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All measures that are taken to ensure a long life
of wood fall under the definition wood preservation (timber
treatment). Apart from structural wood preservation measures,
there are a number of different (chemical) preservatives and
processes (also known as timber treatment or lumber treatment)
that can extend the life of wood, timber, wood structures or
engineered wood. These generally increase the durability and
resistance from being destroyed by insects or fungus. |
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Chemical
Preservatives
Timber or lumber that is treated with a preservative generally
have it applied through vacuum and\or pressure treatment.
The preservatives used to pressure-treat lumber are classified
as pesticides. Treating lumber provides long-term resistance
to organisms that cause deterioration. If it is applied correctly,
it extends the productive life of lumber by five to ten times.
If left untreated, wood that is exposed to moisture or soil
for sustained periods of time will become weakened by various
types of fungi, bacteria or insects.
Chemical preservatives can be classified into three broad
categories: Water-bourne salts, Oil-bourne preservatives,
and Light Organic Solvent Preservaives (LOSPs).Chromated copper
arsenate (CCA) Alkaline copper quaternary Other copper compounds
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Borate
preservatives
Borate treated wood is non-toxic to humans, and contains no
coppers or other heavy metals. Borate taken into the body
is excreted, rather than building up as heavy metals do. Unlike
most other preservatives, borate compounds do not become fixed
in the wood and can be washed out. Therefore they cannot be
used where they will be exposed to standing water. Recent
interest in low toxicity lumber for residential use, along
with new regulations restricing wood preservation agents,
has resulted in a resurgence of the use in borate treated
wood for floor beams and internal structural members. |
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Sodium
silicate-based preservatives
Sodium silicate is produced by fusing sodium with sand or heating
both ingredients under pressure. It has been in use since the
1800s. It can be a deterrent against insect attack and possesses
minor flame-resistant properties; however, it is easily washed
out of wood by moisture, forming a flake-like layer on top of
the wood. Other uses include fixing pigments in paintings and
cloth printing, and for preserving eggs. |
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Bifenthrin spray
preservatives
In Australia, a water-based bifenthrin preservative has been
developed to improve the insect resistance of timber. As this
preservative is applied by spray, it only penetrates the outer
2mm of the timber cross-section. Concerns have been raised as
to whether this thin-envelope system will provide protection
against insects in the longer term, particularly when exposed
to sunlight for extended periods. |
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Oil-borne
Preservatives
These include pentachlorophenol, copper naphthenate, and creosote.
All of them are toxic and are generally not used in consumer
products. |
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Coal-tar
Creosote
Creosote is a tar-based preservative that has been commonly
used for telephone poles and railroad ties. Creosote is one
of the oldest wood preservatives, and was originally derived
from a wood distillate. It often collects inside chimneys
causing a fire hazard. Creosote is regulated as a pesticide
and is not usually sold to the general public. It is still
used for railway sleepers and utility poles. |
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Linseed
Oil
In recent years in Australia and New Zealand, Linseed has
been used as a solvent to 'envelope treat' timber. This involves
just treating the outer 5mm of the cross-section of a timber
member with preservative, leaving the core-untreated. While
not as effective as CCA or LOSP methods, envelope treatments
are significantly cheaper as they use far less preservative.
Major preservative manufacturers add a blue dye to envelope
treatments. There is an on-going promotional campaign in Australia
for this type of treatment. Linseed oil is used to preserve
Wood fences, log cabins, and wood furniture.(Such woods as
Willow, Pine, oak and exc.) |
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Other Emulsions
Light Organic Solvent Preservatives (LOSP)
This class of timber treatments use white spirit as the solvent
carrier to deliver preservative compounds into timber. Synthetic
pyrethroids are used as an intecticide, such as permethrin,
bifenthrin or deltamethrin. In Australia and New Zealand, the
most common formulations use Permethrin as an insecticide, and
Propaconazole & Tebuconazole as fungicides. While still
using a chemical preservative, this formulation contains no
heavy-metal compounds. |
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Naturally rot-resistant
woods
This includes Western Redcedar, Huon Pine, Merbau, Ironbark,
many cypresses and Coast Redwood. These species are resistant
to decay in their natural state, due to high levels of organic
chemicals called "extractives", mainly polyphenols.
Extractives are chemicals that are deposited in the heartwood
of certain tree species as they convert sapwood to heartwood.
However, many of these species tend to be prohibitively expensive
for general construction applications. |
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