Understanding Timber Preservative Codes
When selecting treated timber for your home or building project, it’s important to ensure that the wood you’re using has been treated with the appropriate preservatives.
The Right Timber Preservative for the Job
When choosing treated timber for your home or building project, it’s crucial to make sure that the wood has been treated with the correct preservatives.
These preservatives safeguard the timber from decay, insects, and other damaging elements, ensuring it remains durable for many years. In New Zealand, timber treatment is governed by the NZS 3640:2003 and AS/NZS 1604 standards, which outlines the approved preservatives and their specific uses.
What Are Timber Preservatives?
Timber preservatives are chemicals that are applied to wood to protect it from pests, fungi, and weathering. These preservatives are carried into the wood using either water or white spirits, allowing deep penetration to protect the timber effectively. Each preservative is suited to different conditions and uses, so it's crucial to choose the right one for your project.
Decoding Timber Preservative Numbers
Each approved timber preservative in New Zealand is assigned a unique code number, which is branded onto the treated wood. These numbers help you identify the specific treatment used, ensuring that the timber meets the required standards for its intended use.
Here’s a breakdown of the most common preservative numbers you might encounter:
01 - CCA Oxide
A widely used preservative, Chromated Copper Arsenate (CCA) Oxide is effective against decay and insects, making it suitable for outdoor and structural uses.
02 - CCA Salt
Similar to CCA Oxide, this preservative also protects against decay and insect damage but is formulated slightly differently for particular applications.
11 - Boron
Often used in interior timber, Boron is effective against termites and fungal decay but is less suitable for outdoor use unless it’s sealed or protected.
56 - TBTO
Tributyl tin oxide (TBTO) is a preservative that offers protection against marine borers and fungi, making it ideal for timber used in marine environments.
57 - Copper Naphthenate
Known for its distinctive greenish tint, this preservative is effective against decay and insects and is commonly used for utility poles and fence posts.
58 - Copper Azole
A newer generation preservative, Copper Azole provides protection against decay and insects and is suitable for a wide range of outdoor applications.
62 - TBTN
This preservative, also known as Tributyl tin naphthenate, is particularly effective against marine borers, making it ideal for use in timber exposed to seawater.
63 - IPBC
Iodopropynyl butylcarbamate (IPBC) is a fungicide used in wood preservation, particularly for timber that will be used in damp conditions.
64 - Propiconazole + Tebuconazole
A combination of fungicides, this preservative is effective against a wide range of wood-destroying fungi.
70 - Permethrin
A synthetic insecticide, Permethrin is used to protect timber from insect damage, particularly termites.
90 - Alkaline Copper Quaternary (ACQ)
An environmentally friendly preservative, ACQ is a popular choice for residential projects as it protects against both decay and insects without the use of arsenic.
Check Your Preservative Numbers
Before purchasing treated timber, it’s essential to verify the preservative code to ensure the wood is suitable for your project. Using the wrong type of treated timber could result in premature decay, insect infestation, or even structural failure.
To check the preservative code, look for the branding on the wood itself, where the code is usually listed along with other important information such as the hazard class and WOODmark® certification. Understanding these codes allows you to make informed decisions and ensures that your timber will perform as expected.
If you’re uncertain about a code or its meaning, consult this guide or seek advice from a timber supplier or professional.
Useful Resources
Check out our Resources page for other useful information regarding the preservation of timber.