Mould on building materials - A calorimetric study of fungal activity as a function of environmental factors

Abstract: Mould problems in buildings have become a growing concern during the past decades. The growth of mould fungi indoors deteriorates air quality, influences human health and causes economical losses. Preventing mould growth from occurring is a more cost effective option than cleaning and renovation of buildings with mould problems.

Mould growth will occur in buildings when there are moisture problems. Many constructions have various defects that cause high humidity or even condensation on cold surfaces. Some of these defects are avoidable and can be corrected at the design stage. A calculation tool and knowledge of mould growth behaviour as a function of environmental parameters are therefore needed to predict the risk of mould growth for building design. The aim of this project was to study mould behaviour on building materials as a function of environmental parameters, such as temperature and relative humidity and therefore to serve as a tool for preventing mould problems in buildings.

Isothermal calorimetry is the main method used in this project to quantify mould activity. This method has not been applied much in fungal studies. Therefore it was tested and investigated to increase the understanding of the information that could be obtained from such measurements. Calorespirometry experiments (simultaneous calorimetry and respirometry) have been done on several mould fungi as well as on one rot fungus for understanding the correlation between fungal respiration and their heat production. Calorimetry was also compared with some traditional methods used in studying fungal growth by comparing heat produced by mould fungi with its biomass and ergosterol content. This also gave an increased understanding of fungal growth mechanisms. The results proved that calorimetry can not only be used on its own but can also be combined with other techniques to study fungal physiology.

The impact of temperature on mould growth was studied by comparing the produced heat, biomass and ergosterol of mould at five different temperature levels. Mould growth is highly influenced by temperature and this study also showed that the temperature at which that mould has the most rapid growth is not necessary the temperature at which it has its most efficient growth. This finding reveals the complexity of the influence of temperature on the fungal metabolism.

The influence of relative humidity on mould was also studied by measuring the fungal activities of mould growing on wood at different relative humidities. The results showed that although mould activities decreased when the relative humidity was low, too high relative humidity could also seem to inhibit part of its activity. Not only relative humidity but also moisture content is an important factor influencing mould activity. However the interpretation of these measurements was complicated by transient effects.

Mould growth development on wood, which were dried and treated at different temperatures was also studied by image analysis. All kiln-dried material exhibited higher mould growth levels than the air-dried material. Spruce heartwood had better resistance against mould growth than spruce sapwood. Heat-treated spruce had very low levels of mould growth. The measurements confirmed that nutrient transport to the drying surface increases the risk of mould growth there.