How to Clean a Wood Fence Without a Pressure Washer

A pressure washer cleans a fence by force, and force is the problem. Too close or too narrow a tip and it cuts the soft earlywood between the growth rings, leaving a furred, grooved surface that takes stain unevenly and weathers faster. Cedar, the most common premium fence wood, is soft enough to damage at pressures a homeowner machine reaches easily.

The alternative is to let chemistry do the work and use water only to rinse. A hose, a pump sprayer and a brush clean as well as a pressure washer on most fences — they just need the right cleaner for what is actually on the wood, and ten minutes of patience while it works.

Most cleaning advice gives one recipe for every fence. But “dirty” covers at least five different things, and two of them do not respond to bleach of any kind. Match what you see before you buy anything.

Two checks settle the ambiguous cases. Scrape a grey board lightly with a fingernail or putty knife: if bright wood shows just under the surface, it is weathering, not a coating. And look at where black marks sit: speckles spread across a board are mildew, but streaks that start at a fastener and run downward are iron stains, however much they look like mould.

Oxygen bleach is the default for a reason. It is sold as a powder — sodium percarbonate, the active ingredient in most “oxygen” laundry boosters and many deck and fence cleaners — and when it dissolves in warm water it releases hydrogen peroxide that lifts grey fibres, algae and mildew without bleaching the wood white. It is also alkaline, which is why a brightener often follows: the acid neutralises what is left and brings back the wood's colour.

Chlorine bleach is the one to avoid as a general cleaner. It kills mildew on contact, but it also attacks lignin, the glue that holds wood fibres together, so the surface goes pale and fuzzy. And the diluted runoff harms grass and shrubs along the fence line.

Mixing ratios are common practice for these products; the label of the product you buy takes priority. Never combine chlorine bleach with ammonia or acid cleaners.

• Garden hose with an adjustable nozzle — a fan or shower setting, not a jet.
• Pump sprayer, 1 to 2 gallons, with a nozzle you can open to a coarse spray.
• Stiff synthetic-bristle brush on an extension pole. Not wire — see mistakes, below.
• Buckets for mixing, and warm water so the powder dissolves.
• Rubber gloves and eye protection. Both cleaners and brighteners splash.
• Plastic sheeting or old sheets for delicate plants, if the bed runs right up to the fence.

Work in sections of about 10 to 15 feet, and pick an overcast day or the shaded side first. Cleaner that dries on the wood in hot sun stops working and leaves blotches.

1. Wet everything

Soak the fence section and the plants and grass along its base with plain water. Wet wood absorbs less cleaner into the surface, so it stays where it is needed, and wet leaves resist whatever drips onto them.

2. Mix and apply the cleaner, bottom up

Dissolve the oxygen bleach in warm water at 4 ounces per gallon for a lightly weathered fence or up to 8 ounces for a heavily grey or green one, and use it within a few hours — it loses strength once mixed. Spray from the bottom of the boards upward. Working upward stops cleaner running down over dry wood below and leaving clean streaks.

3. Let it work, and keep it wet

Give it 10 to 15 minutes. You should see a faint foaming and the grey or green begin to lighten. If any area starts drying, mist it with more cleaner rather than water. This wait is the part that replaces the pressure washer, so do not rush it.

4. Scrub with the grain

Brush firmly along the grain, not across it. The brush breaks up the loosened layer; it should not need hard pressure. Pay extra attention to the bottom 12 inches, where splash-back and algae collect, and to the top rail.

5. Rinse from the top down

Rinse thoroughly with the hose, top to bottom, until the runoff is clear. Then rinse the plants at the base again.

6. Brighten, if the wood is still grey or has black streaks

Apply an oxalic acid brightener while the wood is still damp, following its label, leave it 5 to 15 minutes and rinse again. On cedar and redwood this step is usually what brings the warm colour back, and it is the only one that removes iron streaks.

7. Let it dry

Leave the fence at least 48 hours in dry weather before staining or sealing. The water-drop test in the section below tells you when it is really ready.

Oxygen bleach is the gentlest of the effective cleaners, but a strong mix is still alkaline enough to burn soft leaves if it sits on them. The routine that works: soak the plants first, cover anything delicate with sheeting (lifted off again within the hour so it does not cook underneath), and rinse the whole bed when you rinse the fence. Chlorine bleach runoff is the one to take seriously — it will brown a strip of lawn along the fence line.

A 6-foot privacy fence has about 6 square feet of face per linear foot, per side. Oxygen bleach powder is usually sold by the pound, and 1 pound is 16 ounces:

How far a gallon goes depends on how thirsty the wood is — rough-sawn and weathered boards soak up far more than smooth ones. Mix a gallon, clean one measured section, and scale from what that used. It is cheaper than guessing, and fresh batches work better than one big one left standing.

• A wire brush on cedar or redwood. Steel bristles leave tiny particles in the grain that react with the tannins and turn into black specks within weeks. Use synthetic bristles, or bronze if you must.
• Letting cleaner dry on the wood. It stops working and leaves a blotchy, lap-marked surface. Smaller sections, shade, and a mister fix this.
• Using bleach on black streaks. If they start at nails, they are iron stains. Oxalic acid removes them; bleach does not, however long you scrub.
• Scrubbing across the grain. It raises fibres and leaves swirl marks that show through stain.
• Staining the same day. Wet wood cannot absorb stain, so it sits on top and peels.

A clean fence is the moment to finish it, because the wood is as receptive as it will ever be. Sprinkle water on a few boards on the shaded side after two dry days. If it darkens and soaks in within a minute, the fence is ready; if it beads on the surface, wait.

Whether to finish it at all depends on the wood — worthwhile on pressure-treated pine, mostly cosmetic on cedar — and should you stain your fence→ covers that decision. For cedar specifically, the product choice and quantities are in how to seal a cedar fence→.

If cleaning turned up soft boards, loose pickets or a leaning section, the wood is past a cosmetic fix — see fence repair cost→.