Treating Timber
Find Out Why and How Timber is Treated.
Treating timber is essential to extend its lifespan, allowing it to withstand environmental elements, decay, and insect damage. By doing so, we not only protect our wood products but also contribute to the conservation of our forest resources by reducing the need for frequent harvesting.
Properly treated timber can be used in a range of building situations and environments and can last for decades, even in challenging conditions.
Why Treat Timber?
Timber is a versatile and sustainable building material, but not all species are equally durable. While some timber species naturally resist insect attacks and decay, Pinus Radiata, the most commonly used timber in New Zealand and widely in Australia, lacks this natural durability. This makes it essential to treat Radiata Pine to meet Building Code requirements and consumer expectations, ensuring it lasts as long as it should in various applications.
Pinus Radiata: The Ideal Candidate for Treatment
Pinus Radiata is highly receptive to treatment due to its unique cell structure, making it the most easily treatable timber species globally.
When properly treated, Pinus Radiata can meet the durability standards required by building legislation in both New Zealand and Australia, offering reliable performance in a wide range of building applications.
Properly treated timber remains strong, resistant to decay, and protected against insects, making it a dependable choice for long-term structural integrity in a wide range of applications.
Understanding Treatment Standards
In New Zealand, the Building Code NZS 3640:2003 and AS/NZS 1604 serve as the foundational standards for the treatment of timber, ensuring it meets the durability and safety requirements necessary for use in construction.
These codes outline the specific processes and criteria that timber must undergo to be deemed suitable for various building applications. They provide detailed guidelines on how preservatives should penetrate and be retained within the timber, ensuring it can withstand the environmental conditions to which it will be exposed.
In addition to NZS 3640:2003, other related standards, such as those found in AS/NZS 1604, apply to reconstituted wood products like particle board, plywood, laminated veneer lumber, and glue-laminated timber. These standards are crucial in determining how these materials should be treated to ensure they meet the required durability standards.
Understanding Hazard Classes
A key aspect of determining the treatment standard that wood needs is the concept of Hazard classes. Hazard classes categorise the environmental risks that treated timber might face, such as exposure to moisture, insects, or decay.
Hazard classes range from low-risk indoor environments to high-risk outdoor or ground-contact situations. The higher the hazard class, the more stringent the treatment requirements become. This ensures that timber used in high-risk environments, such as those exposed to constant moisture or in direct contact with soil, receives a higher level of preservative treatment to protect it from decay, insect attack, and other forms of deterioration.
Want to know what hazard class timber you need? Check out our handy hazard class guide.
By treating timber according to the standards governed by the Building Code and guided by the appropriate hazard class, it can be confidently used in a wide range of construction applications. This approach not only ensures long-term durability and performance but also guarantees full compliance with New Zealand’s building regulations, offering peace of mind to both builders and homeowners alike.
Treatment plants that meet these stringent standards are licensed to use the WOODmark®, a mark of quality that signifies the timber has been treated to the highest industry standards, ensuring its reliability and excellence in any application.
Types of Timber Treatment
CCA Treatment
CCA treated timber is wood that has been pressure-treated with a preservative containing copper, chromium, and arsenic (CCA) to resist decay and insect attack.
CCA treated timber is ideal for outdoor structural and decorative uses, such as fences, decks, and playgrounds.
LOSP Treatment
LOSP timber treatment is a process that uses a white spirits-based or water based preservative, applied through a controlled vacuum process, to protect wood without altering its dimensions.
LOSP treated timber is commonly used for high-value building components like fascia, weatherboards, door and window joinery, and panelling.
BORON Treatment
Boron treated timber is treated with boron-based preservatives to protect against insects and decay. This treatment penetrates deeply into the wood, offering effective protection while being safe for indoor use.
Ideal for framing, flooring, and other interior structures. It is the most common form of treatment used for structural timber used within a building envelope.
Timber Treatment Processes
There are a range of different techniques for treating timber. The specific method of treatment varies depending on the type of preservative being used, each tailored to achieve the best possible protection for the timber. Each of these treatment processes is carefully designed to ensure the timber meets the required standards for durability and performance, providing long-lasting protection for various building and structural applications.
Pressure Treatments
These are typically used for water-based preservatives such as CCA (Copper Chrome Arsenate), ACQ (Alkaline Copper Quaternary), and Copper Azole.
Pressure treatments involve forcing the preservative deep into the wood under high pressure, ensuring thorough penetration and long-lasting protection against decay and pests.
Low-Pressure Treatments
Solvent-based preservatives, including Propiconazole + Tebuconazole, and Copper Naphthenate are applied using low-pressure processes.
These methods are also used for boron formulations, allowing the preservative to permeate the wood without excessive force, making them suitable for specific applications where less invasive treatment is necessary.
Spray or Dip Processes
These processes are commonly employed for certain boron formulations and traditional boric diffusion treatments.
The timber is either sprayed with or dipped into the preservative solution, allowing the chemical to coat and penetrate the wood surface.
These methods are typically used for lighter treatments where deep penetration is not as critical.
Testing Treatment Quality
Treatment plants that treat wood in accordance with the Building Code and hold WOODmark® licenses must adhere to strict standards to ensure the quality and safety of their products. The WOODmark® programme mandates that licensed treatment plants conduct regular internal testing of their timber at intervals specified in the Timber Preservation Quality Manual.
In addition to these internal tests, WOODmark® auditors carry out independent testing of the production process four times a year. This typically involves spot testing using reagents, with samples sent to accredited laboratories for more detailed analysis. These rigorous testing procedures ensure that all treated timber meets the highest industry standards for durability, safety, and performance.
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