Walk around any coastal suburb on the East Coast of Australia and you’ll spot it – black streaks on rendered walls, green smudges across rooftops, algae creeping along the edge of shade sails. This isn’t just a sign of age or neglect. Its active biological growth: mould, algae, and lichens thriving on the exterior surfaces of buildings and structures.
And even though it’s in plain sight seen by customers, residents, and the public — it often ends up in the ‘too hard to clean’ basket.
Common Types of Exterior Mould and Algae on Buildings
Australia’s East Coast climate which is humid, warm, and often shaded by trees or built structures creates the perfect breeding ground for a range of fast-growing biological contaminants. Here’s what’s most commonly found on external surfaces and how quickly they take hold:
Cladosporium
- Where it grows: Rendered walls, painted surfaces, fabric shade sails.
- What it looks like: Dark green or black speckled spots.
- How fast it grows: Appears within 1–2 weeks of moisture exposure.
- Risks: Known to trigger asthma and allergic reactions, especially if spores enter indoor areas through windows or vents.
Aspergillus
- Where it grows: Cracks in concrete, paint, and shaded external walls.
- What it looks like: Grey or black powdery mould.
- How fast it grows: Can spread in just 3–5 days under warm, damp conditions.
- Risks: Can cause serious respiratory problems, particularly in children and people with weakened immune systems.
Green Algae
- Where it grows: Stone surfaces, glass panels, solar panels, signage.
- What it looks like: A slippery, green film.
How fast it grows: Can appear in as little as 4–7 days. - Risks: Leads to surface degradation, creates slip hazards, and can accelerate mould growth if left untreated.
Black Algae
- Where it grows: Roof tiles, metal panels, painted facades.
- What it looks like: Dark streaks or blotchy patches—often mistaken for dirt.
- How fast it grows: Typically develops over 2–3 weeks.
- Risks: Causes staining and material breakdown, and may contribute to increased heat absorption on roof surfaces.
Lichens
- Where it grows: Terracotta tiles, timber beams, exposed concrete.
- What it looks like: Crusty patches in grey, green, or orange tones.
- How fast it grows: Slow to form—visible colonisation takes 3–6 months.
- Risks: Can cause long-term structural damage, especially on porous materials like sandstone or unsealed timber.
Why Early Intervention Matters
When caught early, mould and algae are relatively easy to remove. But the longer they’re left:
- The stronger they bond to surfaces
- The more they trap moisture, encouraging rot or rust
- The more likely they are to creep into interior spaces through vents or gaps
- The harder (and more expensive) they become to eliminate fully
Elevated growth, such as on 2nd-storey walls, high sails, or rooflines, often goes unnoticed until major discolouration or damage occurs – at which point traditional cleaning methods become labour-intensive, risky, or even impractical.
Health Risks of Ignoring It
Leaving exterior mould unchecked isn’t just a cosmetic issue. Over time, the spores released into the air can enter buildings through:
- Air conditioning systems
- Open windows or doors
- Micro-cracks in walls or roofing
The result? Increased exposure for occupants, staff, and customers—particularly harmful for:
- Children (especially in childcare centres and schools)
- The elderly
- Those with respiratory conditions like asthma
How WashDrones Solves It Effortlessly
WashDrones eliminates the access barrier. Our aerial drone system:
- Reaches heights safely and efficiently
- Applies Wet & Forget with precision, killing mould at the root
- Requires no scaffolding, boom lifts or rope access
- Leaves no mess, thanks to targeted spray coverage
- Keeps your building protected for up to a year with our ongoing maintenance plans
Whether it’s a school shade sail, a club’s signage facade, or a hospital awning, WashDrones makes it easy to stay ahead of the growth cycle and maintain your assets without disruption.
Stop Looking Up and Hoping It Goes Away
If you’ve noticed mould, algae or black streaking on elevated surfaces in your area, it won’t get better on its own.
WashDrones offers a fast, cost-effective way to remove and prevent regrowth—with zero downtime and complete safety from the ground up.
Get in touch to book a free aerial inspection or schedule a mould prevention clean today.
