The Role of Airborne Spores in Mould and Algae Growth on Buildings

Many homeowners are surprised when freshly painted walls develop black or green patches within just a year or two. The culprit is often airborne spores — microscopic seeds of mould and algae that float invisibly in the air.

In humid climates like The Gambia, spores are everywhere: carried by the wind, deposited by rain, or even spread from nearby trees and plants. The spores themselves are harmless when dry, but once they land on a damp cement block wall, they find the ideal conditions to grow.

Cement blocks, being porous, stay damp long after rainfall. Combined with warm temperatures and humidity, this creates the perfect “nursery” for mould and algae. That’s why you often see mould spreading in shaded, less-ventilated areas such as north-facing walls or corners where air circulation is poor.

The risks of airborne spores:

  • They spread quickly, meaning once mould starts in one spot, it can easily spread across an entire wall.
  • They worsen indoor air quality if mould penetrates inside, leading to allergies, asthma, and respiratory issues.
  • They weaken surface finishes, causing paint and plaster to bubble, crack, and peel.

Preventive measures include:

  • Building with denser materials like CIEBs that absorb far less moisture.
  • Applying anti-fungal and anti-algae coatings on exterior walls.
  • Improving ventilation around the house to ensure walls dry faster after rainfall.
  • Designing with landscaping in mind — for example, trimming vegetation close to walls, since plants increase airborne spores.
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By understanding the invisible role of airborne spores, homeowners and builders can take smarter steps to protect walls, reduce maintenance costs, and create healthier living environments.