Characteristics of Mould Growth in Pine and Spruce Sapwood and Heartwood under Fluctuating Humidity

The importance of maintaining a healthy indoor climate has recently increased, as has the durability of building structures, and for this issue, we need to predict mould growth. To prepare this model under real conditions is challenging, and this work aimed to contribute data to this model. This article presents the findings of a laboratory study investigating the effects of fluctuations in the relative humidity and temperature conditions on mould growth on pine and spruce. The study compared the results to a previous steady-state experiment, demonstrating that fluctuations in relative humidity and temperature prolonged the onset of mould growth. The mould growth observed depended on the type of wood with pine or spruce wood exhibiting different growth patterns compared to heartwood or sapwood. In sapwood, mould growth was found to be almost independent of the direction of the fiber. The first microscopic indications of mould growth on pine sapwood were observed around day 76, with the first macroscopic indications observed around day 90. On the contrary, spruce sapwood demonstrated a limit for mould growth. The mould growth was only visible under the microscope with the first indications observed between the 72nd and 80th day. Furthermore, heartwood was found to be unsuitable for mould growth under fluctuating conditions.