LABORATORY EVALUATIONS OF WOOD PRESERVATIVES .3. EFFECTIVENESS OF AUSTRALIAN VERTICAL RETORT CREOSOTES AGAINST DECAY IN RELATION TO PHENOLIC CONTENT

Twelve creosotes were tested in Pinus radiata sapwood against Lentinus lepideus using a modification of the American ASTM D 1413–61 method of creosote evaluation by soil-block decay test following accelerated laboratory weathering. Losses of creosote during laboratory weathering were inversely proportional to the logarithm of the initial retention; for an initial retention of 6 lb/cu ft, they varied from 48 to 77% and were closely correlated with the proportion of creosote distilling below 315°C. Threshold retentions ranged from 3.1 to 14.4 lb/cu ft (50 to 231 kg/m3) and were inversely related to initial phenolic content, which varied from 27.6 to less than 6 ml/r00 g. Threshold retentions were also influenced by resistance of the creosote to laboratory weathering and were found to be closely related to, and possibly predictable from, a “residual phenolic value” (initial phenolic content X proportion of creosote remaining after distillation to 230°C). The relationship between threshold retentions and triethylene glycol (TEG)-insolubles was also investigated. The importance of the phenolic content was confirmed for one creosote by testing the phenolic fraction and the rest of the creosote separately. The phenolic fraction was much more toxic than the phenol-free fraction to L. lepideus, Lenzites trabea and Pycnoporus coccineus and made a greater contribution than the phenol-free fraction to the preservative performance of the creosote for the two brown rot fungi but not for P. coccineus. This work has resulted in an increase in the required phenol content in the Australian Standard Specification for creosote from 5 to 16%. Criticisms are made of the ASTM method as regards variation in temperature within and among blocks during the weathering procedure and as regards difficulties in objective computation of threshold retentions. Threshold retentions for Lentinus lepideus were obtained by using a linear relationship found between logarithm of creosote retention and logarithm of weight loss due to decay. © 1969, IEEE. All rights reserved.