Mold and decay resistance of thermally modified douglas-fir heartwood

Abstract

Most thermal modification studies have attempted to improve the durability of sapwood; however, it may be more fruitful to improve the durability of heartwood that already has some inherent durability. The effects of pretreatments with boron or glycerol coupled with thermal modification on resistance to mold growth and fungal degradation were examined for Douglasfir (Pseudotsuga menziesii (Mirb.) Franco) heartwood, which is classified as moderately durable. Pretreatment with boron had marked effects on resistance to both mold and decay fungi, but the results were consistent with the well-known effects of this fungicide. Pretreatment with glycerol appeared to reduce mold resistance and had no effect on degradation by decay fungi. Thermal modification enhanced mold resistance with increasing temperature but had only a slight effect on decay resistance. These results suggest that thermal modification does not enhance performance to levels that meet North American durability requirements for aboveground, exterior exposures.