Surface mould growth on wood: a comparison of laboratory screening tests and outdoor performance

Laboratory screening tests are commonly used to indicate wood materials’ resistance or susceptibility to surface mould growth, but the results can deviate from what happens during outdoor exposure. In this study, the aim was to investigate how well agar plate screening tests and water uptake tests can predict mould growth on exterior wooden claddings. The tested wood materials included Norway spruce heartwood (Picea abies), sapwood and heartwood of Scots pine (Pinus sylvestris), aspen (Populus tremula), acetylated Radiata pine (Pinus radiata) and DMDHEU-modified Scots pine sapwood. The agar plate test included four inoculation methods (two monoculture spore suspensions of Aureobasidium species, one mixed-culture spore suspension, and inoculation from outdoor air) and three incubation temperatures (5, 16 and 27 °C). Inoculation method and incubation temperature had significant effects on the mould rating in the agar plate screening test, but none of the agar plate test combinations gave good indications of outdoor performance. Results from the agar plate test gave significantly negative correlations or no significant correlation with results from the outdoor test. However, the water uptake test gave significantly positive correlations with outdoor mould rating, and could be a useful indicator of susceptibility of uncoated wooden claddings to surface mould growth.