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A Guide to Power Washing a Wood Deck
When it's time to clean your wood deck in preparation for refinishing, a chemical deck brightener may not do the job of deep-cleaning, but a power washer will. At the same time, a pressure washer can ruin your deck if it's not used properly. A power washer, or pressure washer, can be powerful enough to etch brick or gentle enough to wash siding. If you use it with too much jet pressure or place the tip too close to the soft wood, you can deeply etch the wood and cause the fibers to splinter. There are three basic steps to doing it right:
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- Pressure and tip selection
- Power washing technique
- Post-washing sanding
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Pressure and Tip Selection
Choose the appropriate pressure setting and spray tip for your application:
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- Use as low a pressure as possible while still being effective. Pressure for soft wood (like cedar or pine) should be at about 500 psi 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 mess up and have to replace a piece of wood because you etched it, a stair tread is easier to replace than a deck board.
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Power Washing Technique
Follow a few tips and safety rules for proper power washing technique:
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- 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 but not damage or etch the wood surface.
- Engage the trigger a couple of feet away from the deck surface and then lower the wand to about 12 inches above the surface.
- Clean the deck with a sweeping motion of the wand. As you sweep, you will have a tendency to pivot with your arm, but that 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 from the house outward.
- Work with the grain by feathering the spray lengthwise, parallel to the deck boards, and overlapping each area slightly. The key is to achieve even cleaning with no "hot spots" or visible "cleaning edges."
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Sanding After Washing
The key with power washing a wood deck is to not ruin the wood and etch or erode the soft wood fibers. However, wood is wood, and when it gets wet, the fibers become raised, creating a rough surface. This is a particular problem on handrails, where the raised fibers can lead to splinters.
You have a couple options for remedying this problem: If you did a great job with minimal damage and you just wanted 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 need to sand the entire deck. It is not too difficult and will result in 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 or the stain/sealer will not soak in readily. For the handrail, use no finer than a 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 orbital sander with a 5 inch sanding pad.