Damp is more likely to occur in properties that have undergone change since their original design. This change could be rapid such as the building of an extension or water leak, or slow such as weathered tiles or the building-up of ground levels.
Changes include modifications to the neighbouring properties and surroundings. We often spend time comparing the property to its neighbours, to help identify changes. The interface between new and old is a starting point for tracing dampness.
Damp meters are useful for rapidly identifying potential damp. Commercially available damp meters either measure dampness in wood by means of electrical conductance or by capacitance. Manufacturers advise against using meters for quantifying damp in anything other than timber. Pure water (sometimes referred to as de-ionised water) is a very poor conductor of electricity. Electrical conductance is a function of ions and cations, mainly from salts, and their mobility, which is increased by a carrier solvent such as water. Conductance of ions is used as a proxy for identifying water. This is justifiable in wood where salt levels are constant and quantified. However, damp in masonry can have a significant variation in the ionic components and concentrations of salts. Therefore, electrical conductance meters cannotpositively identify the type of dampnor the amount of dampness in walls. Damp meters can onlyidentify dryness.
Damp meters are useful for quickly identifying potential areas of dampness that need further investigation.
Assessing whether a high meter reading is a sign of dampness
Once a high meter reading is found we check the surrounding area to establish the extent and profile of the damp.
Condensation is the most common form of damp. The damp patches tend to be considerably cooler than the ambient temperature. Damp tends to start at the base of an exterior wall, particularly cool, shaded or North facing walls. It often has a curved profile, rising into a corner, and collecting around cold spots such as windows, metal electrical boxes, wires, pipes and corner beading. Condensation rarely affects skirting or floorboards, as wood is a poor conductor of heat. Walls may feel wet and smell musky. Mould can grow on walls, and on shoes and clothing.
Identifying the source of dampness
If the profile fits with condensation, then there is no need for further investigation. Leaks and water ingress are also easy to identify, but not always easy to trace.
If there is doubt about the damp source, we analyse a sample of the water for salt content.