The present study was initiated as a consequence of restrictions against the use of CCA-type wood preservatives in Sweden in the 1990s. New copper-based formulations were introduced on the market and to some extent, also alternatives to preservative-treated wood, such as thermally and chemically modified and linseed oil treated wood as well as heartwood of non-tropical naturally durable wood species like oak, pine and larch. For most of the alternatives to CCA, no or very limited documentation on durability properties was available at that point. Field trials in and above ground were therefore started at test sites in Sweden and Hawaii, USA. Results after 11 years’ testing in Sweden and 9 years in Hawaii are presented, and the main conclusions are: • All the natural durable species tested were severely attacked by decay after 11 years exposure in Sweden, both in and above ground, and after 9 years above ground exposure in Hawaii • For the “alternative treatments” acetylation performed best, both in and above ground and is the only treatment, preservative treated wood included, that obtained a durability comparable with CCA-A. • Thermally modified wood had initially no visible sign of decay, but lost a good deal of its strength during treatment. After prolonged exposure, however, both in ground and close to ground the fungal degradation increased and after 11 years it is severely attacked. • A low level of linseed-oil treatment gave almost no protection. Linseed oil-treated wood with a high retention of linseed oil performed well, but because of the poor appearance the use in practice seems limited. • Wood treated to Use Class 3 according to EN 335-1 is not recommended for use in ground and consequently, most of them performed well above ground, less good in ground but better than the naturally durable wood. Of the chromium and arsenic free preservatives Impralit KDS was the least successful, much likely due to its comparatively lower copper content. • The different test methods gave the same order of ranking of the three groups of materials tested, although the rate of degradation differed.

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