WHAT ARE THE LIMITING CONDITIONS FOR MOULD GROWTH (MINIMUM RELATIVE HUMIDITY, MINIMUM MOISTURE CONTENT, MIN/MAX TEMPERATURES)?
Relative humidity (RH), moisture content and temperature of the material are inextricably linked and are some of the most critical factors for mold growth or lack thereof, although substrate nature and mold species are also important. Most research has been done under steady state laboratory conditions where a material is in equilibrium with a constant atmosphere. Under these conditions, prolific mold growth does not occur when RH is maintained below 75-80%, as most fungi do not germinate and grow below this level. Small amounts of growth of some dry-loving fungi will occur on some susceptible materials below 80% RH, but growth is very slow. Generally, above 80% RH the rate of mold proliferation progressively increases. Some wet-loving molds, among which are several toxin producers (such as Stachybotrys) require the effective RH to be above 90% (described as a water activity aw of >0.90). Toxin production is increased at aw >0.95. Virtually no molds are able to grow below aw 0.65. In g
