Topics
Insect Degradation
Fungi Degradation
Internal Growing Stresses
The rapidity and intensity of insect attack depend on the wood species as well as prevailing environmental conditions. Bark tissues usually plays a protective role, or at least retards attack, depending on texture, thickness and adherence to the underlying wood.
Certain types of fungi provoke changes which affect the physical or mechanical properties of wood, others course discolouration or stain. The staining fungi are usually confined to the sapwood, with the most common being blue stain fungi. Other stains (grey and brown) generally cause the wood to loose its sheen and lustre, thereby degrading its quality. Overseas test indicate that fungicide treatment of timber 24 hours after felling was to late to stop staining fungi. The hyphae had already penetrated the wood beyond the depth that the fungicide spray could reach. This shows how necessary it is to take immediate action against staining fungi. Contrary to what happens in insect attack infestation by fungi at first leaves no visible external marks so by the time signs appear on the surface of the log, fungicide treatment is entirely to late and is useless.
Wood rot fungi do not take hold of freshly cut timber as quickly as the staining fungi. Therefore logs which have been treated , transported and conditioned for veneer cutting on a normal schedule do not as a rule decay or rot.
The general rule is to reduce the time between felling and veneer manufacture to a minimum. A preservative must be applied as quickly as possible after felling, preferably within 24 hours, the preservative must be of the right type, not adulterated or diluted and its application must be thorough and cover all exposed areas. Preservatives for log protection should be a combination of fungicide and insecticide and should have residual, long term effectiveness.
The damage and degrade caused by splits and cracks due to release of internal growing stresses are due to rapid end drying, excessive exposure to the sun and elements, and mechanical damage in handling and transport. Resulting in losses in both quantity and quality of veneer, and provide ready access to wood staining or destroying fungi. Remedial measures consist mainly of observing normal precautions in felling, hauling and storing the logs, so as to keep the changes of such mechanical defects to a minimum. Painting or gang nailing the ends of the logs help minimise end checking.