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A guide to condensation, damp and mould

What are the three main causes of damp and mould?

1. Condensation

Cooking, washing, drying clothes indoors, even breathing can potentially cause condensation.

The first sign of a problem is water vapour condensing on windows and other cold surfaces, which then takes a long time to disappear, allowing surfaces to become damp. The second indication is black mould patches growing on these damp areas.

The 'amount' of condensation in a home depends upon three factors:

  1. how much water vapour is produced by the actions of its residents
  2. how cold or warm the property is
  3. how much air circulation (ventilation) there is

2. Damp - water leak

Damp can be caused by water coming through external walls or the roof. It can also happen when there is an internal leak or plumbing problem.

This can be caused by:

  • missing pointing
  • cracked rendering
  • missing roof tiles or defective rainwater goods
  • cracked water pipes, internal and external

Black mould is rarely seen on this type of dampness. This is because the affected area is usually too wet and the dampness contains salts or cleaning chemicals, will prevent mould growth.

3. Rising Damp

Caused by water rising from the due to a broken damp proof course (DPC) or passing through the natural brickwork if the property has no DPC. Usually only affects basements and ground floor rooms. It will normally rise no more than 12 to 24 inches above ground level and usually leaves a 'tide mark' low on the wall. If left untreated it may cause wall plaster to crumble and paper to lift.

Black mould will not usually be seen where there is rising damp. This is because rising dampness carries with it ground salts which prevent the growth of black mould.

Last modified on 16 November 2023

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