Treated Wood
When you want to use wood that is not naturally decay resistant in a wet
application (outdoors, for example) or where it may be at risk for insect attack, you need to specify preservative-treated
wood. This is lumber that has been chemically treated to make it unattractive to fungi and other pests. In the same way that
you would specify galvanized steel where it would be at risk of rusting, you specify treated wood where it will be used in
a setting conducive to decay.
Wood does
not deteriorate just because it gets wet. When wood breaks down, it is because an organism is eating it as food. Preservatives
work by making the food source inedible to these organisms.
Properly preservative-treated wood can have 5 to 10 times the service life of untreated wood. This extension
of life saves the equivalent of 12.5% of Canada's annual log harvest.
There are two basic methods of treating: with and without pressure. Non-pressure methods are the application
of preservative by brushing, spraying or dipping the piece to be treated. These are superficial treatments that do not result
in deep penetration or large absorption of preservative.
Deeper, more thorough penetration is achieved by driving the preservative into the wood cells with pressure.
Various combinations of pressure and vacuum are used to force adequate levels of chemical into the wood. Pressure-treating
preservatives consist of chemicals carried in a solvent. The solvent, or carrier, is either water or oil. Waterborne preservatives
have become increasingly popular over the last 20 years, due to the absence of odor, the cleaner wood surface and the ability
to paint or stain the wood product.
The
most commonly used wood preservatives in North America are amine copper quat (ACQ) and copper Azole (CA). These preservatives
are all applied with pressure. They have a green tone, which fades over time.
Borates are another class of waterborne
preservative gaining in popularity. Borates are colorless, non-toxic to humans, and can be applied to wood with or without
pressure. Their use is currently limited to applications which are protected from rain and other persistent sources of water.
These include framing in termite areas and repair of decayed framing in leaky buildings where the main moisture source has
been eliminated.
While wood has been
used in construction for hundreds of years, today's homeowners have a heightened awareness about the potential dangers
of mold / fungus growth in their home. New treatment methods are now available to protect the structure from mold damage before,
during and after construction. Some of these treatments are sprayed on the job site, while others are factory pre-treatment
methods.
