Preserving treated wood is a very different process, using different preservatives than it was. But it is fair to say that there still remains a good few mis-conceptions about preservatives used in treating wood today in this 21st century.
The Wood Preservers Institute (wwpinstitute.org) on www.buildings-products.com – highlighted in a recent TTF Blog post – that the ‘what’s in wood’ enquiry is a question that comes up quite regularly in the lumber and plywood aisles of Timber Yards and DIY shops in many different locations.
So, as a starter, a key but fair question might be – ‘What exactly is the reason today why we pressure-treat wood products as we do ?”
The Wood Preservers Institute sets the scene on this key question, “Wood is, of course, a natural material and has unique qualities that make it an excellent building material. But Mother Nature can be a cruel mistress, seeking to decompose organic materials and return them to the Earth to support new growth.
Decay fungi and insects are part of the cycle of breaking down wood fibre once it’s no longer part of a living tree. While that may be great for nature, you don’t want that to happen to wood that is a structural element in your home or outdoor living area.
The most effective protection for wood is to infuse it with preservatives and keep fungi and insects from eating it. Pressure treating the wood extends the service life from a few years to decades, helping ensure sustainable forests”.
One common misconception, say the Institute, is that preservatives are poison. In reality, preservatives prevent fungi or insects from degrading the wood by creating a long-lasting disinfectant barrier.
Copper serves as the chief ingredient. Today’s preservatives contain as much as 50% to 97% soluble or ‘micro-nized’ copper. Most decay fungi, termites and other organisms don’t eat wood containing copper. While copper is effective, some organisms are tolerant to the element. Mixed with the copper are bio-cides and fungicides to enhance the protection. All of these are suspended in water, which carries preservatives into the wood when pressure is applied.
Two types of bio-cides are commonly used in preservatives: azoles and quaternary compounds. These chemicals aren’t used exclusively for wood preservatives, they are in fact also found in a host of consumer products.
These bio-cides and others, such as DCOI, are effective in protecting wood on their own. Carbon-based wood preservatives, such as PTI and EL2, contain no copper and rely on the protective characteristics of the bio-cides.
In the Mix
These compounds aren’t simply mixed together and sold as treatments.
Preservative manufacturers thoroughly research, test and monitor the formulations to ensure effectiveness when infused into wood. Each preservative must be approved by the U.S. Environmental Protection Agency (EPA), which requires extensive toxicological reviews to determine any potential human health or environmental risk.
National consensus standards, administered by the American Wood Protection Association, determine the amount of preservative required in the wood to protect it for its intended end use.
This process helps promote the safety of preserved wood by providing a balance between protecting the wood and minimizing the amount of preservative that may move into the environment.
So – a key question is then – “how much preservative is in the wood?”
In most cases, it is less than 1% of the weight of the wood. Preservative treating also enhances the sustainability of wood. Over the decades the wood can remain in service, a new tree can be grown to replace it in the future. Compared to alternative materials, life cycle science shows preserved wood has far fewer impacts on the environment.
When taken together, preserved wood products are indeed safe. Of course, use common-sense precautions when handling preserved wood.
The requirements are the same for both preserved wood and untreated wood – wear gloves and long-sleeved shirts, and avoid inhaling sawdust by wearing a dust mask when cutting or drilling.
The Institute confidently sums up – “Preserved wood today is a safe, reliable and environmentally responsible building product that can provide decades of protection and enjoyment.” – So now you know!