Why Humidity and Rainfall Cause Cement Block Walls to Grow Black Mould

In The Gambia and other tropical regions, humidity and heavy seasonal rainfall create the perfect environment for mould and mildew growth on cement block walls. While cement blocks are widely used due to their affordability, they have a natural weakness: porosity. Cement blocks contain tiny air pockets that easily absorb and retain moisture.

When the rainy season arrives, walls soak up water like a sponge. Even after the rain stops, high humidity in the air slows the drying process. This constant dampness becomes the breeding ground for mould and algae. Black mould spores, already present in the air, settle onto the damp surface and quickly multiply.

The issue is not just aesthetic. Black mould stains walls, makes buildings look old long before their time, and creates ongoing maintenance costs as owners must repaint, scrub, or re-plaster. Over the years, this cycle of water absorption and mould growth also weakens the structural integrity of the blocks, as moisture encourages micro-cracks and erosion.

Solutions include:

  • Using Eco Interlocking Earth Blocks (CIEBs) which are denser and naturally regulate moisture.
  • Applying breathable but water-resistant finishes that repel rain while allowing walls to “breathe.”
  • Designing houses with wide roof overhangs and proper drainage to reduce direct water exposure.

Humidity and rainfall are natural realities in The Gambia, but with smarter building practices, walls can stay dry, clean, and long-lasting.

info

Humidity and rainfall are natural realities in The Gambia, but with smarter building practices, walls can stay dry, clean, and long-lasting.