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Gum, Grey

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Grey gum is a medium-sized hardwood tree growing up to 40 metres in height and one metre in stem diameter. Varieties of grey gum occur along the east coast of Australia, from the Hawkesbury River in New South Wales as far north as Maryborough, and inland to the Carnarvon Ranges and Blackdown Tablelands in Queensland.

The heartwood of this species is a red to reddish-brown colour, visually distinct from the paler sapwood. Grain is usually interlocked, with a coarse but even texture. Grey gum is similar in general appearance to the ironbarks, but often marked by characteristic grub holes.

Grey gum timber is extremely durable, with an in-ground life expectancy in excess of 25 years. For aboveground applications, life expectancy exceeds 40 years. Grey gum heartwood is termite-resistant, and untreated sapwood is not susceptible to lyctid borer attack. Grey gum sapwood is readily impregnated with commercially available preservatives.

The timber is very hard, rated 1 on a 6-class scale in relation to both indentation and ease of working with hand tools. It machines well, although care is required in working the timber’s interlocked grain. Grey gum readily accepts paint, stain and polish, and is amenable to the use of standard fastenings and fittings. As with most high-density species, machining and surface preparation should be done immediately prior to the application of adhesives.

Grey gum is widely used in heavy engineering and marine construction, where it is found as poles, piles, railway sleepers, cross-arms and mining timbers. In general construction it is used for building framework, flooring and decking. Grey gum is also extensively used in landscaping and boat building. It is renowned for making superior-quality butcher’s blocks suitable for use in both commercial and domestic environments.

 

Appearance

The heartwood of this species is a red to red-brown colour, visually distinct from the paler sapwood. Grain is usually interlocked with a coarse but even texture. Grub holes are an occasional feature in sawn timber products.

 

Common Applications

Grey gum is widely used in heavy engineering and marine construction, where it is found as poles, piles, railway sleepers, cross-arms and mining timbers. In general construction it is used for building framework, flooring and decking.

Grey gum is also extensively used in landscaping and boat building. It is renowned for making quality butcher’s blocks for both commercial and domestic use.

Common Form

Sawn

Workability

Because of its density and grain structure, grey gum is difficult to work when dry. It machines satisfactorily, although care is required in working the timber’s interlocked grain. Grey gum readily accepts paint, stain and polish, and is amenable to the use of standard fastenings and fittings. As with most high-density species, machining and surface preparation should be done immediately prior to the application of bonding agents.

Origin of Timber

NSW

Readily Available

NSW

Availability - Further Information

Grey Gum timber products are readily available in New South Wales and Queensland.

Availability - Further Information

Native Forest

Shrinkage

Very Low Low Medium High Very High

Tangential :

7.00%

Radial:

4.50%

Unit Movement Tangential:

Unit Movement Radial:

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:

F22

F22

F17

F14

F11

Seasoned:

F34

F27

F22

F17

F14

Density per Standard

Seasoned:

1050kg/m3

Unseasoned:

1250kg/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:

110

Modulus of Rupture - Seasoned:

140

Modulus of Elasticity - Unseasoned:

16

Modulus of Elasticity - Seasoned:

18

Maximum Crushing Strength - Unseasoned:

51

Maximum Crushing Strength - Seasoned:

72

Impact - Unseasoned:

19

Impact - Seasoned:

21

Toughness - Unseasoned:

Medium - 15 - 24 Nm

Toughness - Seasoned:

Medium - 15 - 24 Nm

Hardness - Unseasoned:

10

Hardness - Seasoned:

14

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:

Not Susceptible

Lyctid Borer Susceptibility - Other:

Termite Resistance:

Resistant

Fire Properties

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

Fire Properties Group
Number:

Group Number - Other:

3 if used on MDF or particleboard ≥12mm; veneer thickness 0.6-0.85mm

Average Specific Extinction Area:

<250

Bushfire Resistance:

BAL 12.5 and 19 – All AS3959 required applications

Decking

Download the WoodSolutions Technical Design Guide on Domestic Timber Decking here.

Timber decks are a practical and attractive addition to any outdoor landscape. Natural timber decks blend seamlessly with their surrounding environment and will serve as popular entertaining areas all year long.

As an external structure, carrying large loads of traffic, timber decking has high structural performance requirements. In addition decks are usually raised clear off the ground and fully exposed to the weather meaning an effective deck must be able to cope with wear and tear from repeated use and in addition discharge rainwater efficiently. Roundin the corners (easing the arris) of the decking will help run off water while spacing for ventilation between the decking boards will prevent water ponding on the deck surface. 

Timber decking is available in both seasoned and unseasoned wood, in a wide range of species, sizes and grades. The natural appeal and strength of timber makes it a practical choice for outdoor decking. This guide provides an overview of best practice methods for specifying, installing and finishing a timber deck.

Retaining Walls (Landscaping)

The natural appeal, strength and versatility of timber makes it an ideal choice for retaining wall landscaping applications.

Retaining wall systems include cantilevered round or sawn timber, mass wall and crib wall construction. Walls up to one metre in height follow a basic design and can usually be constructed using standard proprietary wall systems. An engineer will be required to plan and design walls greater than one metre, including the footings and drainage.

Drainage of retaining walls is a critical factor in influencing the long term stability of the wall and should thus form a significant part of the design and planning process. 

Regular care and maintenance of retaining walls is essential in ensuring the long-term stability and safety of the structure.

Structural Timber Poles

Timber pole construction is typically utilised to provide support for gravity loads and resistance against lateral forces. The natural appeal of timber ensures that its role is not purely structural however, with timber poles complimenting architectural designs aimed at harmonisation with the natural environment. The small number of footings required in pole frame construction also ensures minimal disturbances to the site.

With a double bearer system, poles can be spaced further apart than is usual, creating a more spacious building interior, that allows greater interior design flexibility. While poles are usually placed in a grid like system this is not compulsory and the flexibility of the application means the system can cope with a wide variety of designs, enabling designers to take full advantage of beautiful outlooks.

This article provides a comprehensive overview of the process involved in specifying, designing and constructing a solid timber pole construction.

Flooring

Whether for structural or finished flooring applications, timber offers durability, versatility and adaptability. The warmth, strength and natural beauty of timber flooring has proved enduringly popular in a wide variety of interior settings.

Timber flooring is a timeless product, offering a warmth and natural beauty largely unmatched by other flooring options. This article provides an overview of the installation of solid timber strip flooring over bearers and joists, timber based sheet flooring products and concrete slabs. Timber flooring is typically supplied as either solid timber or laminated wood products, made from layers of bonded timber. It fits together with a tongue and groove joint and once in place, is sanded and finished. There is a wide variety of species to select flooring from and the right species for a given application will be dependent on numerous factors. Information relating to species selection, environmental assessment, finish selection and recommended maintenance routines are all provided in this section.

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