Boron treatment was approved for exterior, above ground use in New Zealand in 1958, provide treated commodities were painted with a three-coat paint system. Above ground tests of rail units and L-joints were established at the NZ Forest Research Institute (now Scion) between 1967 and 1980 to monitor performance of boron treatment in relation to that of untreated and CCA-treated timber. Results showed that even without any maintenance of the paint coats, boron treatment to retentions currently used at the time test were established considerably extended service life compared with that of untreated test units. After 35 years' exposure, painted boron treated rail units had a greater Index of Condition than unpainted CCA-treated units. Losses of boron from leaching were substantial in all tests, but this was highly likely to have been the result of lack of maintenance of the paint coats.

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