Chimney damp

Fix that damp chimney for Christmas!

admin Damp

Only 13 more sleeps until Christmas! The big day is nearly here – so think of Santa and sort out that damp chimney!

Chimneys are more exposed than any other part of a building, so it’s no surprise that they frequently suffer from damp.

Chimney damp has various causes, including rain (which can come down the flue of an uncapped chimney), condensation (burning fuel produces water vapour) and salt contamination in the plaster (common in older chimneys where coal was burnt over many years).

Rain penetration is a common cause of chimney dampness. This can be as a result of an uncapped chimney pot, or perhaps defective lead flashings around the chimney stack. Sometimes it’s due to a defect on guttering or downpipes.

If you have a broken gutter, for example, a heavy downpour can result in water running down the exterior wall and seeping into any cracks in the mortar. In a rainy location (hello northern Britain), the simple occurrence of lots of water frequently running down your walls can, over time, cause your chimney to become damp.

If you share a chimney with neighbours, it’s worth having a chat with them about any work they have carried out which may be the cause of your damp chimney. For example, they may have fitted a wood burner without the correct flue, or perhaps blocked up internal ventilation. A friendly conversation can quickly rule in or out any possible causes of damp.

Before any damp issue can be put right, the source of the leak or moisture must be located and repaired. If the origin of the problem is not completely fixed, then any repairs will be short lived, wasting the time that it has taken to fix the damage and also any money spent, as a few months later you will just have to do it all over again.

However… even when the underlying source of dampness has been fixed, damp patches on chimney breasts can remain. This is because most chimney breasts are contaminated with moisture-attracting hygroscopic salts that have accumulated over many decades.

Salt contamination of chimneys is as a result of fossil fuels like coal being burnt in the fireplace over many years. Coal contains salt minerals like nitrates, chlorides and sulphates. When the coal is burnt, these salts manifest themselves in the brickwork of the fireplace. Over time, and especially if the fireplace is no longer used, the salts can migrate from the brickwork and settle in the wall plaster. These salts then become what is known as ‘hygroscopic’, which means that they attract and hold moisture from the surrounding environment. This is why the damp patches associated with salt contamination are often worse when the weather is.

Trying to solve the problem by simply repainting or replastering using a standard gypsum plaster will not normally be effective in these situations, as the hygroscopic salts will simply migrate to the surface and the damp patches will reappear.

Multiskill has over 50 years of experience in the diagnosis and treatment of chimney damp as well as other types of damp, like rising damp, penetrating damp and condensation. We can advise on the cause and the most effective solution for any chimney dampness problem.

If you want to keep Santa happy this Christmas, get in touch for diagnosis and a quote.