The damp conditions in homes and properties encourages the growth of micro-organisms in particular black mould on the walls
The mould then begin to spread from the source of the dampness to regions where there is less dampness by releasing spores into the atmosphere. These airborne spores are thought to be inhaled by unsuspecting household occupiers. These spores that are thought to be linked and coincide with the increased number of residents suffering from respiratory illnesses and who are living in damp property according to a Finish study endorsed a member of the British Thoracic Society, Dr John Harvey. Examples of respiratory illnesses being asthma,bronchitis and pneumonia.
Fig.1: mould growing on a wall:
In this study, it was found that people who suffered from colds, tonsilitis, bronchitis, pneumonia suffered far more frequently in damp housing conditions than in non-damp housing conditions and people were more at risk of developing asthma,bronchitis and pneumonia in damp housing conditions.
This health issue clearly shows the importance of having a house or property externally rendered as the render prevents moisture from entering the building by being durable enough not to crack as well as preventing water accumulating within the structure.
There are 2 main types of damp problems that occur in buildings which encourage the growth of mould, these two types being penetrating damp and rising damp which can lead to serious problems such as the health problems associated with the mould.
Rising damp is literally damp that rises from ground level of the property to a level of about roughly 120 cm. This distance is determined by factors such as partially to do with gravity, pressure exerted by the weather and also the level of the water table. (The water table is the level of water’s distance halfway between the ground level to the upper level of the wall surface and at which point the ground water pressure is equal to atmospheric pressure, and can vary according to local climatic conditions and also the time of year.)
Rising damp occurs when the DPC (damp proof course) i.e. a horizontal barrier that is designed to prevent the moisture from the ground rising has either failed or doesnt exist at all.
Fig.2: what DPC looks like:
The DPC is a layer composed of a material that resists water to pass through it, this material being either bitumen (a large hydrocarbon molecule obtained from heated crude oil), polyethylene ( a large self repeating molecule derived from the same basic starting material which is ethene), metal sheets etc. The DPC should be installed rough;y 150mm – 200mm above exterior ground level. If floorboards are to be used, the DPC layer should be placed below this internal floor. If the building’s internal floor is solid, then the DPC should be placed a small distance below this wall.
Penetrating damp is the second type of damp caused by bricks falling off the exterior walls, cracking in the exterior render/ pebbledash or the fragments of bricks being blown off by the force of strong winds which allow water to enter and remain in the brickwork or substrate. This in turn can form small cavities behind the exterior wall surface which gradually fill up with water. During the winter season, the accumulated water freezes and expands into one of its physical forms which is ice and this increases the size of the cavity and allows for more water to get into the wall. In extreme cases, if the loose or hollow render is not dealt with and repaired quickly, it can fall off.
Penetrating damp can be distinguished from rising damp due to penetrating damp being able to appear anywhere within your house (hence the name penetrating) whereas rising damp typically occurs roughly 4 feet from the ground (hence the name rising damp).
Solution to mould infestation
If black mould is found inside your house or property, the short term solution would be to use an anti fungal treatment or damp wall treatment is required to remove the organism. After this is done, the long term solution would be to locate the source of the dampness and have it repaired to stop mould from growing again. Once the source of the dampness has been located,external rendering materials are to be used such as exterior spray applied wallcoatings and waterproof resin based wall finishes.