How to Clean a Wood Deck

Clean a wood deck with a deck cleaner, a stiff brush, and a low-pressure rinse — and resist the temptation to blast it with a pressure washer. High pressure raises the grain and gouges the soft wood between the grain lines, leaving a fuzzy, furrowed surface that then needs sanding to fix. Sweep the boards and clear the gaps first, work a section at a time along the boards, let the deck dry fully, and save any resealing for a stretch of mild, dry weather. Done gently, the job restores the wood without damaging it.

Why high pressure is the wrong default

Wood is not concrete. Its surface is a mix of harder grain lines and softer wood in between, and a high-pressure stream cuts into that softer wood unevenly. The result is a raised, fuzzy grain and shallow furrows that look worse than the dirt you started with and usually need sanding to smooth out. Pressure can also drive water deep into the boards and force it under railings and flashing.

The gentler, more reliable approach is closer to soft-washing: let a deck cleaner loosen the grime and growth, do the mechanical work with a stiff brush, and rinse at low pressure. The same solution-first logic behind soft washing protects the wood while still getting it clean. If you do reach for a pressure washer, the cautions in the best time of year to pressure wash apply — use a wide fan tip, keep it moving, hold it well back, and always follow the direction of the boards.

What you need

• A dedicated deck cleaner suited to your problem — grime, gray weathering, or mildew
• A stiff-bristle scrub brush, ideally on a pole to save your back
• A putty knife or narrow tool for clearing the board gaps
• A garden hose for rinsing
• Water or drop-cloths to protect nearby plants

Cleaning the deck step by step

1. Clear and sweep. Remove furniture and planters, sweep off loose debris, and clear packed material from the gaps between boards with a putty knife. Debris in the gaps traps moisture against the board edges, which is exactly where rot begins.
2. Wet the plants and the deck. Soak surrounding vegetation with plain water so runoff is diluted, then lightly wet the deck so the cleaner spreads evenly.
3. Apply the deck cleaner and let it dwell. Work in manageable sections so the cleaner does not dry out before you scrub, and give it the dwell time on the label.
4. Scrub along the boards. Use the stiff brush in the direction of the grain, not across it. Let the cleaner and brush lift the gray, grime, and growth together.
5. Rinse at low pressure. Rinse each section thoroughly with the hose, again working with the boards, until the water runs clear.
6. Rinse the plants again and let the deck dry. Give the vegetation a final plain-water rinse, then let the deck dry fully before doing anything else to it.

Removing gray, mildew, and algae

Two problems account for most dirty decks. Gray weathering is sun-and-water damage to the surface fibers; a brightening deck cleaner restores much of the original color. Green film and black spotting are algae and mildew, which thrive on damp, shaded boards — these need a cleaner that kills the organism, not just a scrub, or they return within weeks. The principle mirrors cleaning wood decks and fences: match the cleaner to what you actually see, and treat living growth as something to kill at the source.

Whatever product you choose, test it on a hidden section first and follow the label on dilution, dwell time, and runoff.

Drying and resealing

Cleaning opens the door to resealing, but timing is everything. The wood must be thoroughly dry — often a couple of dry days, longer in humid weather — before you seal or stain, or the finish will not bond and can trap moisture in the boards. Plan the whole project around a stretch of mild, dry weather so the finish has time to cure. Rushing the sealer onto a still-damp deck is one of the most common ways a good cleaning job gets undone.

Common mistakes

• Blasting the deck with high pressure. Raises the grain and gouges the soft wood, creating work rather than saving it.
• Scrubbing across the boards. Work with the grain, not against it, to avoid scratching the surface.
• Skipping the gaps. Debris left between boards holds moisture and feeds rot.
• Scrubbing mildew without killing it. The green returns fast because the organism survived.
• Sealing too soon. A damp deck will not hold the finish and can trap moisture inside.

Keeping the deck in good shape

A deck stays cleaner and lasts longer when water drains and the boards dry between rains. Keep the gaps clear, sweep off leaves that hold moisture, improve airflow around shaded sections where you can, and fold a gentle annual cleaning into your seasonal routine with resealing every few years. Cleaned with a brush and a cleaner rather than brute force, a wood deck comes back bright without paying for it in raised grain and sanding.