ABSTRACT
The effects of photochemical, chemical, thermal and mechanical action are usually of secondary importance in determining durability. The far higher durability of the heartwood of certain species compared with the sapwood is attributable primarily to the presence in the former of toxic substances, many of which are phenolic in origin. Durability of the heartwood varies considerably among different species, and is related to the type and quantity of extractives present; the heartwood of timbers devoid of extractives has a very low durability. The performance of materials in fire is an aspect of durability that has always attracted much attention, from the material user who has to conform with the legislation on safety and who is influenced by the weight of public opinion on the use of only ‘safe’ materials. Generally when the durability of timber is discussed reference is being made explicitly to the resistance of the timber to both fungal and insect attack; this resistance is termed natural durability.
