This may sound like a peculiar question to ask, but if the answer is no then this may result in it being very costly.
The chimney stack is one of the most exposed areas of the property and is also one of the most neglected when it comes to maintain. Water ingress into any part of the structure will be detrimental resulting in dampness and decay.
Water entering a chimney structure will result in dampness further down within the building structure resulting in what is termed salt dampness ‘The movement of hygroscopic organic salts into the plaster surface’ this results in staining, dampness and de-lamination of the applied plaster.
Water ingress into the chimney structure will also result in the bearing timbers of the roof structure being affected by fungal decay.
These salts remain at the surface and their hygroscopic effect will continue. A characteristic of this is that on some days the wall surface will appear dry yet on other days, subject to the weather, damp patches will appear and be damp to the touch. The cause of this is not necessarily additional moisture ingress but purely the hygroscopic salts absorbing moisture from the atmosphere.
The first course of action should be to prevent further water ingress into the structure, by overhauling the external chimney stacks, and were required dismantling and rebuilding. When undertaking this type of work it is imperative that the ‘working at height and health and safety and work regulations are followed, and that scaffolding is erected to form a safe working platform and also ensure that the works are undertaken to a good standard.
The most effective way to counteract the action of hygroscopic salt contamination to the internal wall area is to physically remove the contaminated plaster that contains the salts. It is also very important that the re-plastering specification prevents any further salts present in the brickwork, from migrating through to the new decorative surface.
When the plaster is removed a cavity plaster membrane should then be installed to the wall held in place with plastic fixing studs, if possible this should be taken up behind the ceiling line to prevent cross contamination by the salts into the ceiling line.
A dry lining or wet plaster system can then be applied to provide a dry salt free decorative finish to the internal chimney breast structure.
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