FEATURES
Termites can cause devastating damage to timber .
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“ Durability of sapwood , irrespective of species , is low . It generally boasts a lower density than Heartwood and has a high moisture and starch content , all of which are conducive to fungal or insect degradation . Wood that is kept dry and is naturally durable is able to resist invasion by fungi or insects . Heartwood contains cells which have chemical deposits within the cells , little or no carbohydrates , and relatively lower moisture content . Heartwood in some species , such as sneezewood , can be highly durable while in others , for example pine or eucalyptus saligna / grandis , durability is low ,” explains Breedt .
He adds , “ Durability of permeable timbers may be increased by the addition of chemicals that are toxic to fungi or insects , or which reduce the possibility that the moisture content of wood will increase from the seasoned state . It is the addition of these chemicals that provides the basis of the timber preservation industry .
“ Permeability , the ability to penetrate wood with chemicals resistant to insects or fungi , is largely dependent on being able to remove moisture so that the preservative liquid can be added in its place . Most preservatives require pressure to push them deep into the wood . The depth to which penetration is achieved is dependent on the available Sapwood , density , chemical inclusions within cells , moisture content , cell type , techniques used and so forth . Generally , softwoods are more easily penetrated than hardwoods , and sapwood is more easily penetrated than heartwood .”
PROTECTING YOUR TIMBER
Depending on the service and exposure conditions , timber can be attacked , degraded and even completely destroyed by one or more wood deterioration factors . Proper design and preservation practice can eliminate or minimise such an attack , which include fungi , wood destroying insects , weathering and fire .
According to TimberLife director Willie Conradie , the development of fungal attack , under favourable conditions , can be rapid . “ Wood degrading fungi can be broadly divided into two main groups : wood discolouring fungi ( mould and sapstain fungi ) and wood rotting fungi ( brown rot , white rot and soft rot fungi ). Although wood discolouring fungi does not damage the wood structure , they adversely affect the general appearance of the timber ,” explains Conradie .
He adds , “ Mould fungi produce masses of pigmented spores , usually greenish or black , that cause superficial discolouration of the wood surface . Sapstain fungi on the other hand cause deep and permanent discolouration of the wood . Wood rotting fungi attack the wood itself and can weaken the wood structure to such an extent that it breaks and crumbles away .”
See more on page 32
30 AUGUST / SEPTEMBER 2018 //