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Gum, Spotted

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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.

 

 

 

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.

 

Common Form

Sawn

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

Availability - Further Information

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.

Availability - Further Information

Native Forest

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

Portal Frames

Timber portal frames are one of the most favoured structural applications for commercial and industrial buildings whose functions necessitate long spans and open interiors. As a material choice, timber offers designers simplicity, speed and economy in fabrication and erection.

Timber portal frames offer a strong, sound and superior structure. Structural action is achieved through rigid connections between column and rafter at the knees, and between the individual rafter members at the ridge. These rigid joints are generally constructed using nailed plywood gussets and on occasion, with steel gussets.

From material selection to finishing, this application guide provides a comprehensive overview of the process of using timber in the specification, fabrication and erection of portal frame structures.

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.

Mouldings

Timber mouldings add style, class and an elegant touch to any interior, offering a depth of beauty and warmth in a way only wood can. From period times to those more contemporary, timber mouldings have graced the most stylish and chic of interiors, decorating furniture, doors and windows. Decorative mouldings such as architraves, skirtings, cornices and ceiling roses remain an ever popular choice for designers seeking a finished result of beauty, style and quality. Like all timber products, mouldings are extremely versatile and durable, enhancing the aesthetics of any interior and functioning as the perfect finishing touch for designs with a focus on beauty and splendour.

Mouldings can be created from any commercially available species of timber and the moisture resistant wood product, MDF, is also a popular choice. When it comes to style and design, the sky is the limit with many suppliers offering custom matching to existing mouldings, as well as efficient supply of those that are individually designed. Installation is a breeze, with the majority of mouldings easily attached with a reputable wood adhesive. Finishes can be tailored by design requirements and the preferences of the end user, with mouldings commonly being both stained and/or painted.

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.

Stairs, Exterior

All exterior stairs serve a functional purpose, but the choice of timber in the application will turn a functional building element into an aesthetically pleasing feature. And while the construction of stairs is demanding, the investment of time will be returned, with a well constructed timber staircase typically lasting decades.

Exterior stairs are usually built from treated softwood and durable hardwoods and typically finished with paint. The construction procedure described here applies to most general type stairs of either conventional or contemporary construction.

When it comes to stairs there is a multitude of variations available for application depending on the structural requirements of the building. This guide discusses the most commonly specified stair types.

Stairs, Interior

Interior staircase work is considered a specialised area of carpentry and joinery as its construction requires high levels of workmanship, detail and accuracy. Many interior stairs are built from quality joinery timber, cut and seasoned especially for staircases. Interior stairs differ considerably in design, from simple straight flights, commonly used in domestic work, to more elaborate stairs, constructed purposely as stand out features in public and commercial buildings.

The construction procedure described here applies to most general type stairs of either conventional or contemporary construction.

Pergolas

Timber pergolas offer an attractive and economical way to create functional living and entertainment areas in the outdoors.  Pergolas designed with care can maximise both winter sunshine and summer shade, ensuring outdoor living is enjoyed all year round. With its natural look, durability and versatility there are few other materials that can match the advantages of timber in pergola construction.

Pergolas are typically constructed via a straightforward post and beam process, which can be attached to an existing building or form a free standing structure. A protective finishing coat will preserve the life of the pergola and a variety of paints and stains are available on the market to facilitate this.

 

Rails and Balustrades, Exterior

The versatility, strength and natural beauty of timber makes it the ideal material choice for external handrails and balustrades. Usually built from treated softwood and durable hardwoods these timbers can be turned to create a range of styles and designs, resulting in balusters that are unique as they are individual. Painting, staining and oil based finishes broadly cover the wide range of finishing options available and with the appropriate care and attention a timber balustrade can last a lifetime.

This guide provides general information on member sizes, connections and suitable materials to enable the construction of a long lasting, attractive and durable timber handrail or balustrade.

Cladding, External

No other cladding material can offer the design freedom, ease of handling, range and natural beauty of timber. Timber cladding can create a building to suit almost any environment, taste or style.

Timber cladding has an inbuilt flexibility that provides natural advantages on sites subject to high winds, extreme climate, highly reactive soils, subsidence or earth tremors. And unlike masonry and other rigid materials, the natural resilience and high strength to weight ratio of timber enables it to withstand far greater stresses and movement.

Modern finishes give a long lasting and attractive appearance to timber cladding and can be used to change the colour and style of the building, making it a versatile material that will keep pace with changing tastes and fashions.

 

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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