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Using softwoods for decks
Whilst hardwood is generally the preferred lumber
species for exterior decking due to its hardness,
resistance to wear and attractive colour, softwood
species are commonly used, particularly where cost is an
important factor. But the drawback of most softwoods is
that they are not naturally durable so are unsuitable
for use in areas fully exposed to the weather unless the
wood is properly treated with a recognized wood
preservative or completely sealed with an impervious
surface coating. So when selecting a softwood species,
one of the most important considerations is that these
species used should be either a recognised naturally
durable species such as Western Red Cedar, some species
of cypress, larch or pine, or that it has been treated
with an appropriate and good quality preservative.
For more than 70 years, the most commonly accepted
wood preservative treatment chemical has been CCA
(copper chrome arsenic), which gained popularity due to
its effectiveness and relatively low cost. (CCA treated
lumber can normally be distinguished by the greenish
tone it imparts to the wood). However in recent years,
many national organisations and authorities have
announced either bans or restrictions on the use of
lumber treated with CCA. For example, in Australia from
March 2006, CCA treated timber will no longer be
permitted for use as handrails, decking boards, picnic
tables, or children's playground equipment in new
installations. And in Japan, CCA treated lumber is
generally not permitted any longer for public use in
major cities for municipal projects.
Although there is apparently no firm scientific proof
to support the contention that CCA timber is harmful to
health provided it is handled correctly, such cautions
or bans have been instituted as a precautionary measure.
Nevertheless it is always best to err on the side of
safety, so it is recommended that when working with CCA
treated lumber, to apply protective clothing including
goggles, face mask and gloves. CCA treated lumber also
should never be burnt in an open fire but must be
disposed of according to local regulations.
Fortunately a number of alternative wood treatment
products to replace CCA are now available, the most
common of which is probably ACQ (alkaline, copper,
quaternary). Such products use low toxicity, active
ingredients such as recycled copper and modern organic
biocides to give the lumber the required long-term
protection against wood destroying fungi, termites and
other wood eating insects. Although such products have
not been available for a sufficiently long time for
extensive natural durability data to be collected, most
manufacturers will provide at least 25 years guarantee
on the life of treated lumber.
So if you wish to use a softwood species for your
deck, check what preservative treatments have been
applied, and especially with the newer preservative
treatment chemicals, ask what guarantee the lumber
supplier is prepared to offer on the lifetime of the
decking material. Although untreated softwoods typically
have a very short life in exterior exposed conditions,
if pressure treated with appropriate chemical, a
softwood deck will provide many years of continual use
and enjoyment.
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