How to Clean a Wood Fence: Oxygen Bleach, Low Pressure, and 2 Dry Days Before Stain

Short answer: wet the fence, apply an oxygen bleach cleaner (sodium percarbonate) mixed with warm water as the label says, let it work for the time on the label without drying, scrub with a soft brush, then rinse with a garden hose or a pressure washer on a low setting: about 500 to 800 PSI on cedar, with a 25 or 40 degree fan tip held about 12 inches from the wood. Do not use chlorine bleach. If you plan to stain, let the fence dry 48 hours first.

Cleaning is the cheapest thing you can do to make a fence last, and it is the first step before any new coat of stain. We build cedar privacy fences around Portland, and this is the method that cleans cedar without chewing it up.

The steps at a glance

What is the best cleaner for a wood fence?

Oxygen bleach. It is sold as a powder (sodium percarbonate) or as a ready-made deck and fence cleaner. It kills mildew and algae and lifts the gray layer off the surface without breaking down the wood, and it breaks down into oxygen and soda ash, so it is far easier on plants than chlorine bleach. The Western Red Cedar Lumber Association names oxygen bleach as its preferred mildew cleaner. For plain dirt with no mildew, a mild non-phosphate detergent and water is often enough.

Can you use chlorine bleach on a wood fence?

You should not. Chlorine bleach kills mildew, but it breaks down lignin, the natural glue that holds wood fibers together. That leaves the surface fuzzy and weak, strips the natural color out of cedar, and makes it harder for stain to bond. It is also hard on the plants along the fence line.

Should you pressure wash a wood fence?

You can, carefully. Cedar is a soft wood, and a pressure washer turned up high will cut grooves into it and raise the fibers into a fuzzy surface. Keep it to about 500 to 800 PSI on cedar, use a 25 or 40 degree fan tip, never the narrow red or yellow tips, hold the wand about 12 inches from the boards and work in long strokes with the grain. Let the cleaner do the work, the water only rinses it off.

If a spot will not come clean at low pressure, scrub it and rinse again rather than moving the wand closer. Gouges from a pressure washer are permanent.

How do you get green algae and moss off a fence?

The same oxygen bleach cleaner kills algae. Let it sit, scrub the green areas with a soft brush, then rinse. In Portland the green shows up first on the shaded north side of a fence, under trees, and along the bottom boards where sprinklers hit. Those spots need cleaning more often than the sunny side.

How do you remove black stains and rust streaks?

With an oxalic acid wood brightener, after cleaning. Oxalic acid is what removes water, tannin and iron stains on cedar, including the black streaks that run down from rusting nails. Handle it carefully and follow the label. The long-term fix for rust streaks is fasteners that do not rust, which is why we build every cedar fence with stainless steel fasteners.

When is the best time to clean a fence in Portland?

Late spring through summer. The fence needs to dry after a wash, and if you are staining it, it needs dry days on both sides of the stain too. Around Portland that window is really June through September.

We wrote the full month-by-month calendar in how long stain needs to dry before rain.

How long should a fence dry after cleaning before you stain it?

Plan on 48 hours of dry weather, and longer on the shaded side. The real test is a moisture meter reading under 12 percent, or the water test: sprinkle a few drops on a board, and if they soak in within a minute, it is ready.

Cleaning is step two of seven in our guide on staining a fence the right way.

Frequently Asked Questions

How often should you clean a wood fence?

Whenever you see green or gray building up, and always before a new coat of stain. In Portland that usually means the shaded side needs it more often than the sunny side.

Can I clean a fence with just soap and water?

For light dirt, yes. A mild non-phosphate detergent and a soft brush is enough. For mildew, algae or a gray surface, use an oxygen bleach cleaner.

What PSI should I use to pressure wash a cedar fence?

About 500 to 800 PSI, with a 25 or 40 degree tip held about 12 inches off the wood. Higher pressure gouges cedar and raises the grain.

Will cleaning a fence remove the old stain?

A cleaner alone usually does not. Removing old stain takes a stain stripper, and that is a different job from cleaning.

Is vinegar good for cleaning a wood fence?

It is not what the wood and finish makers recommend. Use an oxygen bleach cleaner for mildew and an oxalic acid brightener for stains.

Cleaning on a schedule is one of the things that decides how long a wood fence lasts.

Gorilla Works proudly serves Portland, Gresham, Beaverton, Hillsboro, Tigard, Lake Oswego, Happy Valley, Milwaukie, Troutdale, Vancouver WA, and Camas WA. Call (971) 343-4964 or request a fence quote.