There’s nothing like relaxing on a great deck to get the most out of your summer season.

The season for taking full advantage of Australia’s outdoor living spaces is upon us. This time of year also traditionally marks the annual household ritual of “oiling the decks” in preparation for our most punishing weather – our harsh Australian summer sun.

But oiling the decks is the crowning glory of what is a lengthy and considered process of building a great deck. It’s a process which also takes into account not only factors such as durability, safety and aesthetics, but also our moral and economic responsibilities to the sustainability of our forests and our industry.

Spoilt for choice

When it comes to timbers, we are spoilt for choice. A number of timbers have been identified as excellent choices for decks – all durability Class 1 timbers – such as Tallowwood, Teak, Jarrah, Blackbutt, Spotted Gum, Ironbark and Stringybark.

“It is important to bear in mind that only certain species adapt well to decking,” says Leon Travis from Boral Timber. “Blackbutt is popular, but Boral’s whole range of hardwood decking is well suited to the Australian climate.”

Timber is divided into four natural durability classes, with Class 4 being the least durable. These are timbers that, when above-ground and exposed, may only have a service life of five to eight years, and when in-ground may not even last for five years. Examples are Oregon, untreated Radiata Pine and Ash such as Mountain and Alpine.

And with more and more homes combining indoors and out, a smooth transition between spaces can be achieved by using a decking timber that is not darker than the interior flooring. Travis says the direction of the interior flooring should also be a guide, with decking boards installed accordingly to help maintain consistent design and flow between indoors and out. Remember that if the deck is in addition to an existing home, joists run 90° to the bearers and the decking runs 90° to the joists.

Merbau is also a popular hardwood with a high density and durability, and as such is an excellent choice for outdoor applications such as decking. Another advantage of using hardwoods for exposed areas is their natural fire resistance, and Merbau is sufficiently fire retardant to meet Australian Standard AS 3959. Jacinta Colley, national account manager for Simmonds Lumber, says Merbau “can be used in bushfire-prone areas without any treatment, and requires little energy in production, making it an environmentally friendly choice.

“And as a supplier of independently certified and legally sourced Merbau timber products, Simmonds DNA Lumber® range is durable, kiln dried, stable and termite resistant,” she says. “It satisfies all of the requirements of the Australian Illegal Logging Prohibition Act 2012, and employs full-time quality controllers at its sawmill to ensure a high level of quality in every pack of timber.”

Peter Giosserano of STS Timber says the key features of Merbau cannot be ignored.

“Merbau has an inherent beauty, an above-ground durability rating of 25 to 40 years, and has a natural resistance to fungi and termites,” he says.

Merbau has been a favourite choice for decking in Australia for generations due to its beauty, stability and structural integrity.

As such, STS Timber has ensured it has ample supplies of responsibly-sourced Merbau decking for the 2017 high season, and with its suppliers’ stringent grading protocols, this ensures only the best select grade timber with no imperfections.

STS Timber stocks fully-sized Merbau decking in 70, 90 and 140mm widths, and comes with 20mm free overlength trim cover on every board to accommodate saw cuts. In addition to Merbau, STS Timber  also stocks treated pine decking.

STS Timber operates out of two sites, Dandenong and Woori Yallock, Victoria, both with fully functioning treatment plants and both offering CCA, ACQ and MicroPro Sienna options.

But decking doesn’t have to be from new timbers. Recycled timbers have a beauty all of their own, whether used in furniture, cladding, flooring or decking. And with more than 30 different profiles
and sizes available through Kennedy’s Reclaimed and Sustainable Architectural Timbers, there’s something there for any number of decking styles and tastes.

Providing a connection to the natural environment, Kennedy’s decking timbers feature in many award-winning projects here and overseas. Our stunning cover this issue features a Martin Place rooftop, where warmth and character were added to an inner-city Sydney landscape of concrete and steel using spotted gum for the main decking and recycled grey ironbark for the landscaping features.

Kennedy’s timber comes in a range of sizes and finishes – such as sawn, dressed, brushed, anti-slip, smoky grey and aged, weathered timbers – and is suitable for use in residential or commercial projects. Species include Grey Ironbark, Red Ironbark, Tallowwood, Spotted Gum and Blackbutt.

Modified timber

There are a number of modified timber decking materials available. For instance, thermally modified wood is wood that has been modified by a controlled “pyrolysis” (decomposition brought about by high temperatures) process to increase durability.

These modified timbers have been developed to deal with issues such as movement and water absorption that natural timbers can be prone to. Some also include a man-made component to further improve durability, largely doing away with many maintenance issues.

When choosing a material for a timber deck, beauty, strength and all-weather performance are important considerations. High-performance wood for decking, when adequately protected from the elements, is likely to stay flat and not warp, split or swell, or be affected by fungi, water uptake or rot. It is also crucial that the wood is non-toxic and therefore totally safe for people and pets. Accoya and Hyne’s T3 Green both meet these requirements.

Mathews Timber is a supplier of the revolutionary Accoya, “a fantastic timber”, according to Mathews Timber’s marketing manager Ben Mathews, a third generation Mathews family member involved in the business. “It is fast becoming the material of choice for all exterior applications.”

Accoya is a modified softwood – usually a Class 4 durability timber such as Radiata Pine – which has undergone an “acetylane” process to overcome some of a natural timber’s issues (see diagram).

Acetylation chemically modifies wood. One school of thought as to why acetylated wood resists decay is that acetylation changes the conformation of the substrate that fungi are trying to eat. The fungal enzymes that break down the wood don’t recognise it as food.

Essentially, the wood is modified uniformly through the cross section, not just at the surface, using concentrated vinegar and high pressure. This alters the cell structure of the timber, making it impervious to moisture.

“This results in a predictable exterior timber that does not buckle, crack or twist like traditional timbers can when used outside,” says Mathews.

The exceptional durability and dimensional stability mean that Accoya wood requires significantly less maintenance because coatings stay where they belong on the wood, with results showing coatings last up to three times as long.

Accoya has been proven in multiple tests against various fungal, termite and insect species in multiple regions to have improved performance, is resistant to salt and can be used around saltwater, for instance as marina decking. It is not recommended for permanent immersion in salt and brackish water as the acetylation treatment is not yet warranted for resistance against marine borers and other marine organisms. Accoya undergoes extensive testing by leading institutes around the world and is independently audited by organisations from USA, France and the Netherlands.

Hyne Timber’s T3 Green Plus is another modified timber for a range of outdoor projects, including decks and verandas and their bearers, joists, rafters, battens and beams. The revolutionary CodeMarkTM certified treatment penetrates both sapwood and heartwood fibres, providing superior protection to your structure. The natural and consistent treatment colour also produces a better-looking result when stained, which is becoming extremely popular.

Hyne Timber’s Marketing Manager Jeremy Mead says every piece of T3 Green Plus is scanned at least six different ways, in addition to stress-testing to ensure it meets the relevant Australian Standards for structural timber. It is available in both MGP10 and MGP12 grades.

“T3 Green Plus also has a lower net environmental impact than most other building materials, and unlike other low odour H3 treated products, T3 Green Plus has no VOC emissions, making it ideal for wet or humid areas with low ventilation – including indoors,” Mead says.

The treatment itself is free of hydrocarbon chemicals, making it one of the safest and most environmentally-friendly timber treatments available in the Australian market today. T3 Green Plus provides long-term protection against termite and fungal attack in above ground indoor and outdoor applications. It can be cut, notched and planed, but it does need to be resealed at these points with a fungal resistant preservative.

As well, Hyne Timber advises:

  • coat all surfaces with a paint or stain finish when used outdoors;
  • cover deck joists with a water resistant malthoid strip; and
  • ensure water can run off and cannot pool on the timber surface, especially in connections.

Hyne Timber’s Technical Data Sheet #8 (TDS 8) has more information about specific conditions and their requirements.

Facts about fasteners

Ensuring a deck is properly secured is essential for both durability considerations and safety. Incorrect fixing of a deck to its joists can cause problems such as water seeping into the timber via incorrectly finished joints and holes or splitting caused by fasteners, ultimately leading to rot.

Choosing the right fasteners for your deck isn’t an easy decision. After all, there are so many options to consider. Screws, nails, and anchoring hardware have to stand up to many years of use and abuse. Standard galvanised fasteners have a single protective coating, which may flake off and rust. Double-dipped galvanised fasteners are better protected, but you’ll get the best life from dedicated decking fasteners. Stainless steel is costly, but the best. It is recommended to use stainless steel fasteners with acetylated wood because residual acetic acid would corrode regular steel.

Common nails with thick shanks and large heads can be used but might work their way out; rink shank or spiral nails would be a better choice but are very difficult to remove should the need arise. Both are difficult to drive in and may split the wood.

Screws are likely to be a better option and come in many styles. Decking screws are generally coated for corrosion resistance when they are not stainless steel, and can be driven as fast as nails with the appropriate tool. It’s best to use screws with a square-head drive as the bit that does the driving is unlikely to slip out of the head and thus damage the screw head. Remember to drill a pilot hole.

You can avoid visible nails and screws completely with invisible deck fastening systems, which come in many forms. They are more expensive and more time-consuming to install, but they leave a clean, uncluttered deck surface. They are especially useful in contemporary designs or with complicated decking patterns because they don’t distract from the pattern of the decking itself.

Topping it off

A timber deck is a significant financial investment and needs to be maintained. Where oils are needed, ideally we should be looking for a long-lasting oil that is not only fast-drying, but one that nourishes and protects the timber from our extreme temperatures, whether 40°C in February or minus 10°C in July.

Water-based oils have less of an impact on the environment and also less of an impact on the colour of the wood. These water-based oils block the pores of the timber and cover the surface acrylic film.

Non-water-based oils aim to penetrate into the wood fibre, but also lay a film on the surface of the timber. Non-water-based oils tend to darken the colour of the wood somewhat and take a longer time to dry.

The choice between these two depends on three factors: the type of use of the deck, the timber used and the type of climate it’s likely to encounter (Darwin versus Hobart).

For more product information:


STS Timber:

Mathews Timber:

Hyne T3 Green: