Gum, Yellow

Yellow gum is a medium sized native Australian hardwood valued for its toughness and durability. It is an ideal choice for heavy construction.

Other Names

Blue Gum, White Ironbark, South Australian Blue Gum, Large Fruited Blue Gum, Water Gum

Botanical Name

Eucalyptus leucoxylon

Common Form
Sawn
Species Type
Hardwood
  • Overview

    • Yellow gum or Eucalyptus leucoxylon is a medium sized hardwood that grows to about twenty metres in height. It is difficult to describe yellow gum as a single tree type, as there are many different sub-species, each with its own appearance and habitat. In general, trees of this species are noted for their long flowering period and attractive bark, which is dark and fibrous at the base of the trunk. The remainder of the trunk is smooth, grey, mottled yellow or white and bluish-grey on the upper trunk and branches.

    The overall species has a native range extending from southern NSW through central and western Victoria into most of South Australia, including Kangaroo Island. Yellow gum is suited to most areas except the tropics and adapts to most soils. It is drought and frost tolerant, and moderately fast growing. It also tolerates smog.

    Yellow gum timbers are prized for their hardness, durability and impressive structural properties. Its vast range and availability make it an appealing choice for those requiring timber for heavy construction purposes. Common uses include heavy construction as posts, wharfage, bridgework, sleepers and fencing.

    The timber is also termite resistant, although the sapwood is prone to lyctid borer. Workability is sacrificed for durability, as the timber is extremely dense and heavy. For this reason, it is not well suited to cabinetry.

    Yellow gum timber ranges in colour from yellow to pale brown. Grain is interlocked with a moderately coarse texture and often produces an attractive fiddleback figure.

    Yellow gum is often used in gardening as a screen, for windbreaks, and for displays of long-lasting, attractive flowers. It can be used to produce fine honey.

    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.
    6.30%

    Radial : Radial shrinkage is perpendicular to the growth rings. It is shrinkage in the direction towards the centre of the tree. Measurement is % value
    2.80%

    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.
    0.32%

    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.
    0.19%

    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:

    F14

    F11

    F8

    F7

    F5

    Seasoned:

    F14

    F11

    F8

    F7

    F5

    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:

    1010kg/m3

    Unseasoned:

    1200kg/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.
    87

    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.
    111

    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.
    11

    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.
    12

    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.
    44

    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.
    67

    Impact - Unseasoned: Provides the Izod value, which is the energy taken in joules (J) to fracture the timber.
    17

    Impact - Seasoned: Provides the Izod value, which is the energy taken in joules (J) to fracture the timber.
    9

    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.
    9.1

    Hardness - Seasoned: Refers to the Janka hardness test and is a measure of timber’s resistance to indentation.
    11.6

    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

    The heartwood of the yellow gum is, as its name suggests, yellow to pale brown in colour. It is common for the heartwood to exhibit pink and yellow tints around features. Sapwood is slightly paler and easily distinguished from the heartwood.

    Due to the high density of this moderately fast growing timber, yellow gum features an interlocked grain and a somewhat coarse texture. It often produces an attractive fiddleback figure.

    Common Applications

    Yellow gum timbers are prized for being hard, strong and very durable. This is an ideal timber for structural engineering purposes, including fencing and building. Timber of the Eucalyptus leucoxylon is used for sleepers and poles and is well suited to heavy construction such as wharfage and bridgework.

    Yellow gum timber is also ideal for use as fuel as it burns with few sparks and makes excellent coals. However, its density and hardness make it very difficult to split, and it is also tough to ignite.

    Workability

    Yellow gum is a very heavy, durable timber. It has a high rating in all classifications. Timber of this species dries to about 1000kgs/m3 (66lbs/ft3). The in-ground durability of Yellow gum timber is class 2, as is its above ground durability. Yellow gum heartwood is resistant to termites, but its sapwood is susceptible to lyctid borer.

    When timbers are as hard and heavy as yellow gum, they are very hard to work. Cutter angles on planes need to be reduced. Pre-boring for fixings is considered mandatory. The timber can be glued, but it is best to do this immediately after dressing. It sands and polishes to a superb finish and accepts preservative impregnation.

    Origin of timber
    VIC
    Readily Available
    VIC
    Yellow gum has limited availability in western Victoria extending into southern South Australia.
    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 wooden structure in a building

    Shear walls

    Lateral loads such as wind or earthquake on framed timber buildings - either post and beam or stud and joist - need to be resisted and shear walls and diaphragms offer an effective and economical solution.
    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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