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Timbers
are usually classified as non-durable or durable depending
on whether their heartwood is liable to be attacked by fungi
and insects or not. In some countries the durable woods are
further divided into three groups as (1) highly durable (2)
moderately durable and (3) less durable depending upon the
degree of damage of a standard sized piece of wood on exposure
directly to wood destroying agencies. Similarly the various
species of wood are classified as easily treatable or not,
depending upon the capacity of the species to take chemicals
for preventing attack by fungi and insects. At present there
are no adequate laboratory or field data on rubberwood to
classify its durability or treatability, but there are various
industrial and field experiences, from which it is known that
rubberwood is definitely non-durable, but fairly easily treatable
by water soluble chemicals or even oil type preservatives.
Several agents damage rubberwood including fungi and insects
which require to be treated chemically. There are several
types of fungi which are known to attack rubber wood. Some
of the well known among them are Lenzites palisotti, Ganoderma
applanatum, Tramates corrugata, Pollyporous zonzlis, Lentinus
blapharods and Schizophyllum commune. Similarly some of
the insects found to attack rubber wood are those belonging
to families Cerambycidae, Bostrychidae, Lyctidae and Platypodidae.
To protect wood from the attack of these agents, it has
to be treated with chemical preservatives. The common types
of preservatives are oil-based and water-based. In the oil
based preservative, coal tar creosote, with or without admixture
of fuel oil, is used mostly for exterior use of rubber wood.
The discolouration and unpleasant odour restricts its use
at many places. However this is toxic to many types of organisms
and also prevents any further splitting in wood. Water based
preservatives contain toxic inorganic salts dissolved/dispersed
in water. The leachable types amongst these are zinc chloride,
boric acid or borax and sodium pentachlorophenate. Non -leachable
water based preservatives include copper-chrome-arsenic
(CCA), acid-cupric-chromate (ACC)
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