Are you roofed in right ?


Property Remedial Articles - Olympic Construction

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.

During this inspection we noted evidence of well-established weed within the mortar beds of the shared chimney structure, this indicates that the mortar beds are both porous and friable allowing the root system of the weed to become well established. It has also been found where weed growth has become well established the root system, will have passed deep into the mortar bed and into the chimney flues, resulting in the flues becoming blocked and unstable. In this case re-pointing will be ineffective at stabilising the chimney structure and it will continue to move, resulting in further water ingress and weed becoming re-established, resulting in the dismantling and reconstruction of the chimney stack being required.
chimney stack

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.

damp room
The salts are deposited within the structure by the soot, as a by-product from the burning of coal, the salts of concern are ammonium chloride and nitrate. These salts are what are termed hygroscopic, which means they have the ability to absorb moisture from the atmosphere. In the event of moisture penetrating a chimney flue from external defects in sufficient quantities will often find its way through to the decorative surface. Salts are only able to move in solution and when such a leak occurs within the chimney structure, these salts are transmitted from the flue lining through to the decorative surface from where the water which transported them evaporates.

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.

Remedial Works 

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.

Copyright protected by Olympic Construction 2013.