Decay and mold resistance of zinc borate (ZB) and calcium borate (CB) modified oriented strandboard (OSB) from southern mixed hardwoods and yellow pine was investigated in this study. Tests were done with brown rot, Gloeophyllum trabeum, and white-rot, Trametes versicolar, fungi for 8 and 12 weeks, respectively. Wood species and fungus type had significant influence on the decay resistance. Decay caused by brown rot was evident for all untreated southern pine and mixed hardwood OSB controls. White rot, however, did not cause significant sample weight loss for both species groups. The incorporation of ZB and CB into the OSB provides suitable protection against brown- and white-rot fungi. No significant weight loss was observed from the treated OSB. Microscopic analysis shows that the hyphae were abundant in wood rays and cell walls in the southern pine OSB controls attacked by G. trabeum. Untreated samples from mixed hardwoods and commercial OSB were most susceptible to mold growth. The borate-modified OSB from mixed hardwoods and southern pine effectively prevented the mold growth. Mold resistance was achieved with increase of borate retention level in the samples. Mixed hardwoods OSB showed a higher susceptibility to mold growth than southern pine OSB with or without borate treatment.

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