The influence of natural durability of four different Larix species to their possible end-use in construction industry

Importers of Siberian Larch claimed to have a material, which can replace pressure, treated wood in soil contact. This gave reason to investigate the durability of 4 different Larix species (L. decidua, L. sibirica, L. decidua x sibirica, L. gmelini var ologenis) coming from 7 different origins in comparison with sapwood of Pinus sylvestris untreated as well as pressure impregnated with retention of 2 and 9 kg CCA per m(3). 10 mini stakes of each material in the size of 200 x 20 x 8 mm were installed in 1997 in the soil of the BFH test site (altitude = 24 m above see level, latitude = 53.5028 North, longitude 10.1982 East). Within the first 2 years all except one untreated specimen of the Scots pine sapwood had failed. Within the first 3 years all except one of the Scots pine with a retention of 2 kg of CCA had failed. Within 5 years all specimen of Larix sp., independent from the species, had failed, whereas the pressure impregnated Scots pine with a retention of 9 kg CCA /m(3) was either not or only slightly attacked. Mean life time and the average life time - which were about the same - served to classify the natural durability of the tested materials according to EN 350-1 (1994). All tested material was in the range of the value given in EN 350-2 (1994): "moderately to little durable" (European durability class 3-4). This was also valid for Siberian larch with narrow grow rings. From this results can be concluded that the performance of Larix heartwood in ground contact is far below that of wood properly treated with 9 kg CCA /m(3). The field results are compared with earlier lab results using the same source of Larix material (IRG/WP 97-10228; IRG/WP 98-10287; IRG/WP 0010350).