MOLD GROWTH ON WOOD UNDER FLUCTUATING HUMIDITY CONDITIONS

The growth of moulds and other discolouring fungi on sapwood of pine u nder fluctuating moisture conditions after inoculation with a conidial suspension, was studied. Experiments were performed in chambers in wh ich the relative humidity (RH) was controlled by salt solutions or gly cerol-water mixtures or in a humidity control chamber in which relativ e humidity was automatically controlled. The inoculated samples of woo d were subjected to varying intermittent moisture conditions with seve ral combinations of relative humidities from 35 to 100%. Growth halted during periods at RH below 80% but partly resumed after return to RH 97%. Growth rate was very slow when the fungi were subjected to rapid changes (6h/6h) in humidity between RH 97 and 75% or if the dry period was 1 week or longer. The fungi seemed to adjust to a high extent to moisture fluctuations according to a cycle with 24h at RH 97% alternat ing with 24h at RH 75%. The most Likely reason for the slow growth rat e at very rapid moisture changes is a slow increase of moisture at the surface of wood at these conditions. The results were analysed for th e effects of dry period durations and accumulated growth on wood in re lation to the sum of the periods at humidity levels earlier found to s upport growth under static conditions. The possible significance of th e results for development of mould problems in houses is briefly discu ssed.