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Leaching of boron wood preservatives - a reappraisal
By J D Lloyd, September 1995.
Download Lloyd-_Leaching_of_boron_wood_preservatives (pdf)
Executive summary
Boron compounds in current use as wood preservatives are susceptible to loss via leaching, under certain conditions. This is because they are not chemically fixed after treatment and remain mobile within the treated wood. Available data on this phenomenon, gathered over fourty years, has been reviewed in this paper. It would appear that the significance of this problem has been over-stated for many years.
From the data reviewed it can be concluded that there is no danger of efficacy loss due to external exposure during construction and in fact boron can continue to provide good protection of timber in most practical exposed non-ground contact situations. Loss of these preservatives can only take place to a serious degree when treated timber remains wet throughout its cross section for long periods while at the same time having an external sink for boron migration. Sample size, test methodology, initial over-treatment and sample drying during test, can all be important factors when considering boron loss.
With the advent of suitable standard test methodology and the development of new formulation technology, it will be possible to expand the current use of boron based preservatives. This has already become evident with the increased reliance on boron in many of the recently developed 'fixed' preservative systems designed for exterior and ground contact applications.
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