Resistance of acetylated wood to biological degradation

Acetylated pine wood samples were tested in ground contact (stake test) at two test sites, one located in Simlangsdalen, Sweden, and one in Viikki, Finland, according to European standard EN 252. The test stakes were inspected annually and their condition was compared with that of untreated controls and of stakes treated with two reference CCA preservatives. The use of untreated controls and preservative treated wood gave a measure of the aggressiveness of the fungal decay at the individual test sites. The resistance to fungal decay of acetylated wood with an acetyl content of about 20% is of the same magnitude as for CCA treated wood at a high retention level (10.3 kg/m(3)). Exposure of acetylated mini stakes to three different unsterile soils in the laboratory showed that decay was significantly reduced at acetyl contents of 15.1%. An acetyl content of 18.5% prevented most attack by brown, white and soft rot fungi. Acetyl levels above 20.9% were required to eliminate attack by tunneling bacteria. Acetylated wood samples were also tested in seawater on the Swedish West Coast for their resistance to marine borers (EN 275). Results show that the acetylation of wood gives only minor protection against marine borers, although the degree of attack is lowered with increased acetyl content.