Use of totally carbon-based preservatives to improve the performance of naturally durable woods

Abstract

Demand for naturally durable timbers has encouraged the development of more aggressively managed plantation of species such as teak (Tectona grandis) or California coast redwood (Sequioa sempervirens). A number of reports suggest that heartwood from some plantation-grown species tends to be less durable than that from naturally grown materials. Developing methods for improving the durability of these species will be important for maintaining their markets. One approach is to supplement the natural durability with colorless organic wood preservatives. In this report, the decay resistance of teak, redwood, and western red cedar sapwood and heartwood samples with and without supplemental treatment with didecyldimethylammonium chloride (DDAC) or 4,5-dichloro-2-N-octyl-4-isothiazolin-3-one (DCOI) was compared with samples treated with alkaline copper quaternary compound (ACQ) and untreated samples. All samples were exposed in a ground proximity test in Hawaii, and the degree of decay was visually assessed every 6 months over a 36-month period. The ACQ treatment generally provided the most protection, but its green color could negatively affect public acceptance of the materials. DDAC and DCOI both improved performance in most sapwood materials, but their effects on heartwood were less clear and a longer evaluation period will be required to determine the benefits of treating heartwood of these species.