Complete Guide to Pressure Cleaning Composite Decking Boards

Composite decking is a popular choice for Mawson Lakes homes, particularly those near the lakes and wetlands where outdoor entertaining areas get plenty of use. It's often marketed as low maintenance, but that doesn't mean no maintenance. Over time, composite boards collect dirt, pollen, mould, algae and organic stains. Pressure cleaning can bring them back to a fresh look, but only if it's done correctly. Used the wrong way, a pressure washer can damage the surface and even void your warranty.

This guide explains how to clean composite decking safely, what pressure settings to use, which mistakes to avoid, and when it makes sense to call a professional.

Why Composite Decking Needs Regular Cleaning

Composite boards are made from a blend of wood fibres and recycled plastics, or in some cases from fully capped PVC-style materials. They resist rot and termites far better than natural timber, but their surfaces still attract buildup. In the Adelaide climate, with hot dry summers and damp winters, several things commonly affect decks in Mawson Lakes:

Mould and mildew: Shaded areas, or decks near gardens and water features, hold moisture and encourage black and green growth.
Algae and moss: These appear in damp, shaded spots and can make boards slippery.
Tannin and leaf stains: Fallen leaves from nearby trees leave brown marks on the surface.
Dust and grime: Dry summer conditions and wind-blown dust settle into the board texture.
Food, drink and grease marks: Common on decks used for barbecues and entertaining.
Bird droppings and pollen: These can stain if left for long periods.

Regular cleaning not only improves appearance but also helps prevent slippery surfaces and keeps the boards performing as the manufacturer intended.

Can You Pressure Clean Composite Decking?

Yes, in most cases you can, but with care. Composite boards are more delicate than concrete or pavers. Many have a brushed or embossed surface texture, and some have a thin protective capping layer. High pressure can strip or roughen that layer, lift fibres, leave streaks, or etch visible marks into the boards.

Always check the manufacturer's care guidelines first. Some brands recommend only low-pressure washing, while others advise against pressure washers entirely and suggest soft brushing with detergent. Using a method outside those guidelines can affect your warranty.

Recommended Pressure Settings

As a general rule, composite decking should be cleaned with low to medium pressure. Many manufacturers suggest staying under roughly 1,500 PSI (around 100 bar), though this varies by product. Other key settings include:

Nozzle Choice

Use a wide fan tip, such as a 40-degree nozzle. Avoid narrow, zero-degree or turbo nozzles, which concentrate the force and can gouge the surface.

Distance

Keep the nozzle at least 30 centimetres from the boards, and increase the distance if you see any change in the surface texture. Test a small, hidden area first, such as a board edge near the house or under a planter.

Direction

Always spray in the direction of the board grain, moving along the length of each board. Spraying across the grain or at sharp angles can force water into gaps and leave visible lines.

Step-by-Step Process for Cleaning Composite Decking

Clear the deck. Remove furniture, pots, mats and barbecues. Sweep away loose leaves and debris.
Clean between the boards. Use a plastic scraper or putty knife to clear leaf litter and dirt from the gaps. Trapped debris holds moisture and promotes mould growth.
Wet the surrounding plants. Lightly water nearby garden beds and lawn to help protect them from cleaning solution runoff.
Apply a composite-safe cleaner. Use a detergent made for composite decking, or a mild solution recommended by the manufacturer. Avoid harsh chemicals unless the manufacturer approves them.
Let it dwell. Allow the cleaner to sit for the time stated on the label, usually 10 to 15 minutes. Do not let it dry on the surface.
Scrub stubborn areas. Use a soft-bristle deck brush, working along the grain. Avoid stiff wire brushes, which scratch the surface.
Rinse with low pressure. Use a wide fan nozzle and work in even, overlapping passes along the length of the boards.
Allow to dry fully. Check the deck in daylight once it's dry to spot any missed patches or stains.

Choosing the Right Cleaning Products

Not all cleaners are suitable for composite materials. Some can cause fading or discolouration, particularly on darker boards that are already exposed to strong Australian sun. Consider these points:

Mild Detergents and Specialist Cleaners

Composite-specific deck cleaners are formulated to lift grime without damaging the surface. For light dirt, a mix of warm water and a mild household detergent often works well.

Mould and Algae Treatments

For persistent mould, a diluted oxygen-based cleaner (sodium percarbonate) is often gentler than chlorine bleach. Some manufacturers do permit diluted bleach solutions, but check first, and rinse thoroughly to protect surrounding plants and lawn.

Products to Avoid

Avoid strong acids, solvent-based degreasers, and abrasive powders unless the manufacturer specifically allows them. These can dull or discolour the finish.

Common Mistakes to Avoid

Using too much pressure: This is the most common cause of damage. Higher PSI doesn't mean better results on composite.
Using a narrow or rotating nozzle: These can leave permanent marks on the boards.
Holding the wand too close: Close-range spraying can fuzz the surface or strip the cap layer.
Skipping the test patch: Different brands and colours react differently to cleaners and pressure.
Cleaning in direct midday sun: On hot Adelaide days, cleaner can dry too quickly and leave streaks. Work in the morning or late afternoon.
Ignoring the gaps: Debris trapped between boards promotes mould regrowth.

Dealing With Specific Stains

Mould and Mildew

Apply a suitable mould cleaner, let it dwell, scrub gently and rinse. In shaded areas, you may need to repeat the process once or twice a year.

Grease and Oil

Blot fresh spills straight away with absorbent paper. Treat the area with warm soapy water or a composite-safe degreaser and scrub gently. https://pressurecleaningmawsonlakes.com.au/roof-cleaning/ Older stains may need repeated treatment.

Rust Marks

Metal furniture legs and plant pots can leave rust stains. A rust remover that is safe for composite materials can help, but test it first in a hidden spot.

Tannin Stains

Leaf stains typically fade with a deck cleaner and a soft brush. Sweeping leaves regularly helps prevent them from setting in.

How Often Should You Clean Composite Decking?

For most Mawson Lakes homes, a thorough clean once or twice a year is a good baseline. Decks that are heavily shaded, near trees, or close to the water may need cleaning more often. Between full cleans, a few simple habits make a big difference:

Sweep weekly or fortnightly to remove leaves and dust.
Wipe up spills promptly.
Rinse the deck with a hose every few weeks during dry, dusty periods.
Trim back overhanging branches to reduce shade and leaf drop.
Use mats or pads under pots and furniture to avoid trapped moisture and rust marks.

Local Considerations for Mawson Lakes

Mawson Lakes properties often back onto wetlands, reserves or landscaped water features. These settings are beautiful, but they bring more humidity, insects, bird activity and organic debris, all of which can speed up mould and staining on outdoor surfaces. Strong summer UV also affects composite boards, and fading can sometimes be mistaken for dirt. If a section looks dull after cleaning, it may be sun exposure rather than grime.

Also be mindful of runoff. Because many properties are close to stormwater drains and water bodies, avoid letting harsh chemicals wash into the drainage system. Choose biodegradable, composite-safe products and direct wastewater onto lawn or garden beds where appropriate, in line with local council guidance on stormwater protection.

DIY or Hire a Professional?

Cleaning a small composite deck yourself is achievable with the right equipment and a cautious approach. However, there are situations where professional help is worth considering:

When to Consider a Professional

Your deck is large, multi-level or hard to access.
There is heavy mould, algae growth or long-term staining.
You are unsure about your boards' warranty requirements.
You don't own a pressure washer with adjustable settings.
You want a consistent result without the risk of surface damage.

Professional cleaners use pressure equipment that can be adjusted precisely, along with appropriate detergents and techniques suited to different board types. They can also advise on whether your deck would benefit from other care, such as resealing surrounding pavers or treating nearby timber features.

Maintaining Your Deck After Cleaning

Once your deck is clean, a few ongoing steps help keep it looking good for longer. Keep gutters and nearby vegetation under control, ensure the deck has adequate drainage and airflow underneath, and avoid leaving wet items such as towels or pot saucers on the boards. Some owners also use a composite-safe protective treatment, though not every manufacturer recommends this, so check before applying anything.

Final Thoughts

Pressure cleaning composite decking can restore its appearance and extend its life, as long as you use low to medium pressure, a wide fan nozzle, the right cleaning products and a careful technique. Always check your manufacturer's guidelines, test a small area first, and keep up with regular sweeping and rinsing between deeper cleans. If you'd rather leave it to the experts, a professional pressure cleaning service familiar with Mawson Lakes conditions can deliver a safe, effective clean and help your deck look its best all year round.

Mawson Lakes Pressure Cleaning

Unit 7/12 William St, Cavan SA 5094

(08) 7282 0689