Cleaning Wood Decks and Fences

Clean wood decks and fences with low pressure and a wood-safe cleaner, not brute force. High pressure raises the grain, gouges soft wood and shortens the life of the boards. Think of the wash as the prep step before resealing, because the sealer, not the cleaning, is what actually keeps water out of the wood.

Why high pressure is the wrong tool for wood

Wood is soft, and outdoor wood is softer than it looks. Cedar, redwood, pine and pressure-treated lumber all have a grain structure that a concentrated jet of water can tear apart. Hold a narrow tip too close and you will literally carve grooves into the boards, leaving a washboard texture that never fully smooths out.

Even when the damage is not obvious, high pressure raises the grain — it lifts and separates the wood fibers so the surface dries fuzzy and rough. That roughness holds dirt and moisture more readily than a smooth board, so an aggressive cleaning can leave the wood in worse shape than before. Driving water deep into the grain also slows drying and can encourage rot in the very spots you were trying to clean.

This is a general truth about a lot of home exteriors, not just decks. Our overview of what not to pressure wash covers the other surfaces — siding, stucco, mortar, roofing — where the same logic applies. Wood belongs firmly on that list.

The low-pressure method that actually works

The goal is to let the cleaner break down grime and organic growth, then rinse it away gently. Pressure is a rinsing aid, not the main event.

Step by step

1. Clear and protect. Sweep the deck, move furniture and planters, and wet down nearby shrubs and grass before you start. Cover or shield plants you cannot move so cleaner runoff does not settle on the foliage.
2. Wet the wood. Dampen the boards with plain water first. Dry wood absorbs cleaner unevenly and can end up streaky.
3. Apply a wood-safe cleaner. Use a dedicated deck or wood cleaner mixed to the label. Oxygenated (sodium percarbonate) cleaners lift graying and mildew without the harshness of chlorine bleach. Work in shade if you can, so the solution does not dry before it does its job.
4. Let it dwell, then agitate. Give the cleaner the time the label specifies, usually several minutes, then scrub with a stiff-but-not-metal brush, working with the grain along the length of the boards.
5. Rinse at low pressure. If you use a pressure washer, fit a wide fan tip (40 degrees or a soft-wash tip), keep it well back, and keep the wand moving with the grain. A garden hose with a spray nozzle is often enough. For more on choosing the right spray pattern, see our nozzles and tips guide.
6. Let it dry fully. Give the wood a couple of dry days before you assess whether it needs sealing.

Choosing a cleaner

Cleaner type	Best for	Watch out for
Oxygenated (percarbonate)	General graying, mildew, light stains	Still needs rinsing; follow dwell time
Wood-specific deck cleaner	Prep before sealing or staining	Match to species; test first
Mild soap and water	Light dirt, routine upkeep	Weak on mildew and deep graying
Chlorine bleach	Rarely recommended for wood	Corrodes fasteners, can fuzz grain, harms plants
Brighteners (oxalic-acid based)	Restoring color after cleaning	Acidic; wear protection, protect plants

Cleaning is the prep step for resealing

Here is the part homeowners often miss: cleaning a deck does not protect it. A clean, bare deck is actually more exposed than a dirty one, because the wash removes both the grime and whatever old, failing finish was still clinging on. What protects wood from water is the sealer or stain sitting on top.

So treat cleaning as stage one of a two-stage job. Once the wood is clean and fully dry, check whether water still beads on the surface. If drops soak straight in, the finish is gone and the wood is ready to reseal. Sealing traps that clean surface under a fresh water-repellent layer, and that is what buys you years instead of months.

Timing matters. Seal too soon, while the boards are still damp inside, and you trap moisture under the finish, which leads to peeling and cloudiness. Most products want two to three dry days after cleaning and a moisture level below their stated threshold. Check the label, and pick a dry stretch of weather for the whole sequence.

Common mistakes

• Using a narrow, high-pressure tip. The single fastest way to permanently scar a deck. Wide fan or soft-wash tips only.
• Holding the wand too close. Even a wide tip gouges up close. Keep distance and keep moving.
• Skipping the cleaner and relying on pressure. Pressure without a cleaner just blasts the surface; the cleaner does the real work.
• Letting cleaner dry on the wood. Dried solution streaks and can lighten the wood unevenly. Work in shade and rinse before it dries.
• Reaching for straight bleach. It corrodes fasteners, can fuzz the grain and kills plants in the runoff.
• Cleaning and then walking away. A bare, unsealed deck is left exposed. Cleaning without resealing skips the step that actually protects the wood.
• Ignoring the plants. Wet foliage before and after, and shield what you cannot move, so runoff does not scorch your beds.
• Sealing over damp wood. Traps moisture and guarantees a peeling finish. Wait for the wood to dry through.

The short version

Go gentle. A wood-safe cleaner and a light touch will lift years of gray and mildew without tearing up the boards, and the wash sets you up for the reseal that actually keeps water out. If your deck is two stories up or the work means leaning off a ladder, that is a job worth handing to a professional rather than risking a fall.