Decking
Best Hardwood Decking for Queensland: Spotted Gum vs Blackbutt vs Merbau (2026)
12 May 2026 · 7 min read
Choosing decking timber in Queensland isn't really a style question — it's a durability question dressed up as one. The Sunshine Coast climate (UV, humidity, sudden storms, salt within 5km of the beach) is brutal on the wrong species and gentle on the right ones. After a decade of building outdoor projects from Caloundra to Cooroy, here's how we actually pick a decking timber on site.
The Shortlist: Five Timbers Worth Considering
These are the species we specify by default. Anything outside this list usually falls down on durability, availability, or both.
| Species | Durability class | Hardness (Janka) | Typical lifespan in QLD |
|---|---|---|---|
| Spotted Gum | Class 1 (above ground) | 11.0 | 25+ years |
| Blackbutt | Class 1 | 9.1 | 25+ years |
| Ironbark | Class 1 | 14.0 | 30+ years |
| Merbau | Class 2 | 8.6 | 15–20 years |
| Treated Pine | Class 4 (treated to H3) | 3.6 | 10–15 years (substructure only) |
Our Default: Spotted Gum
If we had to pick one timber for 90% of Sunshine Coast decks, it would be spotted gum. It's Class 1 durability, locally available, weathers to a beautiful silver if left untreated, and oils up to a warm honey when finished.
It's also stable. Spotted gum doesn't cup, twist or split the way merbau or untreated softwood can in the Queensland summer.
When we don't recommend spotted gum
Pool surrounds with constant chlorine splash, and budget-driven jobs where the client genuinely understands and accepts a shorter lifespan.
Blackbutt — The Best All-Rounder
Blackbutt is our second pick and often interchangeable with spotted gum. It's a touch softer (Janka 9.1 vs 11.0) but takes finish beautifully and runs slightly cheaper.
Blackbutt is also one of the few hardwoods rated bushfire-resistant (BAL-29), which matters in hinterland builds around Maleny and Mapleton.
Merbau — Cheaper, But With Trade-Offs
Merbau is the most common 'budget hardwood' on hardware-store shelves. It works — but it bleeds tannins for the first 12 months, stains everything below it, and only reaches about two-thirds the lifespan of spotted gum.
Pros
- Roughly 25% cheaper per linear metre than spotted gum
- Widely available with short lead times
- Stable and easy to work
Cons
- Heavy tannin bleed — needs a sealed substructure and not over light pavers
- Shorter lifespan in coastal salt air
- Most merbau is imported — sustainability concerns for clients who care
Treated Pine — Substructure Only
Treated pine has a place — and that place is under your deck, not on top of it. H3-treated pine substructure paired with a hardwood deck top is a perfectly legitimate, cost-effective build. Treated pine as the visible decking surface is a false economy we won't quote.
Composite — When Real Timber Isn't the Right Call
Capped composite (Modwood, Trex, NewTechWood) is genuinely good now. It's the right call for pool surrounds, north-facing decks in full sun all day, and clients who explicitly want zero maintenance.
It's not the right call when you want real timber character, when the deck is the visual hero of the home, or when resale appeal matters more than maintenance hours.
How to Match Timber to Your Location
Coastal, hinterland and inland builds have noticeably different needs. We adjust the recommendation based on a 5-minute conversation about where the deck sits and how the sun tracks across it.
Within 5km of the coast
Spotted gum or blackbutt with stainless fixings. Avoid merbau and any galvanised fasteners — salt will reach them.
Hinterland (Maleny, Mapleton, Montville)
Blackbutt for bushfire rating, or spotted gum for the warmer tone. Both handle hinterland dew and cooler nights well.
Full-sun, west-facing decks
Composite is worth genuinely considering — hardwood in full afternoon QLD sun needs oiling every 9–12 months instead of the usual 18.
FAQ
Frequently asked questions.
What's the longest-lasting decking timber in Queensland?
Ironbark, comfortably. A properly built ironbark deck will last 30+ years in QLD conditions, though it's harder to source and around 20% more expensive than spotted gum.
How often does a hardwood deck need oiling?
Every 12–18 months for spotted gum and blackbutt, or every 9–12 months for full-sun, west-facing decks. Cup or splinter formation is the practical signal you've left it too long.
Can I leave my hardwood deck to silver naturally?
Yes — and a lot of our hinterland clients do. The timber lasts just as long, but you lose the warm tone and the surface becomes more porous over time.
Is spotted gum sustainable?
Almost all spotted gum sold in Queensland is locally grown and FSC-certified. We can supply a chain-of-custody certificate on request for clients who want it documented.
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