Unprotected wood outdoors is exposed to a number of biotic and abiotic factors of decomposition. In this study we observed the occurrence of mold and staining-fungi on unprotected wood specimens of spruce (Picea abies), Scots pine (Pinus sylvestris) heartwood and sapwood and European larch (Larix decidua) heartwood, which were exposed in the laboratory and outdoors. The purpose of the research was to determine the resistance of individual types of wood on fungal staining. Monitoring of wood moisture content (MC) in the laboratory showed that relative humidity (RH) of 87 % and 100 % resulted in the highest MC of Scots pine, heartwood and sapwood, but outdoors, where were the samples were exposed also to rain, Scots pine sapwood reached the highest MC, and Scots pine heartwood the lowest one. The colour of the wood in the climate with higher humidity has changed the most on spruce wood and sapwood of Scots pine, and the least on European larch heartwood. The specimens in the field test showed the largest colour changes on sapwood of Scots pine and the smallest on the European larch. In the assessment of colour change by fungi, which we determined with two methods (SIST EN 152-1 and Pernilla Johansson), we came to comparable conclusions, regardless of the method used. RH of 87% caused the highest staining rate on European larch, but at RH of 100 % on the sapwood of Scots pine and spruce. The lowest staining rates were determined on Scots pine heartwood, regardless of the RH. Outdoor exposure caused the most staining on Scots pine sapwood and the least on the heartwood of Scots pine, which was in accordance with our hypothesis, which proved that is heartwood of Scots pine is more resistant and aesthetically pleasing for outdoor use than European larch.
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