That's an excellent and very practical question! The short answer is: it can be, but you must proceed with extreme caution. A pressure washer is a powerful tool, and using it incorrectly on wood can do more harm than good.
Think of wood like your skin. Too much pressure or holding the nozzle too close will cause damage. High-pressure water can actually gouge the soft grain of the wood, creating splinters and a rough surface. It can also force water deep into the wood's pores, leading to prolonged moisture retention, which is the primary cause of warping, cracking, and rot.
If you decide to use a pressure washer, follow these critical steps:
1. Use the Widest Tip: Always start with the 40-degree white tip (the widest fan spray). Never use a rotating or zero-degree tip.
2. Keep Your Distance: Maintain a distance of at least 12-18 inches from the wood surface. Start farther away and move closer only if necessary.
3. Mind the Grain: Spray along the direction of the wood grain, not against it, to minimize fiber lifting.
4. Pre-Treat with Cleaner: Apply a dedicated wood cleaner or a mild soap solution first. Let it sit to loosen dirt and mildew.
5. Work Quickly: Don't linger on one spot. Keep the wand moving constantly to prevent concentrated damage.
For most routine cleaning, a gentler method is often superior and safer. Mix warm water with a wood-safe cleaner or a bit of mild dish soap. Use a soft-bristle brush to scrub the surface, then rinse thoroughly with a garden hose on a gentle shower setting. This method effectively removes dirt and grime without risking the structural integrity of the wood.
After any wet cleaning, whether with a pressure washer or hose, allow the bench to dry completely in the sun for at least 48 hours. Once fully dry, applying a fresh coat of sealant, stain, or outdoor wood oil is highly recommended to protect it from the elements and future dirt buildup.
In summary, while a pressure washer on its lowest setting can be used for heavily soiled benches, the risks often outweigh the benefits. For long-term care and preservation of your wooden park benches, gentle hand washing and regular sealing is the winning strategy.