There are three main types of damp and each type needs to be treated differently. The costs of treating damp can vary considerably so it is important to know which type damp is affecting your home. In this blog post Blount and Maslin describe the types of damp you may encounter in your property.
Rising damp has been an issue for hundreds of years, there is strong evidence suggesting it was understood by Romans and ancient Greeks. The problem of damp rising up walls was addressed by the Roman architect Vitruvius, who advised on how to erect buildings to avoid the problem.
So, what is rising damp?
- Rising damp is the slow upward movement of water that creeps up walls, and sometimes floors, by capillary action.
- Rising damp occurs when ground water travels upwards through porous building materials such as brick, sandstone and mortar.
- Rising damp is commonly seen at the base of walls. It can be identified by the presence of a tide mark caused by soluble salts (particularly nitrates and chlorides) that tend to be contained in the ground water. These salts accumulate at the peak of the rising damp and become white salt efflorescence as the wall dries.
- Rising damp typically has a low height and rarely is above 1.5m.
- Rising damp is far less common than perceived and is often misdiagnosed.
Penetrating damp occurs when water passes through the external material of the building and saturates the wall. The water often becomes contaminated resulting in a brown stain on the internal surface of the property. Penetrating damp can occur at any level and even damage at the base of a wall is more likely to be caused by penetrating damp than by rising damp.
Penetrating damp is likely to occur when defects are present, including but not limited to:
- Cracks in masonry or rendering
- Roof defects such as faulty flashing, missing or cracked tiles or slates
- Missing or defective seals around windows and doors
- Blocked weep holes
- Missing or defective trays in cavity walls
- Holes in walls where cables or pipes protrude
- Location/aspect of wall – e.g. walls facing prevailing wind are more prone to penetrating damp
- Defective or blocked rainwater goods
Condensation occurs when water vapour within warm internal air meets a cold surface, this encourages the water vapour to convert into its original liquid form.
- Damp due to condensation is common in poorly ventilated rooms and particularly in rooms with a high moisture content, for example kitchens and bathrooms.
- Common sources of water vapour include bathing and cooking. When this moisture is not addressed quickly enough mildew and mould occur.
- In the UK problems with condensation are very common between October and March as at these times the walls are much colder than the air inside.
- Condensation is often provoked by other forms of damp that result in the external wall being cold.
- Damp caused by condensation will appear as black speckled marks or grey growths.
- Interstitial condensation can also occur, this is when condensation forms within the wall itself. Buildings with poorly insulated walls are very prone to this. Interstitial condensation causes damage that looks very similar to penetrating damp and often occurs in similar places.