To clean composite decking, remove loose debris, use the cleaner and brush specified for your boards, gently scrub a small area, then rinse thoroughly and let it dry. Warm water and mild soap suit many products from leading brands, but the correct method depends on the brand and range. A pressure washer is optional, and some older boards should not be pressure washed.
Before you buy a cleaner, identify the boards
“Composite” is not a cleaning specification. Capped composite, older uncapped boards and PVC decking can need different products and brushes. Check your invoice, handover pack or a spare board for the manufacturer and range. If the deck came with the house, ask the previous owner or installer before trying a specialist treatment.
Save the care guide for that exact product. Check the permitted cleaner, brush, dilution, contact time and rinsing method. A bottle labelled “deck cleaner” may be intended for timber. A recommendation for one brand is not permission to use it on another.
How to clean composite decking step by step
For routine cleaning, gather a broom, bucket, hose, the specified cleaner and a suitable non-metal brush. Brush requirements vary: some boards need soft bristles, while Millboard specifies a stiff natural-bristle brush. Follow your product’s instructions rather than assuming one brush suits every deck. Choose a time when the surface is cool and there is no frost risk.
- Clear the space. Lift furniture and pots instead of dragging them. Sweep grit, leaves and loose dirt from the surface and steps. Clear accessible debris from board gaps without gouging the edges or disturbing fixings.
- Plan where the wash water will go. Move portable pots and check the cleaner’s instructions for planting, ponds and runoff. Avoid washing dirt towards door thresholds. Keep people and pets out of the work area.
- Prepare one manageable section. Follow the care guide on pre-wetting. Measure the cleaner rather than adding an extra splash. A stronger mixture is not automatically more effective or safer.
- Brush the surface gently. Work into the texture using the specified brush and method. Give a specialist cleaner only its stated contact time; do not borrow the soaking time from a different product.
- Rinse before moving on. Remove loosened dirt and cleaner completely. For a wash-and-rinse product, work in sections small enough to keep the solution from drying on the boards.
- Inspect when dry. Look at the test patch and the whole section in similar light. If a mark remains, identify it before repeating the process or changing products.
Leading brands recommend checking the care instructions for the particular board before cleaning. For example, Dino’s cleaning guide covers mild soap and water, while TimberTech’s care advice stresses testing first and working in small areas. Product-specific instructions take priority over a general routine.
Can you jet wash composite decking?
Sometimes, but there is no safe pressure setting for every composite deck. Check whether your exact boards allow pressure washing before switching the machine on. The permitted pressure, nozzle and working distance all matter.
Trex permits a fan tip and a maximum of 3,100 psi on its Transcend, Enhance and Select ranges, with the nozzle at least 203mm from the surface. Its guidance for early-generation boards differs and advises against pressure washing. Those limits are product-specific ceilings, not a target for an unknown deck. See the relevant tab in the Trex care guide.
If you cannot identify the boards, use a hose and manual cleaning while you obtain guidance. Do not substitute a turbo nozzle or rotary patio attachment for an approved fan tip. If hiring a cleaner, ask them to name the board range, proposed product and pressure method in advance, and agree a dry test patch before the whole deck is treated.
Match the cleaning method to the mark
How do you remove barbecue grease and food stains?
Blot a fresh spill promptly, then use the board maker’s approved grease-cleaning method. Avoid spreading it across several boards. Trex requires food, oil and grease to be removed within seven days to maintain its stain warranty; that is not a reason to leave a spill until day seven. Check your own warranty’s conditions.
If grease remains after an approved wash, adding more products is not necessarily the answer. For an old stain, send the manufacturer a dry photograph and a list of everything already used. Ask for an approved next step; not every absorbed stain can be removed.
Why is the deck green, black-spotted or slippery?
Damp leaves and debris can encourage surface mould and algae. Remove the build-up, clean with the approved method and address places that stay wet. Keep the surface and board gaps clear. Even low-maintenance decking can become slippery when contaminated with algae.
Look for a pattern: does growth return beneath pots, in a shaded corner or beside a leaking gutter? Note where water remains after the rest has drained. Cleaning removes contamination; repeated pooling needs investigation. Do not drill drainage holes or widen gaps as a cleaning shortcut.
Why do white marks come back when the deck dries?
White marks do not always mean the deck needs stronger cleaning. Check for residual cleaner or dirty rinse water first. Hard-water deposits are another possibility; surface damage can also look pale. A photograph alone cannot reliably distinguish them.
Rinse a small test area with clean water, let it dry and compare. Trex has a separate hard-water section in its care guide, but do not transfer its stain treatments to unidentified boards. If rinsing does not help, or the texture has changed, stop and ask the manufacturer before adding an acid, abrasive or restorer.
What about rust, leaf stains and scratches?
Record what sat above the mark: a metal chair foot, a pile of wet leaves or a dragged planter provides useful context. Remove the source and ask for the board maker’s treatment for that stain. Avoid using patio acid or a timber brightener just because it removes a similar-looking mark elsewhere. A scratch or burn is physical damage; scrubbing harder will not clean it away.
Can you use washing-up liquid, bleach or vinegar?
- Washing-up liquid: Mild detergent and warm water are accepted by several leading brands, but check the exact product first and rinse thoroughly. Avoid assuming that every household detergent suits every board.
- Bleach: Do not use it on unidentified decking. Some manufacturers prohibit it; use it only if your exact board’s care guide explicitly allows the product and method.
- Vinegar or bicarbonate of soda: neither is a universal composite cleaner. Use a household treatment only where the manufacturer explicitly approves it for your product and problem.
- Specialist composite cleaner: check compatibility, dilution and label directions. Its application and contact time may differ from a quick soap wash. Choose a product approved for your boards and the stain you are treating.
Use one cleaning product at a time and never mix bleach with vinegar, acids or other cleaners. Follow the label’s protective-equipment and access instructions. “Natural”, “eco” or “bleach-free” is not permission to ignore dilution or runoff precautions.
Will the cleaner harm plants or pets?
Check the actual product label, including what it says about nearby planting, aquatic life and when people and pets can use the area again. Suitability for composite decking does not establish safety for plants or animals.
Trace the runoff route before you start, especially on a balcony or raised deck above planting or another outdoor space. If the instructions do not cover your situation, ask the product supplier. Do not assume a cleaner suitable for the boards is harmless to everything beneath them.
How do you clean Millboard decking?
Millboard is made from mineral polymer resin, so use its own care instructions rather than treating it as a wood-plastic composite. Its official aftercare guide (PDF) recommends warm water with household detergent, scrubbing into the grain and rinsing thoroughly. Pre-wet the area 10–15 minutes before applying a cleaning solution and test first.
For pressure washing, Millboard specifies no more than 2,000 psi, a 40–60° fan tip and a working distance of around 300mm. It warns that intense or prolonged contact can damage the surface and that washing may make screw holes more visible. These limits apply to Millboard, not every decking brand.
For persistent grease, rust or building-dust stains, consult the guide’s stain-specific instructions rather than increasing detergent strength. It lists different treatments for different contamination; follow the relevant product label and test in a hidden area.
How often should you clean it?
Millboard recommends cleaning twice a year or as needed. Spring and autumn are useful reminders, with spills dealt with immediately and leaves cleared as needed. A shaded garden with overhanging trees may need attention between seasonal washes. Inspect the deck after heavy leaf fall and before putting furniture back out for summer.
- Keep a note of the board range, approved cleaner and care-guide link with your household records.
- Check beneath movable pots and furniture when sweeping, rather than only cleaning the open walking area.
- Use only mats and protective accessories compatible with the decking; check before leaving a barbecue mat in place.
- Photograph any persistent mark when dry, noting when it appeared and what has already been tried.
There is no need to turn a cosmetic mark into a replacement project. But loose boards, movement or an unsafe step need assessment separately from cleaning. Our composite decking lifespan guide explains the distinction between the boards and the structure supporting them.
Planning a new composite deck?
Ask for the exact board name and care guide with your installation handover. London Decking Specialists installs composite decking in London and undertakes full replacements. This guide is for looking after your deck; we do not offer standalone cleaning or small repairs.