Gum, Sugar

Sugar gum timber has few defects and is prized for its durability and attractive light orange decorative finish, making it an excellent choice for both interior features and exterior construction.

Botanical Name

Eucalyptus cladocalyx

Common Form
Sawn
Species Type
Hardwood
  • Overview

    • Sugar gum, a chiefly plantation-grown native hardwood, produces a dense, blonde to tan timber that is both decorative and durable. This vigorous plantation species has a history of farm use for firewood and fencing. However, sugar gum has the capacity to produce higher value sawn timbers. Where good genetic material has been used in plantation, the form of the timber lends itself to sawlog production with minimal management requirements. CSIRO research rates sugar gum as the most outstanding species of the four native hardwood species grown in Victoria.

    This eucalypt originates in South Australia in three distinct populations: the Flinders Ranges, Eyre Peninsula and on Kangaroo Island. Sugar gums from the Flinders Ranges reach up to 35m in height and have the classic ‘gum' habit: a straight trunk with steep branches occurring about half way up. Eyre Peninsula and Kangaroo Island trees are much shorter and often have crooked trunks. Sugar gums are notable for their mottled yellow to orange bark and clusters of flowers grouped on leafless branchlets inside the tree crown. The old bark is smooth and grey, shedding in irregular patches to expose the fresh yellowy-brown bark.

    Timber harvested from sugar gum has little defect and is prized for its durability. It is particularly suited to situations requiring high strength where appearance is also important, such as flooring and joinery. Sugar gum polishes to a superb finish making it highly sought after for decorative applications. The timber can exhibit desirable grain features such as a bee's wing and fiddle-back figure, suitable for the production of high quality furniture and flooring. Its durability also makes it a valuable timber for exterior applications such as cladding, decking, outdoor furniture and pickets.

    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.
    10.50%

    Radial : Radial shrinkage is perpendicular to the growth rings. It is shrinkage in the direction towards the centre of the tree. Measurement is % value
    6.20%

    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.

    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.

    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:

    F17

    F14

    F11

    F8

    F7

    Seasoned:

    F27

    F22

    F17

    F14

    F11

    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:

    1105kg/m3

    Unseasoned:

    1190kg/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.
    73

    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.
    110

    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.
    12.4

    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.
    16

    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.
    36

    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.
    61

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

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

    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.

    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.

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

    Hardness - Seasoned: Refers to the Janka hardness test and is a measure of timber’s resistance to indentation.
    10

    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.

    		 Check mark
    (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.

    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

    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:

    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 and 19 – All AS3959 required applications
    Appearance

    Sugar gum has a fine, even texture and is often free of defect, due to the self-pruning nature of the species that leaves the main trunk free of knots and burls. It produces a blonde to tan timber that polishes to a light ginger-orange colour, with subtle greens and pinks brought out by finishing. The incidence of interlocking grain in certain trees creates the potential for timbers of this species to produce both bees wing and fiddle back figure to stunning affect. For colour, figure and durability, sugar gum timber is ideal.

    Common Applications

    Sugar gum has a class 1 durability rating. Its strength and resistance to wear make it suitable for use in quality indoor and outdoor furniture, flooring and decking, poles and posts, stair treads and benchtops.

    Despite its exceptional hardness, sugar gum's warm appearance and grain characteristics make it ideal for decorative purposes. The strength of the timber allows for joinery and fine furniture designs without compromising robustness. The timber polishes to a fine finish.

    Veneers created from sugar gum are an easy way to enjoy the beauty and warmth of timber while minimising its consumption. A range of architectural sugar gum veneer products are available.

    Strong and durable, sugar gum produces timber suitable for heavy construction purposes. It also produces structural timber of very high strength and low defect for use in the building trade as posts and beams.

     

    Workability

    Sugar gum timber air dries slowly and can also be kiln dried. Both forms of drying yield negligible surface checking or degradation. Some shrinkage and expansion occurs in service. Standard laying techniques for hardwood flooring should be used to manage movement. Although unfinished timber weathers to a silver grey and develops superficial checking, finished timber has excellent outdoor performance.

    Sugar gum is dense and difficult to work. It requires pre-drilling with a titanium coated bit to about 80% of the nail or screw diameter. Gluing should be done only on freshly machined surfaces using 'Titebond' aliphatic resin glue. Research has yet to prove if other glues can be used. Construction using biscuit-jointed corners, floating panels, and clip attached table and bench tops is preferred.

    Organic timber oils give the surface of sugar gum timber a dark honey colour. French polishing and synthetic two pot finishes are also used effectively.

     

    Origin of timber
    NSW
    Sugar gum timbers are relatively scarce, due mainly to the fact that the versatility of this timber has only recently been established. The relative scarcity of the timber and its high quality, coupled with the species’ ‘green’ plantation-grown credentials creates a strong market for this timber.
    Source of timber
    Native Forest
    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.

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