Determination of Critical Relative Humidity of Construction Materials for Mold Growth by Experimental Study

Abstract

Resistance of materials to mold fungi is directly related to the material properties and the environmental temperature and relative humidity level. Critical relative humidity occurs when the relative humidity reaches to the point where mold fungi can grow on the substrate. A strategy should be developed to address the conditions of mold fungi growth and use more suitable materials depending on the humidity conditions in the building. The purpose of this research was to establish the essential relative humidity of various construction materials based on their substrate category in order to get a better understanding of mold resistance and to reduce the danger of mold development. The critical relative humidity for six building materials was determined in this research to assess each substrate category’s resistance to mold growth. Inoculation of construction materials with six mold spores (Penicillium, Cladosporium, Chaetomium, Scopulariopsis, Aspergillus, and Acremonium) and incubation in a desiccator at 22° C (%75-95 ). For 3 months, samples were analyzed once a week. Mold growth was most sensitive to substrate category I (gypsum board) in this laboratory experiments. There was no evidence of growth in any of the glass or composite samples. The essential moisture level varied according to substrate category. For example, the essential humidity level for drywall (category I) was 80%, whereas for rock wool it was 85% (category II). At various relative humidity levels, the time needed for critical mold development varied. Critical mold development times for gypsum board are 12 weeks at 75% relative humidity and 1 week at 95% relative humidity. The greater the environment relative humidity, the less time essential mold development requires on the substrate.

Part of Mold & water-damaged buildings research · Curated by Lauren Lowenstein, The Biotoxin Lady