The field tests included 11 different anti-sapstain preservatives and were carried out at different sawmills in southern Sweden. Drying conditions, climate and the local fungus flora were not identical for the different preservatives and comparisons between the preservatives should therefore be made with caution. Results obtained in the field tests are, however, in relatively good agreement with those found in the laboratory tests carried out with the pure preservatives. Especially Cuzol, a methylen-bis-thiocyanate/boric acid-product, showed a good effect against sapstain both in field and laboratory tests. However, Mykocid BS and Improsol 1 (two bifluoride products) as well as Mitrol 48 (benzalkonium chloride/guazatine) were also effective against sapstain. Hager Blue (boric acid/caprylic acid) was also fairly effective even if the untreated control material in this test was only moderately stained. Acceptable protection was obtained with the two Benomyl-containing preservatives and Thiobor (dimethyldithiocarbamate + borax). Mixtures of the various preservatives were tested in the laboratory as regards protective effect against sapstain, mould, thermotolerant mould and decay as well as chemical reactions that could be observed visually (precipitation, change in colour etc.). There was no absolute correlation between observed chemical reactions and changes in the biological effect. Mixtures resulting in reduced biological activity and which should be regarded less suitable are; Mykocid BS/ DuPont Benomyl, Cuzol/Thiobor, DuPont Benomyl/ Thiobor, Fennotox/Mitrol 48, Fennotox/Thiobor, Hager Blue/Sadolin Woodgard, Improsol 1/Mertect, Mitrol 48/Thiobor, Mitrol 48/Sadolin Woodgard and Mykocid BS/Thiobor. When mixing Hager Blue/Mykocid BS, Mitrol 48/Mykocid BS, Improsol 1/Cuzol and Mykocid BS/Cuzol precipitations occurred, which is a factor to be considered in practice since stirring may be necessary in the dipping tank. The preservatives based on bifluorides, Improsol 1 and Mykocid BS, penetrated about 1 cm into the wood after dipping and seasoning. A certain yellowish chemical staining was observed. Bifluorides are corrosive and attack steel and to a certain extent also concrete. Products containing boric acid and borates (Hager Blue, Thiobor, Benomyl + boric acid) also penetrated the timber to a certain extent. Thiobor reacted with certain parts of the heartwood which became slightly stained a reddish tone. The diffusion from the surface of the timber and inwards, which takes place when preservatives containing bifluorides, boric acid or borates are used, results in decreasing concentration of active components near the surface of the timber. This has to be considered when choosing the concentration of the treatment solution. Four of the preservatives included in the tests required stirring in the dipping tank. These are DuPont Benomyl 50, Sadolin Woodgard, Fennotox S2 and Mertect.

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