Spotted Gum
Corymbia citriodora
Botanical Corymbia maculata
Revision history
- — Data re-verified in site-wide audit (formulas, sources, durability classes)
- — Working properties and comparable-species data cross-checked against listed sources
About Spotted Gum
Spotted Gum (Corymbia citriodora) is a hard, wear-resistant timber that is heavy going on tools, with a Janka hardness of 2,473 lbf (11,000 N) and a density of about 0.85 g/cm³. It grows in Australia.
Radial 4.0% against tangential 6.0% is an unusually even T/R ratio of 1.50 — Spotted Gum shrinks close to uniformly, which is why it holds a flat panel in exterior joinery and cladding. Its fibre saturation point is near 25%. Below it the wood shrinks steadily — 6.0% tangential, 4.0% radial. Ordinary territory: design the gaps rather than hoping the finish will hold it.0% tangential against 4.0% radial, quartersawn stock will behave noticeably better than flatsawn.
At 850 kg/m³ a cubic metre of Spotted Gum weighs about 850 kg air-dry — that figure, the 6.0% tangential and 4.0% radial movement and the 2,473 lbf hardness are the three inputs the calculators below actually consume. Select Spotted Gum in any of them to get species-specific results for weight, moisture, shrinkage and hardness.
Working properties
How Spotted Gum behaves at the bench and on the machine, drawn from Australian timber-industry technical data and WoodSolutions species records.
Durability & use classification
Spotted Gum's durability is best stated precisely: it is rated Class 1 above ground and Class 2 in ground — the Class 2 figure shown in the spec panel above is the in-ground rating. It resists decay and termites, with 40+ years' service typical above ground. It is also one of the few hardwoods compliant to BAL-29 bushfire requirements untreated, and sections 18 mm thick or greater need no fire-retardant treatment in bushfire-prone construction.
Typical applications & suitability
Indoor Outdoor — A genuine dual-purpose hardwood: strong enough for heavy engineering (strength groups S2/SD2, stress grades to F34) and handsome enough for architectural feature work.
Documented end-uses: decking, cladding and flooring, structural framing, posts and poles, engineering work including wharves, bridges, railway sleepers, cross-arms and mining timbers, plus fine furniture, feature walls, charred cladding and tool handles.
Comparable species
Species closest to Spotted Gum by density, hardness, stiffness and bending strength, computed directly from the Vriksai species dataset rather than hand-picked.
Trade alternatives. Its closest Australian counterpart is Jarrah (redder, very durable), while Balau and Bangkirai occupy the same dense-decking niche from South-East Asia and Wenge matches it on density.
Alternatives to Spotted Gum
Spotted Gum measures 2,473 lbf Janka at 0.85 g/cm³, EN 350 durability Class 2, movement rated Excellent. Anything replacing Spotted Gum outdoors has to hold Class 2 durability and carry the load — so nothing below that class appears here, however well it matches on hardness. Read the numbers against the Janka scale and EN 350 durability classes.
For decking, marine work and structural exposure where the surface takes impact as well as weather. Expect slower machining, faster tool wear and more weight to handle on site.
Lighter sections, easier fixing and lower freight per m³ — while holding the exterior durability class. Useful where the spec is over-engineered for the actual load.
If Spotted Gum is unavailable and the specification cannot change, these are the nearest substitutes across hardness, density, movement, stiffness, bending strength and durability class together — not on any single property. Lower distance means a closer match.
Computed from measured properties only — hardness, density, movement, stiffness, bending strength and EN 350 class. Price, availability and appearance are never inputs. Figures are representative values, not consignment absolutes: two species within a few percent are equivalent until verified on the material. Full method and the rules the engine cannot break.
Substituting outdoors is a match on durability class and movement first. Colour and grain can be matched later; a wrong durability class shows up as a callback in three monsoons. Where two candidates are close, compare them directly before specifying.
Compare Spotted Gum side by side
The pairings below are the ones that actually come up in exterior and structural tendering. Every pairing shows the measured figures side by side; full matrix in the comparison index.
Calculators relevant to Spotted Gum
Sized for exterior and load-bearing work in Spotted Gum — spans, fixings, weathering gaps and freight weight. Full set in the tool index.
Understand the figures
Strength properties — MOR, MOE and what they govern · Durability & fire — EN 350 classes and E84 ratings · Thermal conductivity — k-value and insulation behaviour · ThermoWood species guide — Thermo-D/Thermo-S treatment classes.
Further reading. Wood moisture content explained · How to calculate board feet.
Common questions about Spotted Gum
unverified no published source for this figure · WD The Wood Database (Eric Meier) · WS WoodSolutions Australia (AS/NZS basis) · calc derived from the figures above · — no published source found
A note on the shrinkage figures. The radial and tangential values here follow Australian practice (WoodSolutions / AS-NZS), which quotes shrinkage green → 12% moisture content. The Wood Database quotes the same species green → oven-dry and gives 6.3% / 9.9% — about 60% larger on both axes. Neither is wrong; they measure to different end points, and the T/R ratio (which is what governs cupping) agrees at roughly 1.5 either way. If you are feeding these into a movement calculation that expects green → oven-dry figures, use the Wood Database numbers instead.