Photograph showing rising damp and subsequent salt attack below DPC level.
Rising damp is destructive for buildings. It is well understood that damp very quickly will create rot in structural timbers such as bearers and joists, and therefore a DPC (damp proof course) is provided to prevent rising damp. A modern DPC is typically a black embossed polythene roll that is laid out directly beneath ant-capping, or just below finished ground floor level. Polyethelene underlay (black or orange plastic) serves the same purpose for slab on ground construction.
What is not usually considered, is that rising damp can also have destructive consequences for masonry below the DPC. Bricks used below the DPC should always be exposure grade, meaning they have been tested and certified to resist salt attack. Bricks that have extremely low porosity (i.e. water repellent) or that otherwise a large pore structure (large spaces that are unaffected by the 'heave' of expanding salt crystals) are the two ways that masonry can be made salt resistant.
Where does the salt come from?
It should always be assumed that salt is present in soil. Salinity is a growing problem in Australia due to factors such as the removal of trees for housing estates, and artificial irrigation that results in a rising water table. Common garden fertilisers used around a home garden can also contribute to introducing more salts into a sub-floor masonry wall. Each time that salt in the pores of masonry transition from a solution to a crystal, it can exert pressure in excess of 200MPa. The tensile strength of even high quality concrete is only about 10MPa, so it's easy to see why masonry can suffer aggressive decay.
So how can Efflock be used to control rising damp and salt attack?
Photograph showing rising damp damage to painted and rendered exterior wall. (Building only 8 years old).
Older houses and heritage buildings:
When mortar is missing from an old brick wall it seems perfectly logical to re-point the wall with a durable cement mortar - right? In fact that is exactly what should not be done or else much worse damage will follow. If the mortar is made to be more durable than the brick, then the bricks will become the sacrificial material. Lime mortar in old buildings acts to protect the brick or masonry units from decay. This is because lime is hygroscopic, so it attracts the salt damp and becomes the sacrificial material. Older buildings should only ever be re-pointed with lime mortar, and repeated every number of years as part of the building's maintenance schedule.
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