Timber preservatives: what is in treated pine and what it protects
The preservative is how the mill reaches the hazard class. The class is what tells you where the timber can go.
Why the preservative matters less than the hazard class
Most buyers ask which preservative is in the pine. The better question is which hazard class the pack is rated for. The class (H2 to H6 under AS 1604) tells you where the timber can go. The preservative is how the mill gets it there.
The main types you will see
| Type | What to know |
|---|---|
| Copper based (copper azole, ACQ) | Common in pine for outdoor and in-ground classes. Often gives a green tint |
| CCA (copper chrome arsenic) | Limited to specific uses in Australia. Check the label and the rules before choosing it |
| LOSP (light organic solvent) | Used on dry, above-ground timber such as framing and joinery. Little colour change |
| Boron | Dry use only, because it can wash out if the timber gets wet |
What a mill uses can change, so read the tag on the board rather than relying on this table for a purchase.
What the label does and does not promise
A treated timber label says the wood meets a standard for a class of use. It does not say termites will never touch it, and it does not cover the timber around it. The detail is in termite treated timber.
Treatment also depends on penetration. Cut a board and the middle may be less protected than the outside. That is why cut ends need a brush-on preservative.
Match the class to the job
- Inside, dry and protected: H2 timber, often framing.
- Outside, above the ground: H3 timber.
- In the ground: H4 or H5, depending on the load and the soil.
Do not buy a higher class than the job needs. Do not drop to a lower one on a post that carries weight. If the design names a class, use that one.
Handling and safety
Wear gloves and a dust mask when cutting treated pine, and do not burn offcuts. Follow the safety data sheet from the supplier. Disposal rules vary by state, so check with your local council or environment agency.
What to do if you find damage in the timber
If you see mud tubes, frass or a post that sounds hollow, do not spray it or break it open. Leave it as it is and book a licensed timber pest inspection. Any treatment is for a licensed pest management technician using APVMA registered products. This site does not certify any product or brand.
Frequently asked questions
What preservative is used in treated pine?
It varies by class and mill. Copper based preservatives are common for outdoor and in-ground pine, LOSP for dry framing, and boron for dry use only. Read the tag on the board.
Do timber preservatives stop termites?
They make the treated timber a poor food source, but they do not protect untreated timber nearby. Termites can still tube over treated wood to reach the house.
Can I paint preservative on untreated wood to make it H3 or H4?
No. Brush-on preservative helps seal cut ends, but it does not give the deep penetration that makes timber meet a hazard class.
Sources
What this page explains is based on these official sources. If you check one and it does not match what you read here, send it to us and the article gets corrected.
- Department of Health, Victoria. Pest control - termites
- Queensland Building and Construction Commission. Protect against termites - termite management systems and inspections
- Standards Australia. Australian Standards (AS 3660 termite management, AS 4349.3 timber pest inspection)