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Identifying Dampness in Buildings

Dampness can take many forms. It is not unusual for so called experts to mistakenly identify any dampness as rising damp. Similarly, there are many situations where contractors will specify repairs that do not solve the problem. If in doubt, consult an independent Building Consultant.

The main causes of building dampness are, rising damp, rain penetration, leaks, blocked spoutings and downpipes, bathroom leaks, condensation and mould, lack of sub-floor ventilation or lack of external membranes in below ground construction.

  1. Rising Damp first appears as a damp tide mark along the bottom of walls. Gradually small bubbles grow in the paint work or sections of paint start flaking from the walls. Left unchecked, the render and plaster beneath the paint starts to lose strength and can fall from the walls. On bare walls, mortar joints start to fret away and whitish coloured salt crystals appear. It is the salts that rise in solution with moisture that causes most of the damage.
  2. Penetrating Damp from rain is more common in older buildings with solid brick walls (no cavity) exposed to the weather. The appearance of moisture marks and bubbling paint will be more scattered over the wall. Consistent wind blown rain easily penetrates old brick work.
  3. External Water leaks from down pipes and spoutings appear as more pronounced damp marks that extent from floor to ceiling. Where rising damp will extend further sideways than up, leaks are higher than wide. There is often a yellowish tinge to the salts from the mortar as they cause distinct bubbling to the wall. This is an indication of excessive moisture penetration.
  4. Bathroom Leaks cause concentrated areas of damp. These areas will be behind leaking tiling or tap fittings. The most common is leaks behind tap fittings where the tap hole is not filled or the tap spindle leaks. The damp mark is always dark and yellowish again showing excessive water penetration.
  5. Condensation leads to mould growth. Mould appears as fine dark spots on walls and ceilings. In all cases there is no damage to the wall surface and the mould can be washed off. It appears most often in the colder winter months when internally generated water vapour cools on the coldest surfaces in a building. It is not a structural problem. It can be classed as a lifestyle problem as the moisture is generated from activities within the building such as washing and drying clothes. A dehumidifier is a good help, but understanding the problem is of greater benefit. Many on line articles are available on this subject.
  6. Sub Floor Ventilation is important to keep the air below timber floors dry. If ventilation is inadequate, the air becomes musty. The musty air can make it’s way into a building through gaps between floors and walls around skirting boards and up through wall cavities into wall vents which creates the musty smell. In extreme cases, condensation will occur beneath the floor and cause rotting of floorboards. Lack of ventilation does not cause rising damp or be a sign of rising damp. It is a separate issue, but can be a contributing factor with internal condensation and stains on the edges of carpets.
  7. Below Ground dampness is the result of poor or perished external water proof membranes where rooms are built into the ground or on slopes. Over time, outside conditions change and drainage systems can block. Also, during construction, if the rooms were called up as store rooms, the same level of care to water proofing was not applied as if the rooms were classed as ‘habitable’. This is particularly the case in garages and where rooms have changed usages. Heavy salting will appear on walls and moisture levels in the wall will be high. If there are water leaks, the drains may have to be cleaned out and a new membrane installed. This can become a very expensive exercise.