Standard Test Methods for Wood Preservatives by Laboratory Agar-Block Test

IRG/WP 06-20350

P K Sarker, M A Rahman, M R Bulbul, T Das, G N M Ilias

Wood is one of the most valuable and versatile resources for all sorts of constructional purposes. But timber in its various forms is subjected to several types of deterioration. This standard lays down the method for the laboratory determination of threshold value of wood preservatives against fungi. Most chemicals are initially tested for their ability to control decay fungi in agar-block tests. In an agar-block test, blocks of wood containing a pre-determined retention level of chemical are exposed to wood-destroying species of both brown-rot and white-rot fungi. The blocks along with the fungi inoculums are placed within a sealed dish containing agar. Efficacy is measured as a loss of block weight. The test fungus to a medium containing known concentrations of the test chemical, or soaking filter paper in the test chemical and placing this on the surface of a previously inoculated plate. The presence of the fungus and its growth rate are used as a measure of chemical effectiveness. These results are then compared with results of similar tests on accepted preservatives. Whereas this method provides a relative measure of toxicity, the growth of fungi on artificial media is markedly different from growth in wood. This test method varies widely between laboratories. The efficacy of wood preservatives provide valid data, the time required to obtain definitive results is too long because reliable decisions on efficacy against wood decay organisms must rely on long-term field test data. This goal will not be realized until we develop a better understanding of the many variables that influence microbial decay rates, develop improved methods for detecting and quantifying the extent of wood decay and couple these developments with improved designs for test specimens and methods. The main objection to the malt-agar toxicity test is that the substrate is not wood. But this testing method takes minimum time among other methods which is save the time, money and labor of the users.

Keywords: wood preservatives, testing, agar-block

Conference: 06-06-18/22 Tromsoe, Norway

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