Introduction
Dark spots, stains, and damaged walls often raise doubts: is it mould or rising damp? Although both are linked to moisture, their causes and signs are different. Understanding the distinction helps avoid confusion and makes it clearer which type of damp is present.
What is mould?
Mould is a fungus that grows in humid and poorly ventilated environments.
- Appears as black, green, or grey patches.
- Found on surfaces such as paint, wallpaper, or wood.
- Strongly associated with condensation.
Typical signs of mould:
- Spots in corners, ceilings, or behind furniture.
- Musty smell that persists.
- Rapid growth in bathrooms and kitchens.
What is rising damp?
Rising damp occurs when groundwater moves upward through the wall by capillary action.
- Mainly affects the lower part of walls.
- Carries salts that form white deposits (efflorescence).
- Independent of ventilation habits.
Typical signs of rising damp:
- Stains at the base of walls.
- White, powdery salt marks.
- Flaking paint or plaster near skirting boards.
Key differences between mould and rising damp
| Feature | Mould | Rising damp |
|---|---|---|
| Cause | Condensation, poor ventilation | Groundwater moving upward |
| Location | Corners, ceilings, cold spots | Lower wall areas (up to 1m) |
| Appearance | Black/green/grey spots | Yellow/brown stains + salts |
| Smell | Musty, fungal odour | Damp smell, more neutral |
| Growth speed | Rapid under humidity | Slow, progressive |
Why the distinction matters
- Mould: linked to condensation → improved ventilation and heating habits often help.
- Rising damp: originates in the ground → requires measures that act on the wall and moisture source.
- Mixing them up can lead to ineffective actions and wasted costs.
Conclusion
Although mould and rising damp may look similar, their origins and symptoms are not the same. Mould is caused by condensation and grows in patches, while rising damp appears at the base of walls with efflorescence and flaking finishes. Recognising the differences is the first step towards understanding which type of moisture affects a building.
