How to clean a composite decking properly

Composite decking is one of the most popular choices for gardens across Lincolnshire right now — low maintenance, long-lasting, and genuinely smart-looking when it's clean. But knowing how to clean composite decking properly matters more than most people realise. Use the wrong method and you can strip the protective coating, leave permanent streaks, or force water into the board joints. Get it right and it looks nearly new again.

Here's everything you need to know, from a quick weekly sweep to a proper annual clean.

Why composite decking still needs regular cleaning

Manufacturers often market composite boards as "virtually maintenance-free." That's true compared to timber — but it doesn't mean you can ignore it. Algae, green mould, leaf tannins, and pollen all settle into the textured surface of composite boards over time, especially in shadier gardens or anywhere near trees.

Left long enough, that green film becomes genuinely slippery. It can also stain the boards permanently if it's worked into the grain by foot traffic or wet weather over a full winter. In places like Nettleham or Washingborough where gardens back onto open fields, decking tends to pick up windblown organic matter faster than you'd expect.

What you'll need before you start

Having the right kit ready saves time and reduces the risk of damage:

• A stiff-bristled deck brush (not wire — wire scratches the surface)
• A garden hose or low-pressure setting on a pressure washer
• A composite-safe decking cleaner (check the label — avoid anything with bleach or solvents unless specified as composite-safe)
• A bucket of warm water
• Soft cloths or a sponge for spot treatment

Avoid harsh domestic cleaners, neat bleach, and high-pressure settings. These are the three things most likely to damage composite boards.

How to clean composite decking properly: step by step

1. Clear the deck completely. Move furniture, plant pots, and anything else sitting on the surface. Standing water under pots is a common cause of localised staining.
2. Sweep off loose debris. Get rid of leaves, grit, and dirt with a stiff brush before introducing any water — washing debris into the board joints causes long-term problems.
3. Rinse with a hose or low-pressure washer. Work along the length of the boards, not across them. A fan-tip nozzle at around 1,200–1,500 PSI is fine. Keep the lance at least 30 cm from the surface and avoid holding it still in one spot.
4. Apply your composite cleaner. Follow the product instructions — most ask you to leave it for five to ten minutes. Don't let it dry on the surface.
5. Scrub along the grain. Use your deck brush in the direction of the board texture. This lifts the algae and dirt out of the grooves rather than pushing it deeper in.
6. Rinse thoroughly. Make sure all the cleaning solution is gone before it dries. Residue left behind can leave a white film.
7. Check the joints. Use a blunt tool or a piece of thin card to clear any debris from between boards — clogged joints trap moisture and are where mould tends to start.

Dealing with stubborn stains on composite boards

Green algae and mould

This is the most common problem and usually lifts well with a proper composite cleaner and a good scrub. If it's been left for a season or more, you may need two passes. A mould-specific composite treatment applied the evening before can also help loosen it.

Tannin stains from leaves

Oak and sycamore leaves are the worst offenders — they leave dark brown or black marks that look alarming but usually respond well to a targeted composite stain remover. Treat as soon as you notice them rather than leaving them over winter.

Oil and grease spots

BBQ grease is common. Dab it with a composite-safe degreaser and work it in gently with a cloth before rinsing. Don't scrub aggressively on a fresh oil stain — you'll just spread it.

Can you pressure wash composite decking?

Yes — but carefully. Pressure washing is one of the most effective ways to clean composite decking quickly, as long as you use a fan nozzle, keep the pressure below 1,500 PSI, and always move along the board rather than across it. A rotary (turbo) nozzle is too aggressive for most composite surfaces.

If you're not confident about pressure, err on the side of lower — a good brush and the right cleaner will do most of the work. Our decking cleaning guides cover more on safe pressure-washing techniques for different surfaces.

How often should you clean composite decking?

• Every few weeks: a quick sweep and rinse to stop debris building up
• Every spring: a proper full clean before the garden season starts
• Every autumn: clear it down before winter sets in, especially if trees overhang

Decking in full shade, or backing onto fields and hedges — common across villages like Heighington, Branston, and Saxilby — will need attention more often because it stays damp longer.

When it makes sense to call in a professional

If the algae is well established, the boards have deep staining, or you're not comfortable using a pressure washer safely, a professional clean is often the better call. We work on composite decking across Lincolnshire and regularly restore boards that homeowners assumed were beyond saving.

You can see the full range of surfaces we cover on our services page or find out whether we cover your area on our areas page.

A professional clean typically takes a couple of hours and leaves your decking looking genuinely fresh — not just slightly less grimy.

Ready to get your decking looking its best?

If you'd like us to take it on, we're happy to come out, take a look, and give you a straightforward quote. No obligation. Request a free quote and we'll be in touch quickly.

Frequently asked questions

---

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.