Gum, Spotted

Spotted gum is a premium Australian hardwood that is used widely in structural, exterior and internal applications.

Other Names

Lemon-scented Gum, Spotted Irongum, Eucalyptus maculata, Corymbia citriodora, Eucalyptus citriodora, Corymbia henryi, Eucalyptus henryi

Botanical Name

Corymbia maculata, Corymbia citriodora and Corymbia henrii

Common Form
Sawn
Species Type

Spotted gum is one of Australia’s premium native hardwoods with a striking appearance and a high degree of natural durability and strength, making it an ideal timber for a variety of structural, exterior and interior applications. Architects and designers throughout the world value spotted gum timbers for their back-sawn grain structure, attractive markings and vibrant colour palette.

Spotted gum is the common name for four species that grow along the east coast of Australia, from northeast Victoria to the northern tablelands of Queensland, with some occurrence in western areas of southern Queensland. Sawn timber from these species is generally available throughout Australia. These species have straight, slender trunks with smooth bark that is shed in patches, giving the trees their characteristic spotted appearance.

 

The species referred to as spotted gum vary in appearance but not in durability class or other properties. The heartwood ranges from light brown through to dark red-brown hues. Sapwood is usually white to light brown in colour. The presence of a wavy grain can produce an attractive fiddle-back figure. The wood has a slightly greasy feel, a characteristic that aids machining and boring. Spotted Gum components that are 18mm thick or greater do not require fire retardant treatment for use in construction in bush-fire prone areas.

Spotted gum is used in engineering applications such as wharf and bridge construction, railway sleepers, cross-arms and mining timbers. It is suitable for a range of building applications, such as posts and poles, framing, flooring, lining, decking and cladding. Spotted gum is also used in the manufacture of veneer and plywood. Other applications include boatbuilding, tool and implement handles, polo sticks and diving boards. Compared to other Australian hardwoods, spotted gum is a minimal staining timber as it is less prone to bleed-through of tannins than other species. Spotted gum is also a good timber for carving and woodturning.

 

 

 

Shrinkage

Very Low Low Medium High Very High

Tangential :

6.10%

Radial :

4.30%

Unit Movement Tangential:

0.38%

Unit Movement Radial:

0.32%

Strength Group

Very High

High

Reasonably High

Medium High

Medium

Reasonably Low

Low

Very Low

Unseasoned:

S1

S2

S3

S4

S5

S6

S7

Seasoned:

SD1

SD2

SD3

SD4

SD5

SD6

SD7

SD8

Stress Grade

Structural
No. 1
Structural
No. 2
Structural
No. 3
Structural
No. 4
Structural
No. 5

Unseasoned:

F27

F17

F14

F11

F8

Seasoned:

F34

F27

F22

F17

F14

Density per Standard

Seasoned:

990kg/m3

Unseasoned:

1180kg/m3

Joint Group

Very High

High

Reasonably High

Medium

Low

Very Low

Unseasoned:

J1

J2

J3

J4

J5

J6

Seasoned:

JD1

JD2

JD3

JD4

JD5

JD6

Colour

  White, yellow, pale straw to light brown Pink to pink brown Light to dark red Brown, chocolate, mottled or streaky
   

Mechanical Properties

Modulus of Rupture - Unseasoned:

98

Modulus of Rupture - Seasoned:

142

Modulus of Elasticity - Unseasoned:

16

Modulus of Elasticity - Seasoned:

19

Maximum Crushing Strength - Unseasoned:

53

Maximum Crushing Strength - Seasoned:

76

Impact - Unseasoned:

23

Impact - Seasoned:

24

Toughness - Unseasoned:

High - 25 Nm and above

Toughness - Seasoned:

High - 25 Nm and above

Hardness - Unseasoned:

8.8

Hardness - Seasoned:

10.1

Durability

Low Moderate Reasonably High High
(0 - 5 yrs) (5 - 15 yrs) (15 - 25 yrs) (more than 25 yrs)

In-Ground:

(0 - 7 yrs) (7 - 15 yrs) (15 - 40 yrs) (More than 40 yrs)

Above ground:

(0 - 20 yrs, usually < 5) (21 - 40 yrs) (41 - 64 yrs) (More than 60 yrs)

Marine Borer Resistance:

Lyctid Borer Susceptibility:

Susceptible

Lyctid Borer Susceptibility - Other:

Termite Resistance:

Resistant

Fire Properties

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

EFH Ignitibility:

0 1 2 3 4 5 6 7 8 9 10

EFH Spread-of-Flame Index:

EFH Smoke-Developed Index:

Critical Radiance Flux - Lower:

>2.2 and <4.5

Critical Radiance Flux - Higher:

≥4.5

Smoke Development Rate:

<750
1 - non-combustible 2 - reasonably non-combustible 3 - slightly combustible 4 - combustible

Fire Properties Group
Number:

Group Number - Other:

For plywood: Fire Properties, EFH Spread-of-flame Index: 7

Average Specific Extinction Area:

<250

Bushfire Resistance:

BAL 12.5, 19 and 29 – All AS3959 required applications
Appearance

Spotted gum timbers are available in a range of colours depending on the location of the source forest. The heartwood ranges from light brown through definite browns to deep red-brown hues. Sapwood is white to light brown in colour and can be up to 50mm wide. Spotted gum is a moderately coarse and uneven textured wood with some timbers having the additional feature of a wavy grain, giving rise to an attractive fiddleback figure.

 

Common Applications

Spotted gum has a long history of use in engineering applications such as wharf and bridge construction, railway sleepers, cross-arms and mining timbers. It is used for a variety of applications, including structural building members, such as posts and poles, and for framing, flooring, lining, decking and cladding. It is also used in boatbuilding and is the primary Australian timber used for the handles of tools and implements that are subject to high impact forces. Spotted gum is a suitable carving and woodturning timber and is used in the manufacture of both indoor and outdoor furniture. Outdoor furniture in spotted gum has consistently won industry awards in Australia and is exported to destinations around the world.

 

Workability

Spotted gum machines well due to its natural greasiness and there is no difficulty using the timber with standard fittings and fastenings. As with most high-density species, machining and surface preparation should be done immediately before gluing. Spotted gum readily accepts paint, stains and polish. It has a lower tannin content than most other eucalypts, therefore staining of paintwork or brickwork as a result of water running over unpainted timber surfaces is less likely to occur.

 

Origin of timber
NSW
Readily Available
NSW
Sawn timber from these species is generally available throughout Australia, and spotted gum is currently the highest volume native hardwood harvested in Queensland. Spotted gum is exported to the US and a range of other destinations.
Source of timber
Native Forest
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