Short answer
Use a wood-safe cleaner and a pressure washer set to low pressure with a wide fan tip. Work with the grain, keep the nozzle 8–12 inches from the surface, rinse thoroughly, then apply a wood brightener. Let the deck dry 24–48 hours before sanding high spots and sealing or staining.
Why this method works
Most damage from pressure washing comes from too much pressure, the wrong nozzle, or poor technique. Cleaners loosen grime so you can rinse at lower PSI, protecting the wood fibers. A brightener restores color, neutralizes cleaners, and preps the surface for finish.
Recommended specs
- Wood deck: 500–1200 PSI, 1.4–2.4 GPM, 25–40° nozzle
- Composite: up to 1500 PSI max (check manufacturer), 40° nozzle
- Tip distance: 8–12 in. from surface
Tools and materials
- Pressure washer (electric 1700–2000 PSI is plenty; gas is fine if you dial pressure down)
- 40° (white) fan nozzle; 25° (green) for stubborn spots; avoid 0° and turbo nozzles
- Wood/deck cleaner (oxygenated/sodium percarbonate)
- Wood brightener (oxalic acid based)
- Pump sprayer for chemicals
- Stiff-bristle deck brush on a pole
- Plastic sheeting or drop cloths to protect plants and outlets
- PPE: safety glasses, waterproof boots, gloves, hearing protection (gas units)
Step-by-step
1) Prep and inspect
- Remove furniture, grills, and mats. Cover nearby plants and electrical outlets.
- Tap down or replace popped nails/screws; secure loose boards.
- Sweep debris; use a putty knife to clear joints between boards.
2) Set up your washer
- Install the 40° tip. If your machine lacks a pressure regulator, increase your working distance to reduce impact.
- Connect to a GFCI outlet if using electric. Use a heavy-gauge outdoor extension cord only if the manual allows.
3) Apply cleaner
- Pre-wet the deck with a garden hose.
- Spray wood cleaner with a pump sprayer. Keep it wet for 10–15 minutes. Don’t let it dry.
- Agitate with a deck brush to lift grime and algae.
4) Rinse at low pressure
- Hold the wand 8–12 inches from the surface, start off the deck, then sweep on in smooth, overlapping passes.
- Work with the grain, one or two boards at a time. Maintain a constant distance and speed to avoid lap marks.
- Feather edges and keep a wet edge so rinse lines don’t show.
5) Brighten and neutralize
- While the wood is clean and still damp, apply an oxalic acid brightener per label directions. Wait the recommended dwell time, then rinse thoroughly.
6) Dry, touch up, and finish
- Allow 24–48 hours of dry weather. High humidity or shade may require longer.
- Lightly sand raised grain or fuzzing with 80–100 grit. Vacuum or blow off dust.
- Apply stain or sealer per product instructions.
Safety tips
- Wear eye protection; high-pressure water can inject under skin. Keep hands and feet away from the spray.
- Never use a ladder with a pressure washer. Use extensions or clean from the ground.
- Pre-wet and post-rinse plants if using cleaners. Do not mix bleach with other chemicals.
- Avoid spraying up between board gaps or at rail post bases; it can drive water where it doesn’t dry well.
Special cases
- Composite decking: Many brands allow pressure washing up to 1500 PSI with a 40° tip at 8 in. distance. Use a mild soap and water; avoid harsh chemicals or rotary nozzles. Always check your manufacturer’s guidance to protect the warranty.
- Heavy mildew/algae: If oxygenated cleaner isn’t enough, you can spot-treat with a dilute bleach solution and a surfactant. Pre-wet plants and rinse thoroughly, and avoid prolonged contact with metal fasteners.
Example mildew mix (spot treatment)
- 1 part household bleach : 3 parts water + a few drops of dish soap
- Dwell time: 5–10 minutes, keep wet; rinse thoroughly
Common mistakes to avoid
- Too much pressure or the wrong nozzle: causes furred fibers and etched wood. Start with 40°, only step to 25° if needed.
- Holding the tip too close: creates stripes and gouges. Keep 8–12 inches away.
- Skipping cleaner and relying on water only: forces you to use higher pressure.
- Overlapping inconsistently: leaves lap marks. Maintain steady, overlapping passes.
- Not rinsing chemicals thoroughly: can cause blotching and finish adhesion issues.
- Sealing too soon: moisture trapped in wood leads to peeling. Let it dry fully.
Time and cost
- Time: 4–6 hours for 200–300 sq ft, plus 24–48 hours drying before finishing.
- Cost: Rent a washer for $40–90/day; buy an electric unit for $150–300 or gas for $300–600. Cleaner $15–25, brightener $15–25, sanding supplies $10–20.
Pro tips for better results
- Test in an inconspicuous area to dial in distance and speed.
- Clean in shade or on a cool day so chemicals don’t flash-dry.
- Keep the wand moving before pulling the trigger and release the trigger before stopping movement to prevent marks.
- Rinse from house outward so dirty water doesn’t splash back.
- After cleaning weathered gray wood, a brightener dramatically improves color and stain uptake.
When to call a professional
- Your deck is soft, splintering, or historically significant wood that’s easy to damage.
- You need to remove peeling paint or heavy solid-color stains (often requires chemical stripping and controlled rinsing).
- Multi-level or elevated decks where access and fall hazards complicate the work.
- You lack adequate water supply or are unsure how to control pressure safely.
Done right, pressure washing preps your deck for a longer-lasting finish without scarring the wood. Use the cleaner to do the heavy lifting, keep the pressure gentle, and finish with brightener and proper drying for the best outcome.