Mould infestation - searching with technology and a keen nose

Where and why does mould develop?

Mould develops in places where moisture and nutrients (organic material) are present. Additional ideal conditions for mould are temperatures in the range of 10-30 °C and poor air circulation. Mould problems often occur in connection with water damage or structural weaknesses (thermal bridges, leaks, etc.).

Airborne mould measurements - technical aid for mould detection

Airborne mould measurements are used as a well-known method for detecting mould. This method measures the number of mould spores in the air. It is important to know that the outside air always contains a number of mould spores, depending on the season, weather and vegetation. For this reason, a reference measurement must always be carried out outdoors for indoor air mould measurements so that the measurement results can be assessed.

The measurement procedure itself is not very complicated. The room being analysed should not be ventilated for at least one hour before the measurement. Using a so-called air sampler, a defined quantity (250 litres) of indoor or outdoor air is drawn in for a certain period of time and passed over a culture medium. These culture media are then sent to an external laboratory, which incubates the samples for 5-10 days at 25°C or 37°C and then analyses them. In principle, laboratories can carry out both quantitative and qualitative analyses. This means that not only the number of mould spores, but also the individual mould genera can be determined. Qualitative analysis is more time-consuming and expensive, but may allow conclusions to be drawn about the health hazards of the moulds present.

If the laboratory analyses indoors reveal a higher quantity of mould spores than the reference measurement outdoors, it can be assumed that there is a mould problem inside the room.

However, if mould infestation can be detected, the problem itself has not yet been solved. Where is the mould located? Do we need to take soundings of walls, ceilings or floors to find the mould? Another, less well-known method has been established for this purpose.

Photo: Dogs on a "guided" systematic search

Photo: Dogs "freely" searching for mould

Mould detection dogs - on the trail of mould with fine noses

Mould detection dogs can be used to locate mould infestation. Specially trained and constantly exercised dogs can detect mould with their excellent sense of smell.

During the search, a mould detection dog is let into the room and sets off on its own. For the search to be efficient and successful, the room must be properly prepared in advance, e.g. remove storage containers for leftover food or fruit trays, sweep the room clean and ventilate it (but close the windows one hour before the search) and make the structures and areas to be examined accessible.

Assumptions and prior knowledge about structures or neuralgic details can help to guide the dog during the search and to search certain areas systematically. The following video shows the procedure of a mould detection dog. If it can detect mould, it gives a clear signal. We had the pleasure of accompanying Claudia Erni, owner of Schimmelspürhunde Schweiz (https://schimmelspuerhunde-schweiz.ch), during a mould search.

The use of mould detection dogs gives no guarantee of being able to locate the mould and find all areas. A small, localised mould infestation may be easier for a dog to detect than a more extensive problem. Mould behind airtight structures cannot be detected by dogs. However, leaks in structures, e.g. in penetrations such as sockets, can be enough for dogs to detect mould.

The procedure is simple in principle, but the effort involved in training the dogs is very high and requires a lot of time and patience.

Mould found, what next?

If an infestation of the building structure with mould could be detected with the help of the mould detection dogs, the reasons for the infestation must be clarified (thermal bridges, water infiltration, etc.) so that an adequate remediation strategy can be determined.

In the case of extensive mould infestation, not only the mould itself but also the infested material must be removed. In the case of localised, minor infestation, the traces of mould can be easily removed with water and a standard household cleaner without any health concerns. If necessary, the area can then be disinfected with Javel water (aqueous hypochlorite solution) or 70-80% ethyl alcohol.

In the case of larger areas of infestation, the cause must always be thoroughly investigated and the infested areas professionally removed. The guide "Mould in living spaces, information for residents, tenants and landlords" (2021 edition) from the Federal Office of Public Health (FOPH) provides good guidance on how to proceed.

The exact remediation measures and their scope can only be defined after a detailed examination of the affected property and the collection of all relevant data.

We will be happy to help you with advice and assistance.