to achieve even cleaning with no "hot spots" or visible "cleaning edges."
Apply a Chemical Stripper/Brightener (Optional)
If the wood is badly darkened or stained with mildew, washing with a deck-cleaning solution that includes sodium hydroxide can help brighten it. Look for a product designed for brightening deck wood and for use in a pressure washer, and make sure your pressure washer allows for the intake of cleaning solutions.
Mix up the solution as recommended by the manufacturer. Apply the stripper solution in the same manner as when pressure-washing with plain water, then rinse by pressure-washing again with plain water. Stripper/brightener products tend to roughen up the wood fibers, so you will generally need to sand the deck completely before re-staining or sealing the wood.
The chemicals in deck strippers/brighteners are toxic to plants, so make sure to shield shrubs and garden plants around the deck with sheets of plastic before using stripper with a pressure sprayer.
Sanding After Washing
Ideally, power washing a wood deck will not ruin the wood and etch or erode the softwood fibers. However, when wood gets wet, the fibers may become raised, creating a rough surface. This is a particular problem on handrails, where the raised fibers can lead to splinters. Make sure the wood is dry before sanding.
You have a couple of options for remedying this problem. If you did a great job of power washing with minimal damage and you just want to clean the deck, you may be able to get away with a spot-sanding here and there. But if you are going to refinish (re-stain or reseal) the deck, you will need to sand the entire deck to create smooth boards with little to no splintering. Sanding also opens up the wood's pores so the wood soaks up the sealer or stain consistently.
When sanding, do not use very fine sandpaper, since this can clog the pores of the wood and prevent the stain/sealer from readily soaking in. For the handrail, use no finer than 100-grit sandpaper. For the deck surface itself, use a 60- to 80-grit sandpaper. The best sander to use for a wood deck is a random orbit sander with a 5-inch sanding pad.