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Mahogany, White

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White mahogany is one of Australia's premium native hardwoods with a high degree of natural durability and strength, making it an ideal timber for a variety of structural, exterior and interior applications.

White mahogany is the common name for four species that grow along the east coast of Australia, from mid-New South Wales to northern Queensland, with isolated pockets north of the Queensland tablelands. Sawn timbers from these species are readily available across Australia.

They have straight, slender trunks with rough, fibrous bark that is shed in strips, giving the trees their characteristic stringy appearance and resulting in the common local names of yellow or white stringybark.

The species varies in appearance but not in durability class or other properties. The heartwood is light brown to yellow brown in colour. The sapwood is usually creamy brown and is uniformly lighter than the heartwood. White mahogany wood has a slightly greasy feel, a characteristic that aids machining and boring.

It is termite resistant and the sapwood can be easily treated with preservatives. The heartwood is too dense to accept readily available commercial preservation processes.

The wood is used as a sawn timber 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. White mahogany is also used in the manufacture of veneer and plywood. Other applications include boatbuilding, coach and carriage building, and agricultural machinery.

Appearance

White mahogany timbers are available in a narrow range of colours. The heartwood is light brown to yellow brown in colour and has a similar appearance to tallowwood. The sapwood is usually creamy brown, clearly lighter in colour than the heartwood and generally less than 20mm wide.

A mostly uniform and medium textured wood, white mahogany can sometimes have an interlocked grain. It can also feature distinctive markings caused by moth grub holes and occasional gum veining. It has a slightly greasy feel, although not as greasy as the similarly coloured tallowwood or spotted gum.

Common Applications

White mahogany is often used for above ground framing and decking in both protected and unprotected contexts. It can also be used for heavy construction work, from sawn and round timber in wharf and bridge construction to railway sleepers, cross arms, poles, piles. and as mining timbers. It is employed in general house framing, as cladding, linings, joinery, fencing, landscaping and in retaining walls. The species is also suitable for use in structural plywood, boat building (keel and framing components, planking), coach, vehicle and carriage building and agricultural machinery. It is often used in internal and external flooring as its hardness means it does not easily dent, and is also frequently used in outdoor furniture due to its durability.

Common Form

Sawn

Workability

White mahogany machines well due to its natural greasiness, and there is no difficulty using it with standard fittings and fastenings. Due to its hardness, the timber is not easily worked with hand tools. As with other high-density species, machining and surface preparation should be done immediately before gluing. Easily painted, stained, and polished, the sapwood readily accepts preservatives but the density of the hardwood makes it resistant to current commercial preservative compounds.

Origin of Timber

NSW

Readily Available

NSW

Availability - Further Information

White mahogany is an important commercial species in NSW and Queensland.

Availability - Further Information

Native Forest

Shrinkage

Very Low Low Medium High Very High

Tangential :

5.40%

Radial:

2.80%

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:

F27

F17

F14

F11

F8

Seasoned:

F27

F22

F17

F14

F11

Density per Standard

Seasoned:

950kg/m3

Unseasoned:

1150kg/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:

101

Modulus of Rupture - Seasoned:

130

Modulus of Elasticity - Unseasoned:

16

Modulus of Elasticity - Seasoned:

17

Maximum Crushing Strength - Unseasoned:

49

Maximum Crushing Strength - Seasoned:

76

Impact - Unseasoned:

17

Impact - Seasoned:

14

Toughness - Unseasoned:

Medium - 15 - 24 Nm

Toughness - Seasoned:

Medium - 15 - 24 Nm

Hardness - Unseasoned:

8.9

Hardness - Seasoned:

10

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

0 1 2 3 4 5 6 7 8 9 10

EFH Spread-of-Flame Index:

EFH Smoke-Developed Index:

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

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.

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.

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.

 

Shear walls

Framed timber buildings, of post and beam or stud and joist construction, resist lateral loads (wind, earthquake or impact) by using rigid frames (portals), braced frames (trusses and cross-bracing) or structural sheathing elements (diaphragms).

Diaphragms are an efficient structural solution to resist lateral forces. The sheeting materials that are generally used as lining or cladding can usually be upgraded to resist shear loads, easily and economically. The framing then performs dual functions, resisting both horizontal and vertical loads.

In cases where diaphragms comprise structural sheathing, additional design efficiencies can be incorporated to resist loads normal to walls, floor and roofs using the composite stressed skin action developed between the sheathing and the timber frame.

The advantages of timber shear walls and diaphragms include:

  • architectural design freedom (curves, cantilevers, clear spans) 
  • lightweight construction 
  • high impact load resistance 
  • resilience (no brittle cracks) 
  • fast conventional construction 

In this section you'll find information about the design and construction details of timber framed diaphragms (both horizontal and vertical) used in domestic, low rise commercial and industrial buildings.

Framing design for dead loads, or dead and live loads acting normal to the framing are covered in AS 1720.1 Timber Structures and AS 1684 Residential timber-framed construction. To develop efficient diaphragm action, some adjustments, particularly connection details, are usually required.

Information about diaphragm materials and systems is included, however the majority of the design and construction details provided herein are for structural plywood diaphragms for which documented design information is available.

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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