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| Wood
Preservatives
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A great deal of research has been done on wood preservatives over the years.
Here are some of the compounds that have been studied.
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Borates |
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Currently, zinc borate is
available in some composite products, and disodium octaborate tetrahydrate
(DOT) is popular for pretreatment of construction wood. With pressure
treatment, borates can penetrate refractory wood species like Douglas-fir
very well, which is an advantage over some other wood treatments. DOT
solutions are also sometimes applied to the wood surface for remedial
termite control, but these remedial treatments do not penetrate as deeply
as pressure treatment or dip-diffusion.
Laboratory and field tests of
borate-treated wood and composites have demonstrated the effectiveness of
borates against termite attack. However, it is important to have the right
concentration of borate in the wood to protect it against a particular
termite species, and to not leave unpainted treated wood exposed to
running water. |
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CCA |
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CCA (chromated copper arsenate) is a popular
preservative which is quite effective against termites and decay at
relatively low retentions, so long as the wood is thoroughly penetrated by
pressure treatment. However, refractory wood species like Hawaii's
perennial favorite, Douglas-fir, do not attain the same degree of
penetration beneath the surface as other more easily treated woods, such
as pine.
Although it has been shown that even
relatively low retentions of CCA are quite effective, it has been
suggested that more thorough penetration of CCA would be necessary for
longer-term exposure of refractory woods. |
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Copper naphthenate |
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Copper naphthenate (abbreviated
Cu-Naph) is a fungicidal wood preservative that has drawn intrest
as a treatment for utility poles. Until recently, information on termite
resistance of wood pressure-treated with copper naphthenate has been
somewhat scarce.
Results of our laboratory study of copper
naphthenate suggest that even under high weathering conditions,
substantial amounts of preservative can be expected to remain in wood
treated to target retentions of 0.150 pcf (pounds per cubic foot).
Weathered wood samples treated with this retention of copper naphthenate
sustained less than 4% mass loss after laboratory exposure to Formosan
subterranean termites. These findings indicate promise for copper
naphthenate applications, so long as the retention is sufficiently high.
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ACZA |
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ACZA (ammoniacal copper zinc
arsenate) is an arsenical, ammoniacal wood preservative which tends to achieve better
penetration in difficult to treat (refractory) woods such as Douglas-fir. This penetration is
aided by the practice of incising the wood. ACZA is not as popular in
construction as some of the other wood preservatives due to its cosmetic
appearance (incising marks and dark color).
Laboratory and field studies support the
use of ACZA as a protective treatment against termite attack, even in
refractory wood species, despite its relative lack of popularity for
construction purposes.
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Chlorthalonil |
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Chlorothalonil (tetrachloroisophthalonitrile,
or CTL), is a versatile fungicide which is widely used in
agriculture in the U.S. It is used as an
anti-fungal agent in some wood coatings, and is under development for
use with oil solvents as a preservative.
A Laboratory study involving different
retentions and solvents indicates that CTL will discourage Formosan
subterranean termites from feeding at appropriate retentions. Although it
is not commercially available, research continues with CTL in an effort to
narrow down threshold retentions and to assess the value of combining CTL
with other preservative components, like insecticides.
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