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
Hardwood
  • Overview

    • 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
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    Tangential : Provides a simplified rating for tangential shrinkage. This is the measure of the percentage reduction in dimension from the unseasoned to 12% moisture content condition.
    6.10%

    Radial : Radial shrinkage is perpendicular to the growth rings. It is shrinkage in the direction towards the centre of the tree. Measurement is % value
    4.30%

    Unit Movement Tangential: This is the percentage of dimensional change for each 1% moisture content change between about 3% moisture content and the fibre saturation point for the particular species.
    0.38%

    Unit Movement Radial: This is the percentage of dimensional change for each 1% moisture content change between about 3% moisture content and the fibre saturation point for the particular species.
    0.32%

    Strength Group Strength groups are given for unseasoned (S1-S7) and seasoned (SD1-SD8) timber in accordance with AS 2878. S1 and SD1 yield the highest strength and stiffness whereas S7 and SD8 yield the lowest.

    Very High

    High

    Reasonably High

    Medium High

    Medium

    Reasonably Low

    Low

    Very Low

    Unseasoned:

    S1

    S2

    S3

    S4

    S5

    S6

    S7

    S8
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    Seasoned:

    SD1

    SD2

    SD3

    SD4

    SD5

    SD6

    SD7

    SD8
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    Stress Grade A stress grade is defined in AS 1720 as the classification of timber for structural purposes by means of either visual or machine grading. The stress grade indicates the basic working stresses and stiffnesses to be used for structural design purposes. Measured in MPa.

    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 density is based on moisture content of 12%. Unseasoned density is an approximation as it depends on the moisture content at the time of measurement. Measured kg/m3.

    Seasoned:

    990kg/m3

    Unseasoned:

    1180kg/m3

    Joint Group The joint group is a classification of the strength of a species in joint design. The values are from 1 (very high strength) to 6 (very low strength).

    Very High

    High

    Reasonably High

    Medium

    Low

    Very Low

    Unseasoned:

    J1

    J2

    J3

    J4

    J5

    J6
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    Seasoned:

    JD1

    JD2

    JD3

    JD4

    JD5

    JD6
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    Colour The colour of seasoned heartwood can vary between species and often within a species. The information provided should be used as a general guide only. In most cases, the colour of sapwood is either a lighter shade of the heartwood or a white/cream colour.

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

    Modulus of Rupture - Unseasoned: This property is a measure of maximum stress which timber can momentarily sustain when loaded slowly and continuously as a beam. Measured in MPa.
    98

    Modulus of Rupture - Seasoned: This property is a measure of maximum stress which timber can momentarily sustain when loaded slowly and continuously as a beam. Measured in MPa.
    142

    Modulus of Elasticity - Unseasoned: This property is of importance in determining the deflection of a beam under load — the greater the stiffness, the less the deflection. Measured in GPa.
    16

    Modulus of Elasticity - Seasoned: This property is of importance in determining the deflection of a beam under load — the greater the stiffness, the less the deflection. Measured in GPa.
    19

    Maximum Crushing Strength - Unseasoned:

    Also referred to as compression strength. This property measures the ability of the timber to withstand loads applied on the end grain. Measured in MPa.
    53

    Maximum Crushing Strength - Seasoned: Also referred to as compression strength. This property measures the ability of the timber to withstand loads applied on the end grain. Measured in MPa.
    76

    Impact - Unseasoned: Provides the Izod value, which is the energy taken in joules (J) to fracture the timber.
    23

    Impact - Seasoned: Provides the Izod value, which is the energy taken in joules (J) to fracture the timber.
    24

    Toughness - Unseasoned: This is a measure of timber’s ability to resist shocks and blows, and is synonymous with impact strength. It is measured in Nm.
    High - 25 Nm and above

    Toughness - Seasoned: This is a measure of timber’s ability to resist shocks and blows, and is synonymous with impact strength. It is measured in Nm.
    High - 25 Nm and above

    Hardness - Unseasoned: Refers to the Janka hardness test and is a measure of timber’s resistance to indentation.
    8.8

    Hardness - Seasoned: Refers to the Janka hardness test and is a measure of timber’s resistance to indentation.
    10.1

    Durability

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

    In-Ground: Durability is defined as the inherent resistance of a timber species to decay, or to insect or marine borer attack. All references to durability refer to the heartwood only. A scale of low to high (durability class 4 = low; 1 = high) has been adapted for above and in-ground durability.

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

    Above ground: Durability is defined as the inherent resistance of a timber species to decay, or to insect or marine borer attack. All references to durability refer to the heartwood only. A scale of low to high (durability class 4 = low; 1 = high) has been adapted for above and in-ground durability.

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

    Marine Borer Resistance: Indicates whether a species is resistant (R) or not resistant (NR) to marine borer attack.

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    Lyctid Borer Susceptibility: Indicates whether a species is susceptible (S) or not susceptible (NS) to lyctid borer attack.

    Susceptible

    Lyctid Borer Susceptibility - Other:

    Termite Resistance: Indicates whether a species is resistant (R) or not resistant (NR) to termites.

    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: A measure of the tendency of a material to ignite measured on a scale of 0 – 20. An index of 0 indicates that the material did not ignite during the 20 minutes that the test takes. An index of 20 indicates that the material ignited in the first minute.
    0 1 2 3 4 5 6 7 8 9 10

    EFH Spread-of-Flame Index: This is a material's propensity to burn rapidly and spread flames based on a scale of 0 to 10 where 0 means that the materials will not cause flames to reach the ceiling and 10 indicates that the material could be expected to cause flames to reach the ceiling of a room within 10 seconds of ignition.

    EFH Smoke-Developed Index:This is a measure of the concentration (measured by optical density) of smoke a material emits as it burns. It is based on an arbitrary scale of 0 to 10. The higher the index, the greater the hazard from smoke is likely to be.

    Critical Radiance Flux - Lower: This measures the radiant (heat) energy required to sustain burning. It is used in Australia to regulate floor coverings. The requirements are set out in BCA Specification C1.10a, providing CRF values for floor coverings based on Class of building, the location within the building (general use or use in fire isolated exits) and whether or not the building is sprinkler protected or not. CRF is measured in kW/m2.

    >2.2 and <4.5

    Critical Radiance Flux - Higher: This measures the radiant (heat) energy required to sustain burning. It is used in Australia to regulate floor coverings. The requirements are set out in BCA Specification C1.10a, providing CRF values for floor coverings based on Class of building, the location within the building (general use or use in fire isolated exits) and whether or not the building is sprinkler protected or not. CRF is measured in kW/m2.

    ≥4.5

    Smoke Development Rate: This is the speed at which smoke increases as determined by testing flooring materials in accordance with AS ISO 9239.1. The rate is expressed in terms of percent/minutes. For buildings not protected with a sprinkler system, a maximum smoke development rate of 750 percent/minute applies.
    <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: This value is determined by the volume of smoke measured over the mass loss of the tested sample per test carried out in accordance with ‘Cone Calorimeter Test’ AS/NZS 3837. It is measured in units of m2/kg.
    <250

    Bushfire Resistance: Naturally bushfire-resisting timbers are those with inherent bushfire-resisting properties. Some species have been tested and a number are in the process of being tested and are measured by Bushfire Attack level (BAL). BAL -12.5: Ember attack, BAL – 19: Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux between 12.5 and 19 kWm3, BAL – 29: Increasing levels of ember attack and burning debris ignited by windborne embers together with increasing heat flux between 19 and 29 kWm3.
    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
    a large room with rows of chairs

    Portal Frames

    For buildings that require large spans and column free interiors, timber portal frames provide one of the most aesthetically pleasing solutions. Utilising modern engineering technology, portal frame design transforms timber into a highly effective, efficient and economical structural product.
    a deck with a pool and a deck with a couch and a bench

    Decking

    Timber decking creates spaces that are functional, practical and aesthetically pleasing. With the right design and care a timber deck will make a valuable addition to any home or business, creating an outdoor living space that will be enjoyed for years to come.
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    Mouldings

    Mouldings are extremely versatile and durable, enhancing the aesthetics of any interior and functioning as the icing on the cake for designs with a focus on beauty and splendour.
    a wooden fenced hillside with plants and a fenced yard

    Retaining Walls (Landscaping)

    When it comes to retaining wall, landscape design and construction, timber is the natural choice. A material that is durable, sturdy and reliable, it has natural aesthetics that help it blend seamlessly with the outdoors. Careful consideration during the specification and design process will facilitate the creation of a long lasting, durable and beautiful timber retaining wall that will complement its surrounding landscape for years to come.
    a wooden stairs with railings

    Stairs, Exterior

    For outdoor applications, timber is one of the leading material choices. Timber use in external staircase applications creates structures of strength and durability, sheathed in a natural beauty that blends seamlessly with the outdoor environment.
    a staircase in a building

    Stairs, Interior

    Timber is the material of choice for designers seeking internal staircases of strength, beauty and durability.
    a patio with a deck and chairs

    Pergolas

    A timber pergola is a practical, functional and attractive way to extend living and entertainment spaces into the outdoors.
    a house with a pool in the back

    Rails and Balustrades, Exterior

    This provides general information on member sizes, connections and suitable materials for construction of handrails and balustrades in external applications. Commonly built from treated softwood and durable hardwoods, they can be finished with a wide variety of paints or stains, creating balustrades that with the right care and attention, will comfortably withstand the elements for decades to come.
    a close-up of a building

    Cladding, External

    The natural appeal, versatility and strength of timber makes it the superior choice for external cladding. Through specification, planning, design and finishing processes, timber cladding not only creates a building of superior strength, acoustic and thermal performance but also creates a place of beauty, style and natural appeal.
    a room with tables and chairs

    Structural Timber Poles

    Timber poles are utilised in structural construction to provide support for gravity loads and resistance against lateral forces. Not only serving a structural function, timber poles provide many aesthetic benefits, with their use in construction often complementing architectural designs aimed at harmonisation with the natural environment.
    a room with benches and paintings on the wall

    Flooring

    The warmth, strength and natural beauty of timber flooring is enduringly popular in a wide variety of domestic, commercial and industrial applications.

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