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Greybox Decking

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SKU: GHT-1929 Categories: Decking, Timber Decking Brand: Greenhill Timbers Product Brand: Green Hill Timbers Janka Rating: 15

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Grey Box decking in 86 × 19 mm and 135 × 19 mm: one of the hardest, most durable Australian decking timbers, with Janka hardness 15 kN and Class 1 durability both above ground and in-ground, rated for bushfire decking up to BAL-19.

Sizes: 86 × 19 mm and 135 × 19 mm in random lengths
Timber: Grey Box (Eucalyptus moluccana), grown from Jervis Bay in NSW to the Atherton Tableland; usually pale brown, sometimes yellowish; about 1105 kg/m³
Durability: Class 1 above ground, which the Queensland Government rates at more than 40 years’ expected life; Class 1 in-ground too; the heartwood is termite resistant
Bushfire: qualifies under AS 3959’s high-density rule for BAL-12.5 and BAL-19, but it is not on the bushfire-resisting timber list, so it can’t be used for decking at BAL-29. For BAL-29, choose Spotted Gum, Blackbutt or Merbau
Joist spacing: 450 mm centres, as WoodSolutions recommends for decking; its deck design guide allows up to 500 mm for 19 mm hardwood, or 350 mm if the boards run at 45°
Gaps: 3–4 mm between 86 mm boards and 4–5 mm between 135 mm boards at installation (WoodSolutions deck design guide)
How much for a deck: a 20 m² deck needs about 140 lineal metres of 135 mm board or about 225 lineal metres of 86 mm, plus about 10% for offcuts
Low decks: under 400 mm off the ground, WoodSolutions suggests 5–6 mm gaps and at least 40 mm between the deck and the house, for airflow
Fixing: two fixings per board at every joist, at least 12 mm from edges and ends. Pre-drill this dense hardwood. Use stainless steel within 1 km of the coast or 1 m of a pool. See our decking screws
Finishing: coat every face and cut end, ideally before fixing, then recoat at least once a year or as the oil maker directs (WoodSolutions); left bare, it weathers to silver-grey. Oils we stock: CUTEK CD50, Intergrain Universal Timber Oil or Sceney’s Timber Decking Oil
At Greenhill: stocked at 170 Settlement Road, Thomastown, with pickup or delivery across Melbourne and regional Victoria. Compare species on our hardwood decking page.

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Product Description

Greybox Timber Decking – Hardwearing Timber for Exposed Decks

A Tough Local Hardwood

Greybox isn’t one of the flashiest timbers, but it’s tough, consistent, and built to last. The high density gives it excellent resistance to wear, which is why it’s often used in decking that sees a lot of foot traffic or direct exposure. Once installed, it stays flat, doesn’t cup easily, and shrinks far less than softer species.

High Janka Rating and BAL Compliance

With a Janka rating of 15.0 kN, Greybox sits right near the top end of the hardwood scale. That puts it in the same league as Ironbark when it comes to dent resistance and surface durability. It qualifies for decking up to BAL-19 under AS 3959’s high-density rule. It is not on the bushfire-resisting timber list, so for BAL-29 sites choose Spotted Gum, Blackbutt or Merbau.

Built-in Resistance

One of the key benefits of Greybox is that it doesn’t rely on preservatives. It naturally resists termites and decay, making it useful in wet zones, pool decks, and shaded areas that don’t dry out quickly. It holds nails and screws well and doesn’t split much during installation.

A Neutral, Workable Appearance

You’ll find a mix of soft greys, light browns, and muted reds across a batch of Greybox. It’s not overly figured, so it works well when you want the deck to sit quietly in the background. Left to weather, it fades to a uniform grey. Oiled, it deepens slightly but stays subtle, great for designs that favour natural materials.

Shop for Greybox Decking: 135 x 19 and 86 x 19

At Greenhill Timbers, we supply random-length Greybox decking, most commonly in two sizes:

135 x 19 mm – for a wider board look and faster coverage
86 x 19 mm – for tighter joints and a more traditional profile

They are carefully selected to give you consistency across your run. Whether you’re working on a backyard rebuild or a large multi-dwelling project, we’ll help you calculate the quantities and line up delivery so things stay on track.

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Janka Rating

Greybox Decking — Janka hardness: 15 kN

What Is the Janka Rating?

The Janka rating is a way to measure how hard a timber is, specifically, how much force it takes to push a small steel ball halfway into the wood. The number you get is shown in kilonewtons (kN). A higher Janka score means a harder, more durable timber. Builders and floor installers use it to work out which timbers hold up better in busy areas.

Here’s a rough guide to how some timbers sit on the scale:

Brazilian Walnut – around 16.0 kN
Spotted Gum – roughly 11.0 kN
Tasmanian Oak – about 5.5 kN
Radiata Pine – close to 3.0 kN

Keep in mind: these values can vary depending on moisture content and grain direction.

It's One Part of the Decision

Hardness is useful to know, but it’s just one factor. Janka doesn’t tell you how a timber reacts to heat or humidity, how stable it is, or how easy it is to cut and install.

Some of the hardest woods can be difficult to work with. Others, even if softer, might be more stable or forgiving on-site.

At Greenhill Timbers, we look at the whole picture, not just the numbers. All our timbers are structurally graded and covered by a 25-year guarantee. We'll help you pick something that works for your project, not just on paper.

Delivery Options

Melbourne-Wide Delivery

We carefully prepare your order and organise pick-up or delivery that suits your schedule, ensuring your satisfaction when you choose to purchase from us. If you're located in Melbourne and its surrounding areas, you can collect your order from our Thomastown Showroom at 170 Settlement Road. Otherwise, we can facilitate delivery by leveraging our strong partnerships with various sub-contractors to get you the most competitive delivery rate and suitable time frame. For more information, get in touch with us.

Why Choose Us

Get Your Timber Packed

We pack, wrap and load your products into your vehicle on-site. As a Green Hill customer, you won’t have to pack your timber or lug it into your vehicle after you’ve purchased it.

One Stop Shop

We are a one-stop shop for all your timber needs. Get dozens of types of wood, both imported and local, and the right cuts for your decking, flooring, cladding and fencing projects.

Competitive Pricing

In most cases, we can help you save hundreds or even thousands of dollars on the same materials compared to other timber suppliers.

Expert Staff

Our expert staff will assist you in finding the perfect timber to match your projects based on a relaxed chat to find what you need.

Transparent Quotes

We give you the whole picture when we quote you. So you can avoid any nasty surprises down the line.