17 August 2026 · Patios and Paths
How to clean decking boards without wrecking them
Decking looks fantastic when it's new. Give it a couple of Lincolnshire winters, though, and most timber boards turn a dull pewter-grey, grow a slick layer of green algae, and start to feel more like a skating rink than a place to sit with a coffee. Knowing how to clean decking boards properly makes the difference between a surface that scrubs up like new and one that ends up splintered, raised-grain, and worse than before you started.
The short answer: work with the wood, not against it. Low pressure, the right cleaner, and brushing along the grain — not across it.
Why decking gets into such a bad state
Timber decking sits outdoors, horizontal, and slightly damp for much of the year. That's a perfect recipe for algae, mould, and the UV greyness that comes from the sun breaking down surface lignin. North-facing decks — common in gardens around Skellingthorpe and Saxilby where properties back onto open fields — rarely dry out fully between October and March, so green algae builds up season after season.
The result is a surface that's slippery underfoot, looks neglected, and slowly rots if the moisture is never cleared away. Cleaning removes the biological growth, opens up the wood grain, and lets you see what you're actually working with.
What you'll need before you start
Gather everything before you begin — stopping halfway to search for something means cleaners dry unevenly and leave tide marks.
- A stiff-bristle deck brush (not a wire brush — that scratches and raises grain)
- A specialist wood or decking cleaner (diluted oxalic acid or a purpose-made product)
- A garden hose or low-pressure washer (below 1,000 psi if possible)
- Safety gloves and old clothes
- A plastic scraper for stubborn debris between boards
- Filler sticks or exterior wood filler if you spot cracked boards
Avoid household bleach as your main cleaner. It strips colour unevenly and kills off nothing below the surface, so the algae comes straight back within weeks.
How to clean decking boards step by step
- Clear the deck completely. Move furniture, plant pots, and mats. Algae hides under anything left sitting on the boards.
- Sweep off loose debris. Leaves, pine needles, and general garden muck trap moisture — get rid of them first.
- Apply your decking cleaner. Follow the dilution instructions on the label. Work in sections so the product doesn't dry before you scrub.
- Scrub along the grain. This is the single most important rule. Brushing across the grain raises and splits the fibres, leaving a rough surface that harbours more dirt next time. Always brush in the direction the boards run.
- Rinse thoroughly. Use a garden hose or a wide-fan pressure washer nozzle from a sensible distance — at least 30 cm from the surface. Work along the boards, not across them.
- Allow to dry completely. At least 48 hours in warm weather, longer if the weather is damp. Wood must be dry before any oil or treatment goes on.
Getting rid of stubborn green algae and black mould
If a general clean isn't shifting the worst of the green, a second pass with a slightly stronger solution — or a dwell time of 15–20 minutes before scrubbing — usually does it. Black mould spots between boards can be worked with a narrow brush or an old toothbrush to get into the gap properly.
For decks that have been neglected for several years, like many we see in Nettleham and Welton where decking was installed with the house and never properly maintained, a professional clean is often more effective than a DIY attempt. The right equipment applies even pressure across every board without the risk of over-washing one patch and missing another.
What about a pressure washer?
Pressure washing decking is possible, but the margin for error is small. Too close and you raise the grain badly, leaving a fluffy surface that's even harder to keep clean. Too powerful and you can split older boards outright. If you're using a domestic pressure washer, fit a wide-fan nozzle, keep the lance moving constantly, and stay back further than you think you need to.
Our decking cleaning guide covers restoration and oiling in more detail if you want to go deeper.
Should you sand the boards after cleaning?
If the wood grain has been raised by previous cleaning or weathering, a light sand along the grain once the deck is completely dry brings the surface back to smooth. Use 80–120 grit sandpaper and always go with the grain. Wipe away all dust before any treatment goes on.
Treating and protecting the wood after cleaning
A clean deck is the starting point, not the finish line. Once the boards are dry, applying a quality decking oil or stain fills the grain, repels moisture, and dramatically slows the return of algae and greyness. You'll need to reapply every 1–2 years depending on exposure and foot traffic.
Skip the treatment and the boards will grey again within a season. Do it properly and a deck can look good for a decade before major work is needed.
When it makes sense to call a professional
If your decking is heavily algae-covered, has been neglected for three or more years, or you're not confident about pressure settings and cleaner concentrations, a professional clean is usually better value than the risk of damage. We work across Lincolnshire — from Lincoln city centre to villages like Bracebridge Heath and Heighington — and we see the results of well-intentioned DIY cleaning that's gone wrong regularly.
We use commercial-grade equipment calibrated for timber, apply the right dwell times for the condition of the wood, and leave boards ready to oil rather than needing sanding back before treatment can even begin. You can see the full range of surfaces we cover on our services page or check whether we cover your area on the Lincolnshire areas page.
If your deck needs attention this season, get a free quote today — we'll assess the boards and give you an honest answer about what's achievable.
Frequently asked questions
Can I use a pressure washer to clean decking boards?
Yes, but keep the pressure below 1,000 psi, use a wide-fan nozzle, and always work along the grain of the wood. Too much pressure or the wrong angle will raise the grain and leave the surface rough and harder to keep clean.
How often should decking boards be cleaned?
Once a year is a good baseline for most gardens — ideally in spring before the surface gets heavy use. Shaded or north-facing decks may need cleaning twice a year as they stay damp longer and algae builds up faster.
Why do my decking boards keep going green so quickly after cleaning?
Green algae returns fast if the deck stays damp, sits in shade, or wasn't treated with a protective oil or stain after cleaning. Treatment fills the wood grain and slows biological growth significantly.
Is it better to clean decking boards yourself or hire a professional?
For lightly soiled, well-maintained decking, a careful DIY clean is fine. For heavily neglected, algae-covered, or delicate older boards, professional cleaning reduces the risk of raising the grain or splitting boards, and produces a more even result.
Need a hand with yours? We cover Lincolnshire for patios, driveways, paths and more — see the areas we cover or browse our services. Get a free quote or call 07874 010739.
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