Quick answer: Clear the deck, sweep away debris, and rinse with a hose. Mix warm water with a few drops of mild washing-up liquid, scrub along the length of the boards with a soft-bristled brush, working into the gaps, then rinse thoroughly. Never use bleach, since it can discolour and damage composite material, and avoid a jet washer unless used on a low-pressure setting with extreme caution.
Composite decking is prized for needing far less maintenance than timber, but low maintenance does not mean no maintenance. Regular cleaning keeps it looking its best and prevents the kind of build-up that can eventually affect its surface and drainage.
Why Composite Decking Still Needs Cleaning
Composite decking is manufactured from a mix of wood fibres and plastics, usually HDPE, which makes it more resistant to staining, rotting, and warping than solid timber. It does not need regular treating, staining, or painting the way timber decking does. That said, dirt, algae, and organic debris still settle on the surface and in the gaps between boards, and left unaddressed for long periods, this build-up can affect both appearance and drainage.
What You Will Need
- A broom or leaf blower
- A garden hose
- Mild washing-up liquid, or a dedicated composite decking cleaner
- A soft-bristled brush (never a stiff wire brush)
- A putty knife or scraper, for gaps between boards
- Rubber gloves
Step 1: Clear and Sweep
- Remove all furniture, plant pots, and other items from the deck so the whole surface is accessible.
- Sweep away leaves, twigs, and loose debris with a broom, or use a leaf blower for a larger area.
- Clear debris trapped between the boards using a putty knife or scraper, taking care not to scratch the surface as you work. Clearing these gaps also matters for drainage, since blocked gaps can allow water to pool rather than drain away properly.
Step 2: Rinse
Hose down the whole deck with clean water before applying any cleaning solution. This loosens surface dirt and makes the actual cleaning step considerably easier, since you are not trying to scrub dry, compacted grime.
Step 3: Apply Cleaning Solution
- Mix warm water with a few drops of mild washing-up liquid, or prepare a dedicated composite decking cleaner following the manufacturer’s instructions.
- Apply the solution to a manageable section of decking at a time, working in the direction of the boards rather than across them.
- Leave the solution to sit for a few minutes on stubborn areas, adding more if it starts to dry out before you have finished scrubbing.
Step 4: Scrub
- Scrub the deck with a soft-bristled brush, working along the length of each board rather than side to side.
- Use a smaller brush or sponge to work into gaps, corners, and any embossed pattern on the board surface, since dirt tends to concentrate in these areas.
- Pay extra attention to any heavily soiled patches, repeating the process if needed rather than scrubbing harder with a stiffer brush.
Always use a soft brush rather than a medium or hard-bristled one, since stiffer bristles can leave permanent scratches and marks on the composite surface.
Step 5: Rinse and Dry
- Rinse the entire deck thoroughly with a hose, making sure all traces of soap or cleaning solution are removed, since leftover residue can make boards slippery once dry.
- Allow the deck to dry completely before returning furniture, pots, or mats to the surface.
Removing Specific Stains
Bird Droppings
Wear gloves before handling any bird mess. Remove the bulk of it with a broom, hose, or gentle pressure wash, then clean any remaining residue with mild detergent, a soft brush, and a bit of extra effort. This rarely needs anything stronger than your standard cleaning solution.
Mould and Algae
A dedicated oxygenated composite decking cleaner is effective on mould and algae without the discolouration risk that bleach carries. Apply as directed, leave to work for the stated time, and rinse thoroughly.
What to Avoid
- Bleach: even diluted household bleach can cause composite boards to discolour and chip more quickly over time. Avoid it entirely, and never mix it with a specialist decking cleaner in an attempt to boost its effect.
- Stiff or wire brushes: these scratch the surface, and unlike dirt, scratches cannot be cleaned away afterwards.
- High-pressure jet washing: a pressure washer can be used with extreme caution on capped composite decking at a low setting, but it is not recommended at all on uncapped boards, since the material is often softer than solid timber and more prone to surface damage. If you do use one, always use a fan tip nozzle rather than a narrow, concentrated jet, and test on a hidden area first.
- DIY chemical mixes: stick to mild soap and water or a genuine composite decking cleaner rather than experimenting with combined household chemicals, which can produce unpredictable results on composite material.
Sealing After Cleaning
Once your deck is clean and completely dry, applying a composite deck sealer designed for the purpose can help protect the surface from staining and general wear going forward, extending the time between deep cleans.
How Often Should You Clean Composite Decking?
A full clean twice a year, typically in spring and autumn, is generally sufficient for most composite decks. Between these deeper cleans, sweeping away debris regularly, mopping up spills promptly, and using furniture pads under table and chair legs will keep the deck looking good with minimal extra effort.
Related Guides
Frequently Asked Questions
Can I use a pressure washer on composite decking?
Only on capped composite decking, and only on a low-pressure setting with a fan tip nozzle, used with caution. It is not recommended at all on uncapped boards, which are more prone to surface damage.
Why should I avoid bleach on composite decking?
Bleach, even diluted, can cause composite boards to discolour and chip more quickly than mild soap and water or a dedicated composite cleaner.
How often should composite decking be cleaned?
A full clean twice a year, typically spring and autumn, is generally enough, alongside regular sweeping and prompt spill clean-up in between.
Why is it important to clean the gaps between decking boards?
Debris trapped in the gaps can block proper drainage, causing water to pool on the surface rather than draining away as intended, which increases the risk of surface staining and slippery patches.
Final Thoughts
Composite decking rewards a simple twice-yearly clean with warm soapy water and a soft brush, without needing the regular treating and staining that timber decking demands. Stick to mild cleaning solutions, avoid bleach and stiff brushes, and keep the gaps between boards clear to protect both the look and the drainage of your deck for years to come.