Black Mould on Walls After Rain in Ghana — The 3 Real Causes and How to Stop It Permanently

Black mould on your interior walls is more than an eyesore. It releases microscopic spores into the air that trigger asthma attacks, allergic reactions, and respiratory infections — especially in children, elderly people, and anyone with existing lung conditions. Scrubbing it with bleach removes it for a week or two. Then it comes back, sometimes worse.

Black mould keeps coming back because it needs three things to grow: moisture, warmth, and an organic food source (paint, plaster, wallpaper glue). Ghana provides two of those in abundance — warmth and organic surfaces are always present. The only thing you can control is moisture.

The 3 Causes of Black Mould in Ghanaian Homes

Cause 1: Condensation Damp (By Far the Most Common)

When warm humid air inside your home hits a cold wall surface, water vapour condenses into liquid water. Repeated condensation soaks the wall, feeds mould growth. In Ghana, this happens most in:

• Corners of rooms against exterior walls
• Behind furniture pushed against exterior walls
• Ceiling corners in bathrooms and kitchens
• Bedroom walls behind wardrobes and beds
• Anywhere air circulation is poor

How to identify: Mould in room corners, behind furniture, in rooms with limited ventilation. Worst in wet season. No obvious water source.

Fix:

• Install extractor fans in bathrooms and kitchens — vented to outside, not into ceiling void
• Add trickle vents to bedroom windows
• Keep furniture 5 cm away from exterior walls
• Do not dry laundry indoors
• Insulate cold walls to raise their surface temperature above the dew point

Cause 2: Penetrating Damp (Water Coming Through the Wall)

Rain water tracks through a cracked exterior render, a failed window seal, or a leaking gutter into the wall cavity. The wall stays damp for weeks after the rain. Mould grows on the damp interior surface.

How to identify: Mould in a specific spot on an interior wall that corresponds to something on the outside — under a window, next to a downpipe, below the roof line. Mould worsens during and after heavy rain.

Fix: Locate and seal the exterior entry point. Apply an exterior wall waterproofing coat. Allow interior wall to dry fully (4–12 weeks). Treat the affected area with an anti-mould primer before repainting.

Cause 3: Rising Damp (Bottom of Wall)

Groundwater is drawn up through the wall by capillary action. Where the wall stays damp above the ground line, mould grows.

How to identify: Mould concentrated on the lower 30–100 cm of a wall, often exterior walls or ground-floor rooms. Sometimes accompanied by white salt deposits (efflorescence). See our efflorescence guide.

Fix: Chemical DPC injection. Salt-neutralising re-plaster. Anti-mould primer + breathable finish. See our full damp walls guide.

Why Bleach Doesn’t Work

Chlorine bleach kills the visible mould on the surface. But the mould has already grown roots (hyphae) into the porous plaster underneath. Within days, new spores germinate from the surviving roots and the black patch returns.

Bleach also does nothing about the underlying moisture. As long as water keeps reaching the wall, mould keeps growing.

The Correct Mould Removal Process

1. Fix the moisture source (condensation, penetrating damp, or rising damp — identified above)
2. Let the wall dry fully (4–12 weeks depending on cause)
3. Scrub off visible mould with a fungicidal wash (not bleach)
4. Apply an anti-mould primer to the affected area
5. Repaint with a breathable emulsion containing fungicide additive

Health Warning

If anyone in your household has asthma, allergies, or respiratory conditions, black mould is not a maintenance issue — it is a health emergency. Prolonged exposure to indoor mould has been linked to:

• Chronic cough and respiratory infections
• Sinus congestion and headaches
• Skin rashes and eye irritation
• Worsening asthma symptoms
• Sleep disturbance from congestion

Deal with it promptly. Your family’s health depends on it.

Get a Free Mould Assessment

• Phone: 0555 548 001 or 0241 737 026
• WhatsApp: Send us photos of the mould
• Related: Damp Walls Guide · Peeling Paint

Festghana Waterproofing Solution Company Limited provides mould remediation, damp treatment, and moisture control services across Ghana. Workmanship warranty on every job.