How to Clean Your Composite Decking — The Complete UK Guide

One of the most popular selling points of composite decking is that it requires virtually no maintenance compared to timber. That is true — but "low maintenance" does not mean "no maintenance". Like any outdoor surface, composite decking boards collect dirt, pollen, fallen leaves, algae, and general grime over time. Without occasional cleaning, even the best composite boards will start to look dull, green-tinged, and tired.

The good news: cleaning composite decking properly takes less than an hour for a typical garden deck and requires nothing more specialised than a brush, warm water, and mild detergent. This guide from Paving and Slabs Ltd covers everything from routine maintenance washes to dealing with stubborn stains, algae, mould, and the question everyone asks — can you jet wash composite decking without causing damage?

How Often Should You Clean Composite Decking?

For most UK gardens, a thorough clean twice a year — once in spring and once in autumn — keeps composite decking in excellent condition. The spring clean removes the buildup of winter grime, moss, and algae spores. The autumn clean clears leaf debris and organic material before winter sets in, preventing it from decomposing on the board surface and causing staining.

In addition to these seasonal cleans, a quick sweep every week or two to clear leaves and debris from the board surface and gaps is good practice year-round. Organic material left sitting on the surface holds moisture, which accelerates algae growth — particularly in shaded areas or under overhanging trees.

What You Will Need to Clean Composite Decking

• A stiff-bristle brush or deck scrubbing brush (not wire — wire can scratch composite surfaces)
• A bucket of warm water
• Mild washing-up liquid or a composite decking cleaner
• A garden hose or watering can for rinsing
• A plastic or wooden tool for clearing debris from board gaps (not metal)
• Optional: a pressure washer on a low setting (see guidance below)

Avoid bleach-based cleaning products, solvent cleaners, abrasive pads, or wire brushes. These can damage the composite surface coating, strip colour, and void the product warranty on many composite board ranges.

Step-by-Step: Routine Composite Decking Clean

1. Clear the deck surface. Move all furniture, plant pots, and accessories off the deck. Sweep the full surface with a stiff brush to remove loose debris, leaves, and dirt.
2. Clear the gaps between boards. Use a plastic gap tool, old credit card, or wooden spatula to remove any compacted debris from between the boards. Blocked gaps prevent drainage, hold moisture, and promote algae.
3. Mix your cleaning solution. Add a few squirts of mild washing-up liquid to a bucket of warm water. For heavier soiling or visible algae, a dedicated composite decking cleaner gives better results.
4. Scrub the surface. Working in sections, apply the cleaning solution and scrub in the direction of the board grain with a stiff brush. Always scrub along the grain — not across it — to avoid streaking.
5. Rinse thoroughly. Rinse each section with clean water from a hose before the soap solution dries. Work your way across the deck from the house end outward so you are not walking back across cleaned sections.
6. Allow to dry. Leave the deck to air dry fully before replacing furniture. Check that water is draining freely through the board gaps after cleaning.

How to Remove Algae and Green Moss from Composite Decking

Green algae and moss growth is the most common issue homeowners face with composite decking, particularly in shaded areas or gardens with overhanging trees. Composite boards are far less prone to algae than timber, but in persistently damp or shaded conditions, some surface growth is normal.

To remove algae effectively:

1. Scrub the affected area with a stiff brush and warm soapy water first to loosen the surface growth
2. Apply a dedicated composite decking cleaner or an outdoor algae remover that is safe for use on composite surfaces (always check compatibility — some algae products contain bleach which can damage composites)
3. Leave the product to dwell for the manufacturer's recommended time
4. Scrub again with the grain of the board, then rinse thoroughly with clean water

To prevent algae returning, improve airflow beneath and around the deck where possible, and ensure debris is cleared from the surface regularly so it does not hold moisture. In very shaded positions, an annual application of a composite-safe algae inhibitor can help.

How to Remove Stains from Composite Decking

Different stains require slightly different approaches:

Food and drink stains: Act quickly — fresh stains are far easier to remove than dried ones. Warm soapy water and a scrub brush removes most food and drink spills effectively if tackled promptly.

Oil, grease, and BBQ residue: Apply a degreasing washing-up liquid directly to the stain, work it in with a brush, leave for 5 minutes, then scrub and rinse. Repeat if necessary. For stubborn grease, a dedicated composite deck cleaner formulated for oil stains gives better results.

Rust stains: Rust marks (typically from metal furniture or fixings) require an oxalic acid-based rust remover that is safe for composite surfaces. Apply, leave to dwell, scrub gently, and rinse thoroughly. Always test on a hidden area first.

Tannin stains from leaves: These appear as brown patches where wet leaves have sat on the board surface. Regular cleaning and prompt leaf removal prevents them. Existing tannin stains can usually be removed with a composite deck cleaner — scrub firmly with the grain and rinse well.

Paint or sealant spills: Act immediately before they dry. Wipe with a damp cloth while wet. Once dry, composite-safe paint remover may be needed — always test on an inconspicuous area first.

Can You Jet Wash Composite Decking?

Yes — but with important caveats. A pressure washer can be used on composite decking provided you follow these rules:

• Use a fan-pattern nozzle — never a point or lance nozzle. A concentrated jet will damage the composite surface even on a low pressure setting.
• Keep the pressure below 100 bar — most domestic pressure washers are fine; industrial pressure washers can damage composite surfaces even on low settings.
• Maintain a distance of at least 30cm from the board surface at all times.
• Always work along the grain of the board — not across it.
• Use a sweeping motion — do not hold the jet in one place.

When done correctly, a pressure washer is extremely effective for annual deep-cleans of composite decking, removing algae, dirt, and embedded organic debris quickly. When done incorrectly — too close, too much pressure, or across the grain — it can raise the composite surface fibres permanently.

Seasonal Composite Decking Maintenance Schedule

Spring (March–April): Full clean with brush and composite cleaner. Clear all gaps. Check and tighten any exposed fixings. Inspect the sub-frame beneath for any signs of damage over winter.

Summer (ongoing): Sweep regularly. Wipe up BBQ spills, food, and drink marks promptly. Clear debris after windy weather.

Autumn (October–November): Clear fallen leaves before they decompose on the surface. Full clean before winter. Clear board gaps of all organic debris.

Winter (ongoing): Sweep snow and ice off carefully — avoid metal shovels or scrapers. Composite decking has good frost resistance but removing standing water and ice buildup reduces risk of algae and reduces slip hazard.

Cleaning Composite Decking vs Cleaning Paving Slabs

Composite decking is considerably easier and less time-consuming to clean than most natural stone paving surfaces. Indian sandstone paving, for example, requires periodic sealing on top of cleaning to maintain stain resistance. Porcelain paving slabs share composite decking's low-maintenance advantage — they are also non-porous and require no sealing. For cleaning guidance on paving surfaces, see: How to Clean and Maintain Paving Slabs — Long-Lasting Patio Tips.

If your deck area also has a paved patio at ground level, these cleaning tips apply differently to the two surfaces — always use the correct approach for each material type.

Shop Composite Decking at Paving and Slabs Ltd

Our composite decking range is designed for the UK climate — engineered for easy maintenance, UV-stable, and available in a range of contemporary colours and finishes. Explore:

• Composite Decking Boards — full range with nationwide UK delivery
• Composite Fencing — matching low-maintenance fencing panels
• Porcelain Paving Slabs — for ground-level areas alongside your deck
• Patio Slabs — full patio range for all budgets

For more installation and maintenance guidance, read our Composite Decking vs Patio Slabs guide and our Break-Even Patio Options guide.

---

Frequently Asked Questions — Cleaning Composite Decking

Can I use bleach to clean composite decking?

No. Bleach-based products can strip the colour and damage the surface coating on composite boards. Always use a composite-safe cleaner or mild washing-up liquid instead.

How do I get rid of green algae on composite decking?

Scrub with warm soapy water and a stiff brush, then apply a composite-safe algae remover. Rinse thoroughly. Regular sweeping and keeping debris clear from the surface and gaps significantly reduces algae growth.

Can I use a wire brush on composite decking?

No. Wire brushes scratch and damage the composite surface permanently. Always use a stiff-bristle nylon or natural fibre brush.

How do I remove rust stains from composite decking?

Use an oxalic acid-based rust remover that is compatible with composite surfaces. Apply, leave to dwell for the recommended time, scrub gently with the grain, and rinse thoroughly. Always test on a hidden area first before treating the full stain.