Conducting a microbiological investigation
Our recent project was a mansion building situated in Dorking. Our client instructed us to carry out a building inspection and microbiological sampling and to evaluate the presence of suspected fungal contamination to the external rendering of the building.
The mansion is a three-storey building with rendered traditional stone walls and a flat roof. The property is situated in a parkland and is surrounded by mature vegetation and grassland. At the time of our inspection, the property was currently undergoing extensive refurbishments with internal areas of the property at various stages of completion. The external rendering to the building was complete although there were sections of scaffolding present to the East, South and west side of the building.
What is microbiological sampling and what did it reveal?
Microbiological sampling involves taking samples of surface materials for the evaluation of fungal contamination. A visual inspection of the property revealed that the surface of the rendering is currently affected by black to grey discolouration in several places. The external cornices and roof top rendering to the perimeter and internal walls, appeared to be the areas most affected by discolouration. This discolouration and black spots are prevalent on the plasterboard insulated sections of the rendering but were also observed on other parts of the walls, though in lesser quantities.
Further inspection of the discolouration revealed that the walls were affected by two types of particles. The lower sections of the walls were mostly discoloured due to the presence of black angular particles. Samples from these areas were analysed under a microscope (see image below) which confirmed that the particles are bituminous and are soluble in solvents. A small proportion of black to brown discoloured spots on the exposed parts of the walls is cause by trapped insects, plant detritus and larger inorganic dust.
On the external cornices of the building, patchy black to brown discoloration was also identified. These areas of discolouration were analysed under a microscope which confirmed the presence of fungal hyphae and fungal spores. The fungal species colonising the rendering was identified as Alternaria mould and this mould growth was observed on the surfaces below the layer of the newly applied render and also on the surface layer of the rendering with minimal penetration through the rendering.
What did we conclude and recommend?
As a result of microbiological sampling we were able to conclude that the external rendering of the building was affected by fungal growth. The fungal attack was being facilitated by the presence of moisture as well as an accumulation of a thin layer of dust. Our surveyor does not believe that the presence of mature vegetation in close proximity to the building has any effect on the occurrence of the mould growth to the rendering.
We recommended our client to remove the affected sections of the rendering and decontaminate the area with the application of an antifungal treatment to the underlying layer of stone or polystyrene. It is important that this treatment is carried out in dry weather in order to allow adequate drying and it should be carried out immediately before the application of the rendering. The surface of the dried rendering should also be treated with the antifungal treatment.