Comments on soft rot attack in timbers treated with CCA preservatives: A document for discussion

IRG/WP 1167

T Nilsson

This paper is not based on any particular results but rather on several observations of soft-rot during many years of studies, and on a review of the existing literature. The short time available has unfortunately not permitted a detailed review of the literature. Data and knowledge of important facts are lacking for several aspects of soft-rot attack and for reactions occurring in the wood as a result of the treatment with CCA preservatives. This has made several assumptions necessary and a number of suggestions are being made which are not backed up by results. But this document may nevertheless provide a basis for discussions. Hypothesis: (1) Soft rot attack in low susceptibility wood species is prevented at CCA levels which are too low for preventing growth of soft-rot fungi. (2) High susceptibility hardwood species are only temporarily protected by high retentions of CCA. The concentrations of CCA required are so high that they will be expected to considerably effect the grawth of soft-rot fungi. (3) Formation of T-branches is induced by a chemical factor, most probably of carbohydrate nature, in the wood cell walls. (4) The number of sites where this chemical factor occurs is depending on the carbohydrate/lignin ratio. Few sites occur in high lignin timbers whereas a high number of sites can be expected in low lignin timbers. (5) CCA treatment masks or modifies the sites so that the penetrating hyphae are unable to detect them. The masking is complete in timbers with a high lignin content whereby soft-rot attack is prevented. Only partial masking occurs in hardwoods with a low content of lignin which will allow soft-rot attack to occur. But the soft-rot decay rate is such hardwoods treated to high retentions of CCA will be reduced because of the toxic effects of the preservative.


Conference: 82-05-24/28 Çesme, Turkey

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