Ironbark — Eucalyptus paniculata / E. sideroxylon
Two of Australia's hardest and most durable hardwoods. Grey Ironbark (Eucalyptus paniculata) is Strength Group SD1 seasoned — the top tier — and Red Ironbark (E. sideroxylon) is SD3. Both are Class 1 above-ground durability with Janka hardness from 11 to 16 kN, putting them among the hardest commercial timbers in the world. Native to the east coast from southern NSW to far north Queensland.
Ironbark products
Decking, cladding, screens, flooring, lining, battens, structural timber. Class 1 Australian hardwood — top tier durability.
Technical ReferenceSummary
Ironbark covers two related Australian hardwood species — Grey Ironbark (Eucalyptus paniculata) and Red Ironbark (E. sideroxylon) — both native to the east coast of Australia. They sit at the top of the AS 5604 natural durability scale and rank among the hardest commercial timbers worldwide. Used since colonial times for railway sleepers, bridges, wharves, and any application demanding extreme density and decay resistance.
Grey Ironbark is the structural workhorse — Strength Group SD1 seasoned (S1 unseasoned), Joint Group JD1 (J1 unseasoned), F-grade F34 seasoned. Density 1106 kg/m³ air-dry. Janka 16 kN seasoned. Red Ironbark is slightly lighter but still exceptional — SD3 seasoned (S2 unseasoned), JD1 (J1), F27 seasoned. Density 1050 kg/m³. Janka 11.9 kN seasoned. Both Class 1 above ground. Grey Ironbark heartwood is Lyctus-immune; Red Ironbark sapwood is Lyctus-susceptible. Both heartwoods termite-resistant. BCA Group 4. BAL 12.5/19/29 approved.
Class 1 of 4
Character & Appearance
Grey Ironbark heartwood is pale brown to dark chocolate brown, occasionally with a slight grey cast. Red Ironbark is dark red to deep red-brown — sometimes nearly black at the heart. Sapwood on both is much paler — pale brown to almost white — and is visually distinct from heartwood.
Grain is generally interlocked on both species, which produces a ribbon figure on quarter-sawn boards. Texture is moderately coarse but even. The high density and natural oil content means both species are difficult to work — pre-drilling for fasteners is essential. Once installed, both finish beautifully and develop a deep patina with age.
Species & General Properties
Mechanical & Physical Properties
| Property | Grey Ironbark | Red Ironbark |
|---|---|---|
| Density seasoned | 1106 kg/m³ | 1050 kg/m³ |
| Density unseasoned | 1170 kg/m³ | 1160 kg/m³ |
| Janka hardness seasoned | 16 kN | 11.9 kN |
| Janka hardness unseasoned | 11 kN | 10.7 kN |
| MOR seasoned | 185 MPa | 149 MPa |
| MOR unseasoned | 121 MPa | 107 MPa |
| MOE seasoned | 23 GPa | 17 GPa |
| Strength Group seasoned | SD1 | SD3 |
| Strength Group unseasoned | S1 | S2 |
| Stress Grade (Structural No.1) seasoned | F34 | F27 |
| Stress Grade unseasoned | F22 | F27 |
| Joint Group seasoned | JD1 | JD1 |
| Shrinkage (Total) | Value |
|---|---|
| Tangential shrinkage (Grey / Red) | 7.50% / 6.30 % |
| Radial shrinkage (Grey / Red) | 4.70% / 3.50 % |
Recommended Applications
Ironbark — both Grey and Red — is the timber of choice for applications demanding the highest combination of strength, density and natural durability. From colonial-era bridges and wharves through to contemporary architectural cladding and screens, it sits at the top of the Australian hardwood spec sheet.
Specification Notes
- Natural durability ratings apply to heartwood only. Sapwood requires Lyctus treatment (Red Ironbark especially) and is not naturally durable.
- Recommended spec wording for Grey: "Grey Ironbark (Eucalyptus paniculata) heartwood — AS 5604 Class 1 above-ground durability, Strength Group SD1 seasoned, Joint Group JD1 seasoned, F-grade F34 seasoned typical."
- Recommended spec wording for Red: "Red Ironbark (Eucalyptus sideroxylon) heartwood — AS 5604 Class 1 above-ground durability, Strength Group SD3 seasoned, Joint Group JD1 seasoned, F-grade F27 seasoned typical."
- Working note: Both Ironbark species are extremely dense and hard. Pre-drilling for fasteners is essential. Carbide-tipped tooling recommended for machining.
- Bushfire performance: BCA Group 4 fire rating, AS 3959 approved for BAL 12.5, 19 and 29 at thicknesses ≥18mm.
- Termite resistance in heartwood of both species — an additional benefit for exterior applications.
References
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Australia's hardest commercial timber. Decking, cladding, structural, screens — we hold and source both Grey and Red Ironbark for residential and commercial work. Send us your specs.