What Is Really Growing on Your Walls
Most people assume the staining on exterior walls is dirt, pollution, or general weathering.
In reality, it is usually a living layer of biological growth.
This layer is made up of four main organisms:
- Algae
- Fungus
- Lichen
- Moss
Together, they form what is known as biomass growth.
It starts with algae
Algae is the starting point for almost all exterior staining.
It is carried in the air and settles on surfaces where there is:
- moisture
- shelter
- microscopic surface texture
Once established, algae forms a thin layer across the surface. This layer allows other organisms to develop.
As outlined in our guide, algae acts as the base of the system, supporting the growth of fungus, lichen and moss.
Red algae as seen under a microscope
What happens next
Once algae is present:
- Fungus feeds on organic material, including dead algae
- Lichen forms from a combination of algae and fungus
- Moss grows in damp conditions supported by this environment
Over time, this results in:
- discolouration
- trapped moisture
- gradual surface deterioration
Why it matters
Biomass growth is not just cosmetic.
It can:
- hold moisture against surfaces
- contribute to material breakdown
- make surfaces slippery and unsafe
- obscure the natural appearance of stone and render
Why traditional cleaning fails
Many cleaning methods treat the problem as dirt.
Powerwashing is never a good solution.
This leads to:
- pressure washing
- abrasive methods
- harsh chemical use
These approaches:
- do not address the underlying biology
- can damage the surface
- often make the problem return faster
The correct approach
The key is to treat the cause, not the symptom.
A pH-neutral exterior treatment works by:
- targeting the algae
- compromising its cell wall
- stopping the biological cycle
Once the algae is no longer active:
- the remaining growth dies off
- natural weathering gradually removes it
This is not an instant process, but it is the correct and non-damaging approach.
A different way of looking at it
Instead of thinking:
“My walls are dirty”
It is more accurate to think:
“There is biological growth on my walls”
Understanding this changes how the problem should be treated.
Conclusion
The staining on exterior surfaces is usually not dirt.
It is a living system that starts with algae and develops over time.
Treating it properly means:
- understanding what is happening
- using methods that work with the surface
- avoiding damage
If you are unsure what is growing on your property, you can contact us for advice.