DAMP PROOFING
Introduction to Dampness in Buildings
Dampness in buildings can be caused by defects to roof coverings, flashings, internal or external plumbing defects, heating and ventilation, external renders or the lack of an effective damp proof course, thus resulting in penetrating damp, condensation and rising damp. All of which ultimately can lead to the deterioration of the fabric of the building i.e. timber decay, defective internal and external wall finishes, brickwork, stone or mortar deterioration.
Identification of Dampness in Buildings
The use of an electrical moisture meter will only confirm that a level of dampness is present, analyzing the profile of the readings gives an indication of the type of dampness. In some cases samples of the structure, plaster and salts will need to be laboratory tested. Maclennan-LSE surveyors are able to test for salts on site and advise on the implications of the findings.
In conjunction with the meter readings taken the inspection will need to take into account the age and type of construction of the building, the geographical location, any defects that may be contributing to the damp problem i.e. rainwater, plumbing, roof coverings, external weathering, rendering, pointing and condensation.
Types of Dampness:
Penetrating DampWhere moisture from the external elevations penetrates through the structures of the building.
Condensation
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At any given temperature the air can hold a given amount of water vapour, the warmer the air the greater the amount of water vapour that can be held.
Should warm moisture laden air become cooled it reaches a temperature where it can no longer hold the water vapour. When this temperature is reached the air must release the water vapour; this is seen as condensation usually appearing as droplets of water on surfaces.
However, the most tell-tale sign of condensation is the frequently associated development of mould growth. The appearance of the mould may be black, white, yellow, green i colour, depending on the specific type of mould and the surface on which its growing.
Damp Proofing Methods:
For a long time now the chemical damp proof course has been seen as the cure for all damp problems. At Maclennan-LSE we specify and carry out work on a whole range of buildings. Many of them are traditional built buildings of cob and stone or flint and brick. For these buildings a chemical damp proof course is unsuitable.
The Maclennan-LSE Answer to the Problems:
Penetrating DampOur surveyors will look at all of the sources of moisture into the fabric of the building and discuss the affects of the moisture ingress the long term plans for the property and then propose the most suitable course of action for the building and the occupant.
- Maclennan-LSE Surveyor testing for salts
- We will recommend the correct repairs for the obvious defects.
- We will recommend on going maintenance.
- We can monitor the property confirm that it is drying or implement a drying solution and monitor to confirm that the source of ingress has been cured.
- In extreme cases we can Install external ventilated cavity membranes and render over them.
We might recommend the removal of sand cement renders and replacement with a lime render which will allow the walls to breathe and shed moisture. See this PDF document for more on lime render.
We Do Not Recommend:
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Too often we see brick faced houses coated with cement based applied coatings as a cure for penetrating damp. In most cases the houses are not even damp and have not been professionally checked. Cement based coatings can often cause problems.
We very rarely recommend any form of external spray applied siliconate treatment. It is rarely effective or necessary.
We very rarely recommend wholesale re-pointing. If mortar joints need chasing out then they do not need re-pointing. Most re-pointing is carried out with sand and cement.
If the house was built prior to 1900 it was almost certainly built with lime mortar. Pointing a traditional built house with cement can cause damp problems.
Maclennan-LSE would match existing lime mortars and carry out localised pointing if really necessary.
Maclennan-LSE Rising Damp.For buildings built with walls thicker than 400mm or of chalk, cob, flint or friable stone we would recommend ventilated cavity membranes (more information - PDF).
Cavity Membranes
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Ventilated cavity membranes allow buildings to 'breathe' by letting moisture vapour escape from the surface of the wall through a continuous air gap. They are a form of dry lining but as they are not made of a bio degradable material such as wood or paper ( on plasterboard ) they cannot decay and will last the lifetime of the building.
The inside of the property is left completely dry and warmer while the structure is breathing as it should do. There are a range of finishes that can be applied over the membranes. LSE plaster over with lime mortar plasters, High Impact one coat plaster and plasterboard adhered to the membrane, so as once plastered you would not know the wall had been lined.
We would not normally install a dpc as they are not very effective in this type or thickness of wall. Re-plastering has to be carried out with dpc injection to complete the damp proofing, The recommended plaster is a strong cement render which is not suitable for chalk or soft friable stone.
If dpc injection is to be installed in a thick stone wall then grouting or injection mortar would have to be considered.
An alternative to dpc injections is the Electro Osmosis system which LSE would be happy to discuss with you.
In ordinary brickwork walls up to 350mm thick we would consider a chemical dpc and re plastering to 500mm above the damp using a moisture and salt resistant plaster.
Silane CreamSilane cream is an injected DPC which is installed into brick built houses where an old DPC has failed or has been breached or was never installed.
