The aim of this investigation was to determine the effect of 5, 10, 15 and 20 percent acetylation weight gains on the susceptibility of Pinus radiata sapwood to mould and stain fungi, and to establish if an acrylic paint, an oil-based stain and a water repellant gave superior protection from fungal growth on wood treated to 20% acetylation weight gain, compared to untreated wood. One treatment set was tested using a modified anti-sapstain screening trial method, designed to give optimal conditions of relative humidity (>95%) and temperature (25°C) for mould growth. A second treatment set was exposed to the weather and assessed at 10, 21 and 40 weeks. The results showed that over the three week laboratory trial period, the rate of colonisation by mould fungi of Pinus radiata sapwood treated to 20% acetylation weight gain was significantly (P < 0.001) slower than on untreated wood. This was attributed to the lower availability of readily assimilated nutrients such as sugars and starch in acetylated wood. The rate of colonisation by mould fungi of acrylic-finished sapwood treated to 20% acetylation weight gain was significantly slower than on acrylic-finished untreated wood. Acetylation up to 20% weight gain conferred no protection from mould growth for test samples exposed to the weather. None of the finishes perfomed better on acetylated wood than non-acetylated wood when exposed to the weather.

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