Don’t let Santa get damp – dealing with a damp chimney

Chimneys and flues are often subjected to intense cycles of hot and cold. With chimney stacks open to the elements, defects like damp can occur in chimneys that are used or redundant. This could be due to moisture and sulphates combining to form weak acids that attack lime, mortar joints and brickwork. Or it might be the moisture levels in a chimney have increased due to one end being sealed. Typically, however, the main causes of damp in chimneys are rain, condensation or salt contamination.

  • Rain can enter a chimney down the flue if chimney pots are uncapped, around defective lead flashings or through the wall of the chimney stack.
  • Condensation-based issues are more likely to occur in flues that remain in use as burning fuel produces water vapour.
  • Salt contamination in the plaster of a wall can also cause damp. This is more common in older chimneys and it can be the result of coal previously being burnt in the fireplace. Coal contains salt minerals like nitrates, chlorides and sulphates that can migrate from the brickwork into the wall plaster. These damp patches can often worsen when the weather does.

Coal burning in the fireplace

Identifying the cause of a damp chimney

It’s worthwhile trying to establish what the source of damp might be so the cause can be identified and treated accordingly. Things to check safely, and with the appropriate help, include:

  • Chimney stack – is it open-topped or capped? If it is open-topped it could be causing moisture to enter the chimney, travelling to the base of the stack. Damp around this area or in the brickwork is a tell tale sign. If your chimney stack is capped, make sure it has a well-ventilated cap or cowl to ensure there is no moisture build up.
  • Mortar – if the mortar around your chimney stack is cracked or splitting, water can get inside the chimney breast.
  • Lead flashing, tiles & loft space – the lead flashing on your roof, where it meets a wall or the chimney stack, should be checked to see if it’s coming apart or cracked. Similarly damaged tiles can also cause issues. Do look inside your loft space too to see if there are any signs of light coming in or if there’s a leak.
  • Guttering – gutters that are blocked cause rainwater to collect and can cause damp in your chimney. This is because water will be forced to run down a wall and seep into any mortar cracks.
  • Damp proof course – Have a look to see if your chimney breast has a damp proof course. This is a layer of slate or plastic a few inches above the ground, some older properties were built without these.

Air brick and damp proofing on the exterior of a house.

How to damp proof your chimney

Once you’ve identified the probable cause of damp in your chimney, it can be repaired. Damp proofing, dehumidifiers and anti-mould paint may temporarily combat a damp issue in your chimney but often it doesn’t provide a permanent solution. The Schrijver System, however, is a more effective and environmentally-friendly solution compared to traditional damp proofing and comes with a lifetime guarantee.

Installed by specialist engineers, the system uses natural ventilation to lower the humidity level and prevent damp. These experts install a series of small, handmade elements that are fixed to the outside of your property. These allow dry air to flow from the outside into the elements causing a drop in temperature and a ‘cold bridge’. This causes moisture from the wall interior to be deposited within the element and transporting the moisture outside.

Want to find out more about how Frank Schrijver can help you with your damp problems?

01689 800101