The short answer
Brush off loose dirt, wet the boards, scrub with warm water and a mild detergent or decking cleaner, then rinse well. Do it at least twice a year. Most stains come off with the same method if you catch them early; check your board maker's guide before using a pressure washer or stronger cleaners.
Composite decking is sold as low maintenance, and it is. Low maintenance is not no maintenance, though. Dirt, leaves and algae still settle on the boards, and a deck that is never washed will look tired and can get slippery. The good news is that cleaning it takes an hour or two, a couple of times a year.
How often to clean composite decking
Aim for a proper clean at least twice a year: once in spring before you start using the deck, and once in autumn after the leaves have come down. Clean more often if the deck is:
- under or near trees, which drop leaves, sap and pollen
- in shade, where algae grows faster
- by a barbecue or outdoor kitchen, where grease lands on the boards
- used a lot by children or pets
In between, a quick sweep stops leaves from sitting in one place and staining the boards.
The routine clean, step by step
1. Clear and brush
Move furniture and pots off the deck. Sweep away leaves and loose dirt with a stiff brush. Natural bristles are kinder to the board surface than hard plastic or wire.
2. Wet the boards
Hose the deck down and leave it for 10 to 15 minutes. Wetting first loosens dirt and helps the cleaner work.
3. Scrub
Use warm water with a mild detergent, or a cleaner made for composite decking. Scrub along the length of the boards, following the grain pattern, rather than across them.
4. Rinse thoroughly
Rinse with plenty of clean water so no cleaner is left to dry on the surface. Leftover detergent can leave a film that attracts dirt.
Can you pressure wash composite decking?
Often yes, but carefully, and only if your board maker allows it. Some makers forbid pressure washers; others allow them with limits. As an example, Millboard’s own care guide says to:
- keep the pressure at or below 2,000 PSI
- use a wide fan tip of 40 to 60 degrees, not a narrow jet
- hold the nozzle at least 300 mm from the surface
Too much pressure, or a nozzle held too close, can scar the surface or expose fixings. If you’re not sure which boards you have, a brush and bucket is the safe choice.
Removing common stains
Catch stains early. Most come off far more easily in the first day or two.
| Stain | What usually works |
|---|---|
| Grease, oil, food | Warm water, mild detergent and a soft brush, straight away |
| Tree sap | An oil soap left for about 15 minutes, then scrubbed; older patches may need repeating |
| Rust from furniture or tools | A rust and limescale remover approved by the board maker |
| Green algae | The routine clean, more often in shady spots |
| Building dust or cement | A cleaner made for construction residue; test it first |
Always test any cleaner on a small hidden area first, and check the board maker’s list of approved products.
Cleaning after winter
Winter is hardest on any deck. Leaves sit in the gaps, moss grows in shady corners and grit from icy mornings collects on the boards. In early spring:
- clear the gaps between boards with a thin scraper or a putty knife so water drains freely
- check under pots and furniture for marks and damp patches
- give the whole deck the full routine clean above
- look over fixings, fascias and steps for anything loose
A thorough spring clean usually takes an afternoon for a typical garden deck, and sets it up for the summer.
What to avoid
- Harsh solvents and bleach, unless the board maker specifically approves them for a stain.
- Wire brushes and metal scrapers, which scratch the surface.
- Metal snow shovels. Use a plastic shovel or a stiff broom instead.
- Rock salt on ice. It contains grit that can scratch. Millboard recommends white salt instead.
- Sanding. Composite is not timber. Sanding removes the protective cap.
Keeping it clean for longer
- Lift pots on feet so water does not pool underneath.
- Put a mat under the barbecue.
- Trim back plants and trees that drop onto the deck.
- Keep the gaps between boards clear so water drains away.
Cleaning and choosing boards
How easy a deck is to clean starts when the boards are chosen. Capped composite boards have a protective outer shell that resists staining and fading, and they are usually easier to clean than older uncapped boards. If you’re planning new decking, ask the installer whether the boards are capped and what the maker’s care guide says. See our composite decking page for what else to ask for in a quote.
Thinking about composite decking in Sheffield? The quote form takes two minutes, and a local installer can talk you through board options at the visit.