Why Important
Signs of dampness on a chimney breast suggests a structural problem with the chimney structure, or a significant lack of air flow within the chimney.
What to look for
Condensation within a flue, bringing hygroscopic salts and tar to the surface, can cause damp patches on the chimney breast and, in some cases, on larger areas of wall.
When to look
When the initial detailed survey is undertaken. Collect photographs of the existing situation.
Undertake annual inspections or when the building has a change of use/occupancy.
How to fix
In mild cases, sealing the wall with aluminium paint, applied once the plaster has dried out, will hold back the stain and permit re-decoration.
Otherwise it may be necessary to strip and re-plaster the chimney breast and line the flue with an impervious lining.
To avoid condensation and damage to chimneys, all flues serving gas fires and gas boilers should be lined with flexible non-ferrous metal liners.
Disused flues should always be ventilated at the top and bottom. Information on suitable clay vent terminals for use with chimneypots may be available.
Avoiding creating problems
Don’t block chimneys completely. Leave a vent for flow of air.