Durability
Durability refers to the natural durability of the
heartwood of the timber. It has been found useful and
convenient to classify durability into four groups, as shown
in the table below.
Natural Durability Grouping
Group Number of years
Very durable exceeding 10 years
Durable 5 - 10 years
Moderately durable 2 - 5 years
Non-durable 0 - 2 year
The placement of any timber in any of these four groups is
based on its performance in 'graveyard' testing. This method
of testing entails the monitoring of test-sticks measuring 50
x 50 x 600 mm buried in test grounds. The number of years that
the test-sticks can last is the basis for the grouping.
Great care should be exercised when considering durability.
It must be emphasised that the number of years, shown in the
Table above, is relevant only to the test-sticks, which
measure only 50 x 50 mm in cross-section, and that the tests
have been conducted under extremely drastic environmental
conditions where the test-sticks are subjected not only to
weather extremities but also to attack by a very wide range of
woodattacking organisms.
The number of years shown above is therefore only a
yardstick for the grouping exercise and the actual service
life of the timber can be expected to be much better under the
more docile conditions for common usage, especially in
temperate countries where climatic and other conditions are
less conducive to the activity of biodeteriorating organisms.
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