Short answer
Clean composite decking with warm soapy water and a soft or medium brush, scrubbing along the grain and rinsing well, and use a cleaner made for composite decking on stubborn marks. Whether you can pressure wash composite depends on the boards, so check the manufacturer's care guidance first; if it is allowed, use a low setting with a wide fan, well back from the surface.
How composite differs from timber
Composite boards are made from a mix of wood fibre and plastic, often with a protective outer layer. They do not need oiling or staining, and they do not rot in the same way as timber, but they still collect dirt, pollen and leaf debris, and green growth or mould spots can appear on the surface in damp, shaded spots.
Because the surface is engineered, the wrong cleaning method can scratch it, dull the finish or leave marks that will not come out. That is why the most important step is finding your board manufacturer's care guidance, which may also be tied to the warranty. If you do not know the make, check any paperwork from when the deck was fitted or ask the installer.
If your deck is timber rather than composite, our guide to cleaning decking covers the different approach that wood needs.
Everyday cleaning, step by step
- Clear the deck and sweep off leaves and loose dirt with a soft broom.
- Clear the gaps between the boards with a thin plastic scraper so water can drain and debris does not sit against the board edges.
- Mix warm water with a little mild detergent, or use a cleaner made for composite decking, following the label.
- Scrub along the grain or embossed pattern with a soft or medium brush. Avoid wire brushes and abrasive pads.
- Rinse thoroughly with a hose so no soapy residue dries on the surface.
- Let the deck dry and check for any marks that need extra attention.
Dealing with stubborn marks
Mould and algae spots tend to appear where the deck stays damp. Scrub them with a composite-safe cleaner and rinse well. If they come back quickly, look at why that area stays wet: overhanging plants, blocked gaps or a pot that sits in the same place all year.
Grease and food spills from a barbecue are easiest to remove while they are fresh. Blot up what you can, then wash with warm soapy water. Older grease marks may need a degreaser that the board manufacturer approves.
Leaf stains can appear when wet leaves are left lying on the boards, particularly from trees with dark leaves. Sweeping regularly in autumn prevents most of this. Existing marks often lighten with a suitable cleaner and gentle scrubbing, and some fade naturally over time in daylight.
Whatever the mark, test any product on an offcut or a hidden board first, never mix products, and avoid harsh solvents that could damage the surface.
Can you pressure wash composite decking?
Some manufacturers say a pressure washer can be used on their boards within certain limits, others advise against it, and using one in a way the guidance does not allow can scar the surface. Check first, and if you are unsure, stick with a brush and hose.
If pressure washing is permitted, choose a low setting and a wide fan nozzle, hold the lance well back, and keep it moving along the length of the boards. Try a hidden area first and look closely for any change in the surface before doing the rest of the deck. Never use a pinpoint or rotating nozzle on composite.
Keeping composite decking clean
A quick sweep and rinse every so often stops dirt bedding in. Move pots and furniture occasionally so damp patches do not form beneath them, use mats under barbecues, and keep the gaps clear so the boards dry after rain. In shaded gardens, trimming back plants that overhang the deck helps more than any cleaning product.
When to call a professional
It is worth calling a professional if marks have built up over a long time, if the deck is large or includes lots of steps, or if you want the work done without worrying about the board finish. Mention the make of the boards if you know it, so the method can follow the manufacturer's guidance.
We clean composite decking as well as timber. Tell us your boards are composite when you enquire, or send a photograph if you are unsure. The approach is agreed for your deck once we have seen it, and steps, edges and any adjacent patio can be included by agreement.
Rather have it done for you?
Timber and composite decking cleaned of green algae and slippery grime. Family-run by Jason and Lucas Prior, covering south Essex.
Frequently asked questions
Can you pressure wash composite decking?
It depends on the boards. Check the manufacturer's care guidance first. If it is allowed, use a low setting and a wide fan held well back, and test a hidden area before doing the whole deck.
What should I not use on composite decking?
Avoid wire brushes, abrasive pads, harsh solvents and any product the board manufacturer advises against, and never mix cleaning products. These can scratch or dull the surface.
How do I get black spots off composite decking?
Scrub them with a cleaner made for composite decking and rinse well. If they return, look for what keeps that area damp, such as blocked gaps or plants overhanging the boards.
Related guides
- How to clean decking: cleaning timber decking by hand or with a pressure washer, without roughening the boards or leaving them slippery.