It’s the process that can dramatically improve timber durability and lower your lifetime costs. Here’s how to choose the right timber treatment.

Australia has one of the most comprehensive timber treatment standards in the world. Legislated across a region stretching from the Tropical North to the Snowy Mountains, from the dry interior to Tasmania’s wet and windy coast, Australian Standard AS 1604 means our timbers represent a quality, reliable product that can stand up to the various fungi, borers and termites that threaten them.

The standard itself is easy to follow, yet too often end users aren’t selecting the most appropriate options for their purpose. Jack Norton, secretary of the Timber Preservers Association of Australia (TPAA) says: “If I could make one change in the Australian timber industry it would be educating end users about choosing material that’s fit for purpose.”

Education is key

The problem doesn’t lie with timber suppliers. “I was in a hardware chain store and heard a worker give a textbook description of what timbers and treatments were appropriate for various uses,” Norton says. “But when he’d finished, the tradie buying from him asked, ‘Which one’s cheaper?’ Until we can convince people to buy timbers fit for purpose, this problem will persist.”

Poorly chosen timbers erode consumer’s faith, as failures in unfit materials are seen as being flaws in timber, rather than buyer error. This is happening at a time when timber represents one of our best carbon storage options and should be a larger part of the market.

Many of our most durable timbers are expensive, whether through scarcity or additional costs involved in working and transporting naturally durable species, which are generally heavier and resistant to tools as well as decay. But cheaper and lighter timbers can be made to emulate more durable varieties through the application of appropriate treatments.

“Treated timbers can fill the market gap for durable but affordable options,” says Norton. “Customers can rely on a timber’s brand.”

He doesn’t just mean using a reputable supplier. The brand is a three-part code affixed to each length of treated timber. The first part of the code tells you where the timber was treated, the second part is the preservative treatment code number, and the third part is the hazard class, which may have a suffix to indicate penetration, preservative or utilisation restrictions. A full explanation of brand codes is at

Timber treaters

While some treatment processes are simple enough for small-scale production, most involve larger business relationships between treatment chemical companies, timber mills and timber retailers. As an example, Outdoor Timbers in Melbourne works closely with the team at Lonza Wood Protection, who both supply and advise on specialty treatment chemicals, and also with AKD Softwoods forest products company, which provides sustainable timber products and processing services.

Most products available on the Australian market come with a similarly trustworthy pedigree. Koppers Performance Chemicals is another internationally recognised chemical supplier that is a large player in the local market. The brand code allows end users to see who the supplier is and check reviews of their product.

Hazard classes

Describing the conditions each piece of timber will be exposed to, the six main hazard classes range from protected interior sites (H1) where materials need only be able to resist flying insects, through to the toughest exterior conditions (H6) where the timber needs to survive constant moisture and marine organisms.

While some timbers, such as ironwood, are naturally durable enough to use in most conditions, preservative treatment means that cheaper, less naturally durable timbers can be used in higher hazard classes.

Used in conjunction with design that minimises risk and physical barriers, choosing timbers appropriate for hazard class will combat damp and infestation for decades.

Hazard class
ExposureBiological hazard
H1Inside, above groundLyctid borers
H2Inside, above groundBorers and termites
H3Outside, above groundModerate decay, borers and termites
H4Outside, in-groundSevere decay, borers and termites
H5Outside, in-ground contact with or in fresh waterVery severe decay, borers and termites
H6Marine watersMarine wood borers and decay

Preservative treatments

Most treatments currently on the market work by impregnating the timber’s exterior sapwood using pressure or vacuum created in a specialised chamber and liquid (water or solvent) to push preservative through the same cellular pathways that once carried the tree’s sap.

Others are applied as a coating that penetrates less deeply into the sapwood – an envelope treatment that is an economical alternative for interior uses – or in brush-on or glue-line applications. For a comprehensive list, see

Treatment does not affect the heartwood of the timber, where the cellular pathways are blocked up by the timber’s own growth process to form the structural heart of the tree. For this reason, timbers with low-durability heartwood, such as radiata pine, should not be used in high hazard situations.

Some treatments are sold under brand names rather than by treatment type, such as Hyne Timber’s T2 Blue, T2 Red, T3 Green and T3 Green Plus. These carry treatment brands that allow you to decode the treatment used, however the company’s product sheets  are even simpler for users to follow – a promise Hyne backs up with an up to 25-year guarantee.

“If you install our products correctly, any Hyne Timber product that becomes structurally unserviceable due to termite attack will be repaired or replaced at no cost to the homeowner,” says Shanelle Helmstedt, JOB TITLE TO COME.

The following represent the majority of treatments available in Australia.


For many years, Chromated Copper Arsenate (CCA) treatment was the major option available. A water-borne solution that is applied through pressure, it turns the treated wood green and results in a cheap and extremely durable product (up to H6 with other treatments). Copper is a high-quality protectant against decay and termites, while arsenic acts as a strong biocide. The chromium works as a fixative.

However, in 2006 CCA treated timber was banned in the EU due to concerns with its arsenic content. In Australia it is restricted for use by the Australian Pesticides and Veterinary Medicines Authority to structures that won’t come in high contact with humans.

This means it can’t be used in, for example, play equipment, garden furniture or residential decking (see for a comprehensive list). The restrictions are precautionary: no children were found to have been adversely affected by CCA in the research done, detectable levels of arsenic were found in horses who habitually sucked timbers.

New treatments are available, but CCA’s high durability keeps it an attractive option for non-contact sub structures. Uncoated steel fastenings can cause black stains on CCA due to reaction with the preservative, so always use recommended fasteners.


Short for alkaline copper quartenary, ACQ is an arsenic-free alternative that turns timber a different shade of green. Its quarternary ammonia compound works as a biocide against borer and termite attack.

It provides a high-quality protection similar to CCA, but the treatment is corrosive to some metals, so hot-dipped galvanised, copper or stainless steel fittings need to be used with these timbers.


Another water-based arsenic-free copper formulation, Tanalith is popular in Europe for use around children and animals. The copper is mixed with a synthetic azole biocide that combats fungi and insect infestation. Like other water-borne treatments it’s applied under pressure and requires a drying process, but it’s non-corrosive, so you can use galvanised fittings.

“Tanalith E has an extra water-repellent added to the formulation to increase its lifespan,” says Alison Gebbing, sales manager at Outdoor Timber. “We use it to treat our Ecowood®, which provides a broad range of structural timbers. You can also add colour to the process, which delivers timbers pre-coloured. Our ColourWoodTM and Ecowood ranges are distributed in all states.”

Tanalised treatments are widely used for framing timbers and other H2-H3 applications. Uncoloured timbers treated with this process are a light natural green, which weathers to a warm brown. Tanalith does not affect metal fixings, but cut surfaces require protection with a brush-on treatment.


Using microscopic particles of copper suspended in water with azole biocides, micronised copper azole (MCA) processes see the copper penetrate deep into the timber’s cellular structure, providing a very effective and long-lasting treatment.

MicroPro® from Koppers Performance Chemicals is a leading MCA product. “We brought it out a few years ago,” says Nick Livanes, Business Development Manager at Kopppers PC. “In that time it’s been very successful as a decking and sleeper product. It’s naturally a light timber colour, or it can have a colour added for our brown MicroPro Sienna. Although there’s a price premium, customers recognise the worth of the extended lifespan and attractive colour.”

MicroPro has also garnered a series of environmental certifications. “It’s very compact to transport,” says Livanes, “which saves costs and fuel. And then the process itself is certified low-VOC and contains no solvents and little liquid, so there’s much less in the way of waste and the runoff is environmentally cleaner. This means it’s a better product for our staff to work with and it’s safe to use in applications around children.”

MCA timbers require no special fittings and cut surfaces generally retain protection. Available from H1 to H5, it’s used mostly in H4 and H5 applications, including decking and landscaping.


Light Organic Solvent Preservatives (LOSP) is a technology that sees the preservatives diluted in a light solvent for application. It uses less pressure and, unlike the above processes, doesn’t add to the moisture content of the timber. LOSP treatments usually contain a combination of insecticides and fungicides. Copper napthenate (CuN) is the only commonly used one that changes timber colour (to green), others may have markers added (such as blue framing).

The process has some major advantages. “There’s no longer the risk of swelling and there’s no need to re-dry,” says Outdoor Timber’s Alison Gebbing. “This provides dimensional stability during and after treatment, which is ideal for high-value and engineered wood products.”

Outdoor Timber stopped using arsenic treatments in 2005, but Gebbing describes the recent move to LOSP as having changed the fundamentals of their business: “Introducing Lonza Wood Protection’s Vascol® Azure, which is an advanced, low-odour LOSP preservative, has given us the edge and, along with our Tanalith processes, allowed us to take our business to the next level. It reduces demand on our kiln, so we’re able to produce a much broader range of timbers for landscaping and construction.”

The solvent-based process also allows purchasers to receive their product much faster. “If we have the timber in the yard, it can be treated and dispatched the next morning,’ says Gebbing.

Glue-line treatments

Engineered timbers are increasingly popular for their long, straight and strong qualities. Unlike the above processes that rely on natural qualities of the timber, engineered timbers introduce preservatives through the glues that are used in the laminating processes.

“We can treat these timbers to their end use at the time of production,” says Shanelle Helmstedt. “Timbers protected by their position in a building can be left untreated, which lowers the cost. For timbers in hazardous situations, we can introduce preservatives that meet H2 or H3 conditions during processing and they become an integral part of the engineered timber.”

Other treatments

Boron-based preservatives are used in timber framing for protection against borers and some also have termite protections that are suitable south of the Tropic of Capricorn. They are a cost-effective option that is particularly suited to green timber, but not suitable for applications where the timber will come into ground contact as the boron will leach out again.

Oil-borne preservatives are used for heavy-duty construction and marine applications. Creosote and pigment emulsified creosote are the two major options and are used with treated timbers and/or highly durable timbers.

Using treated timbers


For the most part, safety requirements in using treated timbers are identical to non-treated timbers. Wash hands before eating, use appropriate dust, skin and eye protection and wash clothes after working with treated timber. If using timbers with residual treatment on the outside, protective clothing should be worn (solvent resistant if necessary) and washed separately after use.


Some treatments require a brush-on preservative to retreat cuts; check with your supplier. All external timbers benefit from coating, whether paint, stains or clear finishes. Talk with your supplier about suitable coatings and maintenance. Although treatment vastly increases the durability of timber, it does not make it maintenance-free and an appropriate schedule will give your structures their longest possible life.


Treated timbers should not be burned or used around animals (eg sawdust as bedding). Check with your local authority about recommended disposal methods for your timber. For small domestic offcuts and sawdust, normal waste disposal is fine.

The future of timber treatment

While new preservative treatments are looking at solutions ranging from increased fire retarding qualities to cleaner waste products, some of the most practical innovations in the sector concern education.

The Queensland Government’s QTimber app ( allows residents of that state to enter their location and planned usage for a list of recommended timbers and treatments with indications of expected design life years.

Based on the industry standard Construction Timbers in Queensland (CTIQ), it presents the two-volume publication’s information in a format that can be accessed from a phone or tablet, using a simple series of drop-down menus. Other states are looking at developing similar products.

Over the past decade, government-funded research in facilities such as the CSIRO, State Forests of NSW and Queensland Forestry has disappeared. This year has brought better news, the University of Queensland and University of the Sunshine Coast have teamed up with timber industry group Forest and Wood Products Australia to form the National Centre for Timber Durability and Design Life.

“It’s a boon to research,” says Jack Norton. “The more data we can get on how timber performs in different microclimates, the more we can target the end-use situations. Ultimately we may be able to extract natural durability compounds from timbers and find a cost-effective way of applying them as treatments.”

Nick Livanes has a more immediate set of goals. “We and our competitors are looking to find better processes for species like Baltic timbers that are currently hard to treat. And in the next year or so you should see new LOSP formulations from us that will deliver even more durable products.

“But what we’d all like to manage is to successfully treat the heartwood of Radiata pine. I can’t tell you we’ve got the final solution, but we’re working on it. Whoever gets there first will reap the rewards.”