Soft washing uses low-pressure water and cleaners to safely remove mould, mildew, and algae from timber decks, cladding, and composite surfaces. It kills growth at the root without damaging wood fibres or composite finishes, unlike high-pressure methods that cause splintering, gouging, or streaking. This approach suits humid areas like Australia, where coastal mould thrives.
In this guide, you will learn what soft washing is and why it is safer than high-pressure for timber and composite surfaces. We will cover how pressure can damage wood and still mark composite, why soft washing removes mould and mildew better, the basic safe process, what to avoid, key safety and runoff notes, how to keep surfaces cleaner longer, and when to hire a pro.
What soft washing is
Soft washing cleans surfaces with low-pressure water and cleaning solutions. It targets dirt, mould, and mildew on delicate materials like timber and composite.
The method relies on chemistry to break down contaminants. Water pressure stays below 100 psi, like a garden hose. This protects the surface from harm.
Read about what soft washing is if you want to gain a deeper understanding.
Why does high pressure damage timber and cladding
High-pressure washing harms timber by forcing water deep into the wood. It raises grain on timber decks and cladding. Splintering happens when pressure blasts soft wood fibres. Gouging creates deep marks if the nozzle gets too close. Uneven stripes appear from inconsistent passes. Water pushes into joints, causing swelling or rot over time. Coatings strip away, leaving timber exposed to the weather. In my 13 years, the most common deck damage I see is splintered boards from DIY high-pressure jobs.
How to spot high-pressure damage (quick checklist)
You can spot high-pressure damage by looking for changes you did not have before.
- The timber feels fuzzy or rough (raised grain)
- You see bright, fresh lines next to darker lines (uneven stripes)
- The surface has small splinters or lifted fibres
- Stain or paint looks patchy, thin, or peeling
- Water sits in joints longer, or boards look swollen at the edges
Why high pressure can still damage the composite
High-pressure washing scratches composite surfaces even if they feel tough. Scuffing dulls the finish on WPC boards. Streaking leaves permanent lines from uneven force. Surface finish wears down, exposing the inner material. Capstock, the protective layer, erodes under strong jets.
Grime traps in textured areas, leading to stubborn stains. In my experience, composite decks show hazy spots after high-pressure misuse. Always follow the manufacturer’s care guide to avoid voids in warranties.
Warranty check reminder
Review your composite brand’s care guide before cleaning. Most warn against pressures over 1500-3100 psi. Test a small area first. Damage from high pressure often nulls coverage.
Why soft washing works better on mould, mildew, and algae
Soft washing kills mould, mildew, and algae at the root with chemistry. Cleaners penetrate surfaces to destroy spores. Dwell time lets solutions work without scrubbing hard. Low-pressure rinse removes residue gently. High pressure only blasts surface film, leaving roots to regrow. This method suits shaded homes in Sydney, where humidity fosters growth. In Australian coastal areas, soft washing handles salty mould buildup well.
Read dwell time for the simple signs that tell you when a surface is ready to rinse.
Rinsing matters because leftover residue can dry into haze or sticky patches. Read rinse and neutralise to avoid streaks, plant stress, and dull finishes.
Timber vs composite: choose the right approach (quick decision guide)
Timber and composite fail in different ways, so the best approach changes.
Use this quick guide to avoid the most common mistakes.
| Surface type | Biggest risk | Best approach | What to avoid |
| Timber deck boards | Raised grain, gouges, water intrusion | Soft wash, light agitation with a soft brush, thorough rinse, let it dry | Narrow jets, close-range blasting, harsh solvents |
| Timber cladding | Water forced into joints, coating lift | Soft wash in sections, controlled runoff, gentle rinse | Spraying upward into laps, soaking joints |
| Composite decking (WPC) | Scuffs, streaks, and cap layer wear | Follow the manufacturer’s care guide, soft wash, soft brush, and even rinse | Abrasive pads, harsh degreasers, high-pressure close-up |
The soft washing process (safe overview, not a recipe)
Soft washing works best when you work in small sections and keep the surface wet.
This helps the cleaner work evenly and makes rinsing simple.
Step 1: Check what you are cleaning (timber vs composite)
You get better results when you match the method to the material.
Timber can raise grain and soak water at joints. Composite can scuff and streak if you scrub too hard or use the wrong tool.
- If it is timber: plan to brush with the grain and avoid flooding gaps and end grain.
- If it is composite (WPC): plan to clean the texture and grooves gently and follow the board brand’s instructions.
Step 2: Do a quick safety and setup check
You prevent most problems when you set up before you spray.
Move slowly, and think about plants, nearby cars, and where rinse water will flow.
- Put on basic PPE (gloves and eye protection).
- Pick a calm time with low wind.
- Check the deck slope and find where water drains.
Step 3: Clear the area
You clean more evenly when nothing blocks your path.
Remove furniture, mats, pots, toys, and BBQ covers so you do not miss edges and corners.
Step 4: Dry remove loose grit first
You avoid scratches when you remove dry dirt before washing.
Sweep or blow off sand and leaves, because grit acts like sandpaper when it gets wet.
Step 5: Protect plants and nearby surfaces
You reduce plant stress when you pre-wet and shield sensitive areas.
Fresh water helps dilute splash and runoff, especially near garden beds.
- Pre-wet plants and grass with fresh water.
- Rinse plants again after you finish.
Read about: protective plants and landscaping during soft washing, if you want a simple checklist.
Step 6: Do a small test patch first
A test patch tells you how the surface reacts before you do the full area.
Clean one small spot, rinse it well, then let it dry fully before you decide.
Pick a hidden area like a corner or behind a pot.
If timber turns fuzzy or composite looks dull, change your approach before you continue.
Step 7: Apply a suitable cleaner for the material
A suitable cleaner does the cleaning, so you do not need to force.
Follow the product label and the manufacturer’s care guide for timber or composite.
- Apply evenly.
- Work in sections, so it does not dry on the surface.
- Keep it off items you do not want to clean, like bare metals or fabric cushions.
Step 8: Let it dwell, but do not let it dry
Dwell time is the wait that lets the cleaner loosen grime and organic growth.
If it dries, it can leave residue and streaks.
- Keep the area shaded if you can.
- Re-wet lightly if the surface starts to dry.
- Do not rush this step.
Step 9: Use gentle agitation only where needed
Gentle brushing helps in grooves, corners, and heavy growth.
Use a soft-bristle brush and light pressure.
- Timber: brush with the grain and avoid digging into soft boards.
- Composite: brush along the board direction and clean the texture, not with hard scrubbing.
Step 10: Rinse thoroughly with low force
A full rinse removes loosened dirt and prevents haze.
Rinse until the water runs clear, and you see no foam, film, or slick feel.
Rinse in the same small sections you cleaned.
Do not blast close range, because that defeats the point of soft washing.
Step 11: Check results after full dry-down
Dry-down is the real result check because wet surfaces lie.
Many decks look patchy while wet, then even out when dry.
If you still see stains after drying, you may have tannin, rust, grease, or coating failure.
Read soft wash staining troubleshooting if marks stay after proper rinsing and drying.
Step 12: Control runoff and clean up
Runoff planning protects drains, gardens, and nearby property.
This matters a lot in Sydney and across Australia, where storm drains often flow to waterways.
- Rinse away from doorways and garage edges when possible.
- Keep wash water out of storm drains.
Read about: Overspray and runoff control to plan where water will go, especially on sloped decks and cladding.
Quick “stop” signs (when to pause and reassess)
You should stop when you see early damage signs.
Pause if timber starts to fuzz badly, if the composite dulls, or if you cannot control runoff.
If access is high, the surface is failing, or mould keeps returning, it is safer to hire a professional pressure cleaner.
What not to use on timber and composite
Avoid common mistakes that ruin surfaces. Skip abrasive brushes on both materials; they scratch composite and raise timber grain. Harsh solvents dissolve coatings on timber and dull composite. Too much pressure gouges wood and etches WPC.
Leaving soap residue attracts dirt faster. Rushing the rinse traps chemicals, causing streaks. In my hands-on work, rushed jobs lead to the regrowth of mould. Bust these soft washing myths by sticking to gentle methods.
Safety and environmental notes
Safety starts with proper PPE and awareness of risks. Wear gloves, eye protection, and non-slip boots. Follow chemical labels and SDS for handling. Protect eyes and skin from splashes. Never spray in the wind to avoid drift. Keep runoff out of storm drains; it pollutes waterways. In Australia, follow the NSW EPA stormwater pollution guidelines for clean practices.
Read the Safe Work Australia guide on high-pressure water jetting risks and the WorkSafe safety alert on high-pressure water jetting if you use any pressure equipment at all.
How to keep decks and cladding cleaner for longer
Prevention reduces cleaning needs through simple habits. Trim plants to improve airflow around decks. Regular light rinses wash away pollen. Faster drying prevents mould in humid weather, common in Australia. Re-oil timber after full drying for protection. Shade management helps in Sydney’s shaded homes, where moisture lingers.
When to hire a professional
Hire a professional for complex or risky jobs. Triggers include multi-storey cladding access. Heavy black mould signals deep issues. Unknown coatings need expert testing. Failing timber risks structural harm. Drainage limits or poor safety controls add danger. In my 13 years, pros handle these safely with tools and knowledge.
How much does it cost to pressure wash a 12×12 deck? Costs vary by deck condition, location, and access. Factors like mould severity or surface type influence quotes. Get estimates from licensed cleaners without fixed prices.
If you want to understand what pros do differently, start with pressure cleaning methods and what pressure cleaning is.
FAQs: Frequently Asked Questions
Can you soft wash a composite deck?
Yes, soft washing cleans composite decks safely. It uses low pressure and mild cleaners to remove dirt without damage. Follow the manufacturer’s care guide for best results.
What can you wash composite decking with?
Use mild soap and water or brand-approved cleaners on composite decking. Avoid harsh chemicals. Always follow the product label and manufacturer’s care guide.
Should you use a pressure washer on composite decking?
Avoid high-pressure washers on composite decking if possible. They can cause scuffing or capstock wear. If needed, keep under 1500-3100 psi per brand guidelines.
Can you use Karcher patio cleaner on composite decking?
Karcher patio cleaners work on composite if set to low pressure. Check the brand’s care guide first. Test a small area to ensure no damage.
What should you not use on composite decking?
Do not use abrasive brushes, harsh solvents, or high pressure over the limits of the composite. These cause scratches and wear. Skip bleach unless approved.
What’s the difference between soft washing and pressure washing?
Soft washing uses low pressure and cleaners to kill contaminants—pressure washing blasts with high force, risking damage. Soft washing suits delicate surfaces better.
What ruins composite decking?
High-pressure, abrasive tools, and harsh chemicals ruin composite decking. They cause streaking and capstock erosion. Neglect lets mould trap in textures.
What is the 30cm rule for decking?
The 30cm rule means keeping nozzles at least 30cm from surfaces during cleaning. It prevents gouging on timber or composite. Always follow safety.
How to make composite decking look new again?
Soft wash with approved cleaners to remove buildup. Rinse thoroughly and let dry. Regular maintenance keeps it fresh without damage.
Can I use Simple Green to clean my composite deck?
Simple Green works on composite if diluted per label. It’s mild and effective for general dirt. Check your brand’s guide for compatibility.
