Short answer
Sweep it, then scrub along the grain with warm water, a little washing-up liquid and a soft brush, and rinse. Do it in spring and autumn, and deal with grease and leaf stains as soon as you see them. Avoid wire brushes, bleach and holding a pressure washer close to the boards.
In this guide
Composite decking is low maintenance, not no maintenance. A capped deck needs a proper clean twice a year and a quick sweep when leaves fall. Done regularly, that keeps it looking new and, more importantly, keeps it from getting slippery.
What you need
- A stiff broom
- A soft or medium bristle deck brush, not a wire brush
- A bucket of warm water with a squirt of washing-up liquid
- A garden hose
- For stubborn stains: a composite deck cleaner recommended by the board maker
The twice-a-year routine
Do this in spring, before the deck gets busy, and in late autumn once the leaves are down.
- Clear the deck. Move furniture, planters and mats. Mats trap moisture and can leave pale marks.
- Sweep thoroughly, including between the boards. A thin putty knife or a deck gap cleaner clears packed leaves from the gaps, which matters for drainage.
- Rinse with the hose to loosen dirt.
- Scrub along the grain with warm soapy water and a soft brush, a few boards at a time.
- Rinse well, so no soap film is left to attract dirt.
- Let it dry before putting the furniture back.
On a typical 15 m² deck this takes about an hour.
Green algae and moss
Shady decks, and those under trees, grow a green film in the grooves, especially through a damp Yorkshire winter. On capped boards it sits on the surface and scrubs off. If soapy water is not enough, use a deck cleaner made for composite, following the instructions. Don’t use bleach or strong chlorine products: they can mark the boards and harm plants and pets.
Algae is a slip risk. If part of the deck stays wet and green, the fix is usually better drainage and airflow, cutting back overhanging plants, and cleaning more often in that spot.
Grease and food stains
Barbecue fat and food spills are the most common stains. Deal with them quickly:
- Blot up what you can with kitchen roll.
- Scrub with hot water and washing-up liquid, along the grain.
- For older grease marks, use a degreaser that the board maker approves.
On capped boards most grease comes out completely if cleaned within a day or two. On uncapped boards it can soak in, which is one of the main reasons capped boards are worth the extra.
Leaf and tannin stains
Wet leaves left on a deck can leave brown shadows, especially oak and sycamore leaves on light boards. Sweep leaves off every week or so in autumn. Most tannin marks fade in sunlight over a few weeks, and a composite deck cleaner speeds that up.
Rust marks
Rust usually comes from metal furniture feet, barbecues or tools left on the deck. Use a cleaner made for rust on composite, and put pads or a mat under metal furniture.
Can you pressure wash composite decking?
Many board makers allow it, with care:
- Use a fan nozzle, not a pin jet.
- Keep the lance well back from the surface; check the maker’s guidance on distance and pressure.
- Move along the grain, never across it.
- Never hold it in one spot.
Too much pressure, too close, can damage the cap and roughen the surface, which then holds more dirt. If in doubt, use a brush.
Snow and ice
Use a plastic shovel, not a metal one, and push along the boards. Rock salt (sodium chloride) and calcium chloride de-icers are usually fine on composite, but rinse the deck in spring. Avoid sharp tools to chip ice.
What to avoid
- Wire brushes and scouring pads
- Bleach and strong solvents such as acetone
- Oil, stain or varnish: composite does not need it and it will not take evenly
- Rubber-backed mats left down for long periods
- Dragging heavy furniture
A deck that is cleaned in spring and autumn will look far better at ten years old than one that is only cleaned when it looks dirty. If you are still choosing boards, the board comparison on our homepage shows how much upkeep each board needs.