Fungal growth and survival in building materials under fluctuating moisture and temperature conditions

Growth and viability of fungi on three building materials under moistening and drying conditions were investigated in the laboratory. The materials were taken from buildings under repair and no additional inoculation of fungi was used. The materials underwent four treatments (4–8 weeks of each): capillary absorption of water, drying in air at a relative humidity (RH) of 30%, condensation and finally drying at 50% RH. Moisture content (MC), equilibrium relative humidity (ERH), and concentrations of culturable fungi, actinomycetes and total spores were determined in the materials at 1- or 2-week intervals. The results showed that when water was absorbed by capillary action to the materials, fungal growth started fast and was abundant in the wood-based materials with MC above 20%. Such a limit value could not be defined for fungal contamination in the gypsum board because of complex behaviour of moisture between the gypsum bulk and paper covering. The condensation under the varying RH and temperature conditions caused only restrained fungal growth in the materials. The fast drying (RH 30%) seemed to decrease the viability of fungi but along with the experiment fungal flora was modified to tolerate fluctuating conditions and the drying at RH 50% had only a slight effect on the viability of fungi.