The short answer
Composite decking is cleaned with warm soapy water and a soft brush — it needs no oiling, staining or sealing. For routine cleaning, sweep off debris, then scrub the boards with warm water and a mild soap or composite deck cleaner, working along the grain of the board, and rinse thoroughly. Clear the gaps between boards so water and dirt drain away. Mould, algae and stains are tackled with a suitable deck cleaner; oily or food stains are best dealt with quickly. Pressure washers can be used but with care — keep them on a low setting at a safe distance, as too much pressure or a too-close nozzle can damage the surface and may affect the warranty. Always check the manufacturer's care guide.
Low-maintenance does not mean no-maintenance. Composite still needs regular cleaning to look its best — here is the simple routine and how to deal with stains and mould safely.
Cleaning composite
- Routine cleanWarm soapy water + soft brush
- FrequencyPeriodically; more if shaded/damp
- Mould & algaeSuitable deck cleaner
- Pressure washerLow setting, safe distance, with care
- Never needsOiling, staining or sealing
The routine clean
Most composite decking is kept clean with a straightforward routine that needs no special equipment:
- Sweep first: remove leaves, dirt and debris, and clear the gaps between the boards so water and dirt can drain. Debris trapped in the gaps holds moisture and encourages mould.
- Wash with warm soapy water: use warm water with a mild soap or a dedicated composite deck cleaner, and a soft-bristled brush. Scrub along the length of the boards (with the grain) rather than across.
- Rinse thoroughly: rinse the soap and loosened dirt off with clean water so no residue is left behind.
How often depends on the deck. A sheltered, sunny deck may only need an occasional clean, while a shaded, damp or tree-overhung deck needs cleaning more regularly to keep mould and algae at bay. Cleaning a couple of times a year, with extra attention in autumn when leaves fall, suits most decks.
Mould, algae and green growth
Composite resists rot, but in damp, shaded UK conditions a thin film of mould or green algae can still grow on the surface, fed by trapped dirt, pollen and leaf debris rather than the board itself. It is a surface issue, not decay, and it is dealt with by cleaning.
To remove it, clear and sweep the deck, then wash with warm soapy water or a cleaner suited to composite decking, scrubbing the affected areas with a soft brush and rinsing well. Keeping the board gaps clear and the deck swept is the best prevention, because mould thrives where damp and debris collect. Improving airflow and light around the deck, and clearing fallen leaves promptly, all reduce green growth. Avoid harsh or abrasive cleaning that could damage the board surface.
Stains and spills
Most composite decking, especially capped composite, resists staining well, but spills are best dealt with promptly:
- Food and drink spills: rinse off and clean with warm soapy water as soon as possible.
- Grease and oil (from a barbecue, for example): clean quickly before it sets; a degreasing deck cleaner suited to composite helps. Using a mat under a barbecue prevents the problem.
- Ground-in dirt: warm soapy water and a soft brush usually lift it; a composite-specific cleaner handles stubborn marks.
Because cleaning methods and approved products vary between brands, the manufacturer's care guide is the authority on what to use on a particular board — some cleaners and chemicals are not recommended and could affect the appearance or the warranty.
Pressure washing and protecting the warranty
A pressure washer can be used on composite decking, but it must be used carefully. Too much pressure, or holding the nozzle too close, can damage the surface or the protective cap on capped composite, and in some cases this can affect the manufacturer's warranty. If you do use one:
- Use a low pressure setting and a wide fan nozzle, not a narrow high-pressure jet.
- Keep the nozzle a safe distance from the boards.
- Work along the length of the boards, with the grain.
- Follow the maximum pressure and distance stated in the manufacturer's care guide.
For most routine cleaning, warm soapy water and a soft brush do the job without any of that risk, which is why they are the recommended default. The overarching point is that composite is genuinely low-maintenance — it never needs oiling, staining or sealing like timber — but a periodic clean, clear board gaps, and care with pressure washing keep it looking good and protect both its appearance and its warranty.
A simple cleaning routine through the year
Rather than one big annual clean, composite decking is easiest to keep on top of with light, regular attention spread across the year. The deck stays cleaner, mould gets no chance to establish, and the work never becomes a chore:
- Through the year: sweep off leaves and debris regularly, and clear the gaps so water keeps draining. This little-and-often habit prevents most problems.
- Spring: give the deck a thorough wash with warm soapy water or a composite cleaner to clear off any winter grime and green growth, ready for the season of use.
- Summer: wipe up barbecue grease and food or drink spills promptly so they do not set, and keep furniture pads in place to avoid scratches.
- Autumn: stay ahead of falling leaves — leaf litter left in the gaps traps damp and is the main feed for mould over winter.
The single most useful habit is keeping the gaps between boards clear, because that is where damp and debris collect and where surface problems begin. A deck that is swept and drains freely needs only an occasional proper wash to stay in good condition.
Common cleaning mistakes to avoid
Composite is forgiving, but a few cleaning mistakes can mark or damage it — most of them from being too aggressive or using the wrong product:
- Harsh or abrasive cleaning: wire brushes, scouring pads and aggressive scrubbing can scratch the surface or the protective cap. Use a soft-bristled brush.
- The wrong chemicals: strong solvents, bleach or cleaners not recommended for composite can discolour or damage the board and may affect the warranty. Stick to mild soap or a composite-safe cleaner, and check the care guide.
- Pressure washing too close or too hard: a narrow high-pressure jet held near the surface is the classic way to damage composite — keep it low, wide and at a distance.
- Leaving spills and debris: letting grease set or leaves rot in the gaps makes cleaning far harder later and can cause staining.
- Trying to oil or stain it: composite does not need a finish, and coatings do not bond well — cleaning, not coating, is the answer to a dull-looking composite deck.
In short, composite cleaning is deliberately simple: warm soapy water, a soft brush, clear gaps and prompt attention to spills, with the manufacturer's care guide as the final word on products and pressure washing. Avoid the harsh-and-aggressive trap and the deck stays looking good for years with very little effort. Compared with the regular oiling and re-staining a timber deck demands, this occasional gentle clean is a small price for the durable, low-maintenance surface composite is chosen for.
Frequently asked questions
Can you pressure wash composite decking?
Yes, but with care. Use a low pressure setting and a wide nozzle, keep it a safe distance from the boards, and work along the grain. Too much pressure or a too-close nozzle can damage the surface or the protective cap and may affect the warranty, so check the manufacturer's care guide. For routine cleaning, warm soapy water and a soft brush are safer.
How do you get mould off composite decking?
Sweep and clear the deck, including the gaps between boards, then wash with warm soapy water or a cleaner suited to composite, scrubbing the affected areas with a soft brush and rinsing well. Mould on composite is a surface issue, not decay. Keeping the gaps clear, sweeping regularly and improving airflow help prevent it returning.
Do you need to seal or oil composite decking?
No. Composite decking does not need oiling, staining or sealing the way timber does — that is one of its main advantages. It only needs periodic cleaning with warm soapy water and a soft brush, plus prompt attention to stains and mould. Always follow the manufacturer's care guide for approved cleaning products.
Sources & further reading
- Trex — composite decking cleaning and care guide
- Checkatrade — composite decking care and cost guide
- RHS — paths, patios and decking
Figures on this page are typical UK ranges drawn from published sources and depend on your specific garden. They are guidance, not a quotation.