Noticed green stains spreading across your exterior walls?
That green build-up isn’t just dirt — it’s mould, algae, and organic growth. And in places like Auckland, it’s extremely common.
If left untreated, it can:
- Damage your home’s appearance
- Affect paint and surfaces
- Continue spreading over time
In this guide, we’ll explain:
- What that green mould actually is
- Why it grows on your house
- How to remove it properly
- And how to stop it coming back
What Is the Green Growth on Your Walls?
The green staining you see is usually a combination of:
- Algae
- Mould
- Mildew
👉 These organisms thrive in damp environments and attach themselves to your home’s exterior surfaces.
Why Green Mould Grows on Houses
1. Moisture & Humidity
Auckland has:
- High humidity
- Frequent rain
- Mild temperatures
👉 This creates the perfect environment for mould and algae to grow year-round.
2. Lack of Sunlight
Areas that don’t get much sun — such as:
- South-facing walls
- Behind fences or trees
- Under eaves
👉 Stay damp longer, allowing mould to develop.
3. Dirt & Organic Build-Up
Dust, pollen, and organic matter settle on your home.
👉 This becomes a food source for mould and algae.
4. Blocked Gutters & Water Runoff
Overflowing gutters can:
- Spill water down your walls
- Keep surfaces constantly wet
- Accelerate mould growth
👉 This is why issues like blocked gutters often contribute to staining.
5. Coastal Conditions
Homes near the coast deal with:
- Salt air
- Wind-blown moisture
👉 This increases surface dampness and speeds up growth.
Why It Keeps Coming Back
Many homeowners clean their house — only to see the mould return.
That’s because:
- Surface cleaning doesn’t kill spores
- The root cause isn’t treated
- Conditions remain the same
👉 This is why the problem repeats.
The Right Way to Remove Green Mould
❌ High-Pressure Cleaning
Water blasting may remove visible dirt but:
- Doesn’t kill mould at the root
- Can damage paint and cladding
- Leads to quick regrowth
✅ Soft Washing (Recommended)
Soft washing uses:
- Low-pressure cleaning
- Specialised treatment solution
This:
- Kills mould and algae at the root
- Prevents rapid regrowth
- Protects your home
👉 This is the safest and most effective method for exterior house cleaning.
How to Prevent Mould from Coming Back
While you can’t eliminate it completely, you can reduce it:
- Wash your house every 6–12 months
- Trim trees to increase sunlight
- Keep gutters clean
- Treat your roof to prevent moss spread
👉 Regular maintenance is key.
Signs Your House Needs Washing
Look for:
- Green staining on walls
- Black streaks under gutters
- Dull, dirty surfaces
- Mould in shaded areas
👉 If you see these, it’s time to act.
Professional House Washing in Auckland
A professional clean ensures:
- Proper treatment of mould and algae
- Safe, low-pressure cleaning
- Long-lasting results
👉 That’s why homeowners trust Metro Water Blasting for reliable exterior cleaning.
Get a Free Quote Today
If green mould is taking over your home, now is the time to deal with it properly.
👉 Visit your house washing Auckland service page
👉 Call: 0800 997 997
👉 Or fill out the form below for a free, no-obligation quote