Grime, mould, and algae build up so gradually on driveways, decks, and exterior walls that most people don't notice how far it's gone until they see a "before and after" photo — or a freshly cleaned neighbour's place next door. Here's a practical guide to how often different surfaces actually need it, and why the wrong approach can cause more problems than it solves.
How often different surfaces need it
- Concrete driveways and paths — generally every 12–18 months, sooner if there's heavy tree cover or the surface stays damp and shaded for long periods
- Timber decks — typically once a year, ideally before re-oiling or re-staining, since cleaning first gives any coating something proper to bond to
- Exterior walls (render, brick, cladding) — every 2–3 years for most homes, more often on south-facing or heavily shaded walls prone to mould and algae
- Pool surrounds and outdoor entertaining areas — every 6–12 months, since these areas tend to stay damp and see the heaviest foot traffic
These are general guides rather than fixed rules — a shaded, damp block in Sydney's wetter suburbs will need attention more often than an exposed, sun-drenched one.
Signs it's overdue
A few reliable indicators, regardless of the surface: a greenish or black tinge appearing in shaded corners, a driveway or path that feels slightly slippery even when dry, and painted or rendered surfaces that look dull rather than genuinely faded. Any of these usually means the surface has been due for a clean for a while, not that it's just starting.
Why DIY pressure washing can go wrong
A consumer-grade pressure washer at the wrong setting, angle, or distance can cause real damage rather than just cleaning:
- Stripping mortar joints — too much pressure on brick or paving can wash out the mortar between joints over time
- Forcing water under tiles or decking boards — rather than cleaning the surface, this can push moisture into places it then can't easily escape from
- Damaging timber fibres — too high a pressure or too close a distance can "fuzz" or gouge softwood decking, leaving a rougher surface than before
- Uneven cleaning patterns — inconsistent passes can leave visible streaking on concrete and render that's more obvious than the original grime
None of this means pressure washing itself is risky — it's almost always about pressure, nozzle choice, and technique being matched to the specific surface.
What heavy-duty equipment actually changes
Professional-grade pressure washing equipment isn't just "stronger" — it allows for far more control, with adjustable pressure and nozzle combinations matched to the surface, rather than one fixed setting trying to do everything from timber to concrete. That control is usually the difference between a surface coming up clean and even, versus patchy or, in the worst cases, damaged.
Frequently asked questions
Will pressure washing remove oil or rust stains from concrete?
Fresh, light staining often lifts well. Older or deeply set oil and rust stains usually need a degreasing or chemical treatment alongside pressure washing to fully clear, rather than pressure alone.
Is pressure washing safe for older or weathered concrete?
Generally yes, at the right pressure setting, but older concrete that's already cracking or spalling should be assessed first, since very high pressure can worsen existing surface damage.
How long do the results typically last?
This depends heavily on shade, moisture, and foot traffic, but most surfaces stay noticeably cleaner for 6–18 months before regrowth of mould or algae becomes visible again.