Laboratory test to assess sensitivity of bio-based earth materials to fungal growth

The effect of molds present in buildings on the health of the occupants is a major issue hence, when a building material is developed, its sensitivity to microbial growth should be assessed. However, few studies have investigated fungal growth on bio-based building materials with the resources available in a laboratory specializing in materials. The objective of this paper is thus to propose a simple and efficient experimental method useful for construction materials laboratories, adapted from methods proposed in the literature. For this purpose, fungal growth was investigated under different environmental conditions on earth-based material with or without the addition of straw or hemp shiv. Samples were inoculated with a strain of Aspergillus brasiliensis and were incubated for 12 weeks at 76, 84 or 93% RH, and 30 °C or 20 °C. Reproducible results showed that earth-based materials were more sensitive to fungi when they were enriched in plant aggregates. Fungal development was observed on earth material containing plant aggregates after 4 weeks of exposure at 93% RH and 30 °C, whereas it was observed after 8 weeks on raw earth material under the same conditions. Additionally, the possibility of quantifying fungal development with increased sensitivity by using image analysis is proposed. Due to the growth of fungal species other than A. brasiliensis, a natural inoculation approach is recommended. One of the conclusions is that liquid water is more favorable to mold growth than relative humidity alone. The addition of liquid water is thus recommended to accelerate the test.