Composite decking is marketed as low-maintenance, and it broadly is, but low-maintenance doesn't mean no-maintenance, and cleaning it the wrong way can scratch, dull, or discolour the surface in ways that are hard to reverse. Getting it right means sticking closer to manufacturer guidance than to whatever's fastest with a jet washer.
This guide covers the manufacturer-safe cleaning methods most composite decking brands recommend, and the common mistakes that cause lasting damage.
What composite decking actually is
Composite decking is a mix of wood fibre and recycled plastic, capped in most modern products with a protective outer layer that resists fading, staining and moisture better than timber alone. That capped layer is also what's most vulnerable to scratching from abrasive cleaning or damage from excessive heat and pressure. Older, uncapped composite boards, more common on installations from a decade or more ago, are generally more porous and stain-prone, and often need slightly gentler treatment still.
Different brands specify slightly different care instructions, so checking your specific manufacturer's guidance is genuinely worth the five minutes before your first deep clean, particularly regarding maximum safe pressure washer settings, since ranges do vary noticeably between manufacturers.
The safe cleaning method
Sweep loose debris first, then wash with warm water and a mild soap or dedicated composite decking cleaner, using a soft-bristle brush, ideally with synthetic rather than stiff wire or hard nylon bristles, working along the grain of the boards. Rinse thoroughly with a hose or low-pressure spray, checking gaps between boards for trapped leaves and debris as you go, since these collect moisture and can encourage mould growth if left.
If using a pressure washer, most manufacturers cap safe pressure well below what's fine for timber decking, often around 1,200-1,500 psi maximum with a wide fan nozzle held at a reasonable distance and kept moving, never held static on one spot. Testing on a small, inconspicuous section first is a sensible habit before working across the whole deck.
Common mistakes that cause damage
Using a narrow turbo nozzle or holding the jet too close is the single most common cause of composite decking damage, gouging or fuzzing the capped surface layer in a way that can't be sanded out the way it could on timber. Wire brushes and abrasive scourers cause similar surface damage, and are best avoided entirely.
Oil-based cleaning products or those not specifically approved for composite decking can sometimes leave residue that attracts more dirt, or in some cases interact poorly with the capping material, which is why sticking to manufacturer-approved or genuinely mild soap-based products matters more here than on natural timber. When in doubt, a small test patch in an inconspicuous corner is a sensible precaution before treating the whole deck.
Costs and when to call a professional
DIY cleaning with mild soap and a soft brush costs very little and is entirely reasonable for regular maintenance. Professional composite decking cleaning, useful for a deeper seasonal clean or algae removal in shaded, damp corners, typically costs around £4-£7 per square metre, with pressure kept safely within manufacturer limits.
It's also worth checking your specific manufacturer's warranty document before any professional clean, since some composite decking brands ask for evidence that approved cleaning methods and pressure limits were followed if a warranty claim is ever needed later, and a professional using the wrong technique could complicate that if something did go wrong down the line.
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