Introduction to Dampness in Buildings:
For a long time now the chemical damp proof course has been seen as the cure for all damp problems. At Maclennan 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.
Our 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.
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. click here for more on lime render (PDF document)
We Do Not Recommend:
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 would match existing lime mortars and carry out localised pointing if really necessary.
For buildings built with walls thicker than 400mm or of chalk, cob, flint or friable stone we would recommend ventilated cavity membranes.
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.
Damp Proofing Methods:
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, before considering this read our advice on damp and lime render click here for PDF article on this subject.
MacLennan do have lime mortars that are damp resistant and are suitable for use on walls which are damp but where the cause of the damp has been cured. MacLennan lime plasterers have 20 years of experience with lime mortars and where they are suitable we will specify lime mortar for Historic buildings or buildings that need to “breathe”
For buildings built with walls thicker than 400mm or of chalk, cob, flint or friable stone we would recommend ventilated cavity plaster lath.
Ventilated cavity laths 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. Maclennan 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.’
Silane 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.