Attempt for developing a new method for above ground field testing of wood durability
N Terziev, M-L Edlund
Field testing remains the most appropriate way for evaluation of wood preservatives or natural durability of wood species. Above ground tests are designed to answer specific questions concerning the outdoor utilisation of wood. Such methods supply additional information and confirm or reject preliminary laboratory results. The European standard (ENV 12037, "lap-joint") for assessment of the durability of preservative treated wood in above ground testing has recently been proposed. It may also be used to assess the natural durability of wood. The objective of the present paper is to bear some discussion on alternative above ground test methods. The existing lap-joint field test corresponds to the real exploitation conditions of timber, but shows no decay after 2-3 years of exposure. This could be misleading when assessing the efficiency of preservatives. The method suggested acts more quickly compared to the lap-joint method with regard to mould, stain and, presumably, decay fungi. It is an accelerated above ground field test providing conditions favourable for fungal growth, but following close the fluctuations of climate. Results are shown where samples treated with preservatives for above ground use and untreated samples were exposed to the accelerated above ground test for several months. Fungal discoloration of the timber surface was classified by visual examination according to a seven-grade scale. The field test described here may be recommended for quickly testing of the natural durability of wood in above ground conditions as well as for approval of preservatives.
Keywords: ACCELERATED FIELD TEST; ABOVE GROUND; MOULD; STAIN; SCOTS PINE; TEST METHOD