Wood deck

Pressure or soft washing

The USDA Forest Products Laboratory explains why decks fur up. Power washing erodes the less dense earlywood faster than the dense latewood, leaving ridges behind. It describes a washboard surface with raised latewood as a sign of weathering or abrasion, including aggressive power washing¹.

Its advice is to keep the pressure low if you use a power washer at all¹. Olympic, which makes deck stains, says to use a fan-style or brush-like tip and set the washer at a low to medium setting². For previously stained wood, dark cedar and redwood, it recommends a deck cleaner and a garden hose instead of a power washer³.

Nozzle and pressure

Neither the Forest Products Laboratory nor Olympic gives a pressure number for decks, so we don’t either. Both say low.

Use a fan-style tip and never a jet-style tip, which can leave path-like marks around each board. Holding the wand too close can imprint lines and marks that stain won’t cover².

Cleaners to use and avoid

Protect plants and keep runoff out of drains

Cleaning chemicals can damage plants and grass. The Brick Industry Association’s advice holds for any surface: protect nearby plants, and where needed keep the cleaning solution and runoff off plants and the soil around them⁴. Soaking beds with plain water before and after, and covering what you can, is the practical version of that.

Street drains are not sewers. EPA reminds people that storm drains lead directly to local waterways, not to treatment facilities. Its tips for washing outdoors: use biodegradable, phosphate-free, water-based detergents, use as little as you can, wash on a driveway or yard rather than in the street, and send the wash water onto grass or gravel⁵. In Greene County, polluted runoff that enters the storm sewers is often discharged into local rivers and streams without treatment⁶, and Beavercreek asks residents not to dump anything down a storm sewer or drain⁷.

If you see suds, a rainbow sheen or an odd color in a ditch, stream or storm drain, Greene County asks you to report it to the County Engineer’s Office at 937-562-7500⁸.

Common damage

• Etched, furry woodPressure erodes the soft earlywood and leaves raised ridges of latewood that are hard to refinish¹.
• Wand linesA tip held too close leaves lines and marks that a stain can’t hide².
• Pulped surfaceSome commercial cleaners pulp the wood surface, and power washing afterward strips that pulp away¹.

When not to pressure wash at all

Step by step

1. Clear and sweepMove furniture and planters and sweep out debris between boards.
2. Protect the plantsSoak and cover plants around and under the deck.
3. Apply the cleanerBrush on a deck cleaner, or diluted bleach (1:5) for mildew. Don’t add liquid detergent to bleach.
4. Rinse with the grainRinse with a garden hose, or a power washer on a low setting with a fan tip, moving along the boards and keeping the wand back from the wood.
5. Let it dryLet the deck dry fully before you stain or seal, following the stain label.

Before you start, read the safety page. If the job looks bigger than you want to take on, DIY or hire lays out what each way involves.