How to Clean Composite Decking — The Right Way

One of the biggest selling points of composite decking is low maintenance — and that's genuinely true. But "low maintenance" doesn't mean "no maintenance," and a quick clean once or twice a year keeps composite decking looking its best and prevents the small problems (leaf debris, pollen, surface mould) from becoming bigger ones.

Here's exactly how to clean composite decking properly and safely.

What You'll Need

• Stiff bristle brush or deck scrubbing brush (not wire/metal bristles)
• Garden hose with a jet nozzle, or a pressure washer set to low pressure
• Bucket
• Composite decking cleaner (or mild soap solution)
• Soft cloth for stain treatment

Routine Cleaning (Every 3–6 Months)

Routine cleaning is straightforward and takes 30–60 minutes for a standard domestic deck:

1. Clear the deck — move furniture, pots, and anything sitting on the surface. Debris trapped under furniture accelerates mould growth.
2. Sweep thoroughly — clear all leaf litter, soil, and organic debris. Pay attention to the gaps between boards where debris accumulates.
3. Wet the surface — rinse the deck with a garden hose to loosen surface dirt.
4. Apply cleaner — use a composite-specific deck cleaner or a diluted solution of washing-up liquid in warm water. Apply with a brush and work in the direction of the board grain (along the length, not across).
5. Scrub — work the cleaner into the surface with a stiff bristle brush. Give extra attention to shaded areas and board gaps where mould can establish.
6. Rinse thoroughly — rinse with clean water, ensuring all cleaner residue is removed. Leftover soap residue can make the deck slippery.

Pressure Washing Composite Decking

Pressure washing is safe for composite decking if done correctly:

• Use a fan nozzle rather than a concentrated jet
• Keep pressure at 80–100 bar maximum — high pressure can damage the surface capping
• Work along the boards, not across them
• Keep the nozzle moving — don't dwell on one spot

Never use a rotary patio cleaner attachment on composite — the high concentration of pressure in a small area can strip the surface finish.

Removing Mould and Algae

Mould and algae growth on composite decking is most common in shaded, north-facing, or damp areas. It typically shows as a grey-green discolouration or black spot staining.

For light growth, the routine cleaning process above will shift most of it. For persistent or established mould:

1. Apply a composite-safe mould and algae remover (avoid bleach — it can discolour some composite products)
2. Allow to dwell for the time specified on the product label
3. Scrub with a stiff brush
4. Rinse thoroughly

Treat with a composite-safe algae inhibitor after cleaning to slow regrowth.

Treating Specific Stains

Oil and grease: Apply a composite degreaser immediately. Work it in with a brush, allow to dwell, then rinse. Don't leave oil sitting on composite — while the surface is resistant, prolonged exposure can leave staining.

Red wine, food, and drinks: Rinse immediately with water. If a mark remains, use a composite cleaner and scrub gently. Most stains on quality capped composite clean off easily if dealt with promptly.

Bird droppings: Remove promptly and rinse clean. Acidic droppings left on composite in hot sun can mark the surface.

Rust marks (from metal furniture legs): Use a composite-safe rust remover. Fit rubber or plastic feet to all metal garden furniture to prevent recurrence.

Leaf tannin staining: Common under deciduous trees in autumn. Regular sweeping during leaf-fall season prevents accumulation. Established tannin stains respond to composite cleaner with some scrubbing.

What NOT to Use on Composite Decking

• Bleach or chlorine-based cleaners — can discolour and degrade the surface capping
• Acetone or solvent-based cleaners — damage the composite material
• Wire brushes or metal scrapers — scratch and damage the surface finish
• Very high-pressure washing (150bar+) — strips the surface capping
• Rotary pressure washer attachments — concentrated pressure damages the board surface

Long-Term Care

Keep the gaps between boards clear of compacted debris by running a narrow brush or blower through them annually. Debris trapped in the gaps is the primary source of mould growth and can also cause moisture retention that shortens board life.

For more comprehensive guidance on composite decking upkeep, see our composite decking maintenance tips guide, and browse our full composite decking range: grey, black, and teak colours.