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Tasmanian Blue Gum
A tough but pale hardwood, its notable hardness and density make it ideal for floors, fittings and surfaces expected to take considerable wear.
Tasmanian Blue gum is a fine compliment to Tasmanian Oak.
Tasmanian blue gum is pale straw to brown, often with blue to green-grey tones. The sapwood is paler than the heartwood, but often difficult to distinguish. Blue gum is one of Tasmania’s most durable timbers, which, combined with its strength, makes it a good structural timber. In keeping with its density, blue gum has to be seasoned and worked with care.
The timber established a reputation with early European settlers for its toughness and durability, particularly for bridge construction and wharf piling. More recently, its potential as an appearance timber has been recognised. The leaves and large flower cases of the tree have a strong and characteristic fragrance. Oils extracted from blue gum leaves were also exported for use in medicines and varnishes.
Blue Gum grows in wet or dry eucalypt native forests and in plantations from 0-400m. In dry conditions, the tree takes on wide spreading profile, whereas in wet forests it grows tall and straight.
Blue Gum grows rapidly and is easily raised from seed. While it grows up to a metre per year, intense cultivation can double these rates. Blue Gum does not tolerate frost. Its best natural development is in the moist valleys of hilly areas on good quality loams, and likes dolerite and shallow humus soils over mudstone.
Blue Gum grows naturally along the east coast, usually within 20km of the coast, but in some areas up to 60–70km inland. It is also found in the south and west and on some Bass Strait islands.
Blue Gum occurs in dry and wet eucalypt native forest type and 35% of these forest types are reserved. There are currently approximately 23,800ha of Blue Gum in plantations, which is about 10% of Tasmania’s plantations.
The flower of the Blue Gum is Tasmania’s floral emblem and the tree is probably the state’s most recognisable eucalypt. Known to reach 90m in height, it commonly grows to 70m. Fast growing, it can grow more than one metre in height and 12mm in diameter per year.
Buds usually grow alone, though they can grow in groups of three, and are large, warty and covered in a fine powder.
The Blue Gum flowers from September to December. Once open, the buds shed a round cap and display characteristic white flowers before developing into ribbed gum nuts about 25mm across.
The Blue Gum’s juvenile leaves are up to 15cm long, have a red edge, and are covered with a blue-grey waxy bloom. The leaves of older trees are dark green, tough, sickle-shaped and roughly 25cm.
The bark at the base of the tree is rough, red-brown and peels off in ribbons. At the top of the trunk and branches, the tree is smooth with a dappled grey and cream bark.
Tasmanian Blue Gum Technical Details
- Undressed seasoned and unseasoned timber 50 to 150 mm wide by 25 to 50 mm thick. Lengths up to 5400 mm long are available. Flooring profiles available.
- Sometimes straight, sometimes interlocked. Fairly coarse and even with distinct growth rings.
- Uniform and smooth.
- Durability Description
- Termite resistance of heartwood: Not resistant. Refer to AS 5604-2005 Timber - Natural durability ratings.
- In-ground: Class 3
- Above-ground: Class 2
- Movement - Shrinkage
- Approximately 7% radial, 15% tangential before reconditioning; 5% radial and 10% tangential after reconditioning.
- Unseasoned: Approximately 1100 kg/cu m
- Seasoned: Approximately 900 kg/cu m at 12% moisture content.
- Strength Group
- Unseasoned: S3
- Seasoned: SD2
- Joint Group
- Unseasoned: J1
- Seasoned: JD1
- Structural Grades
- Most commonly available stress grades are F22 seasoned, F11 unseasoned.
- Toughness (Izod)
- Unseasoned: 16
- Seasoned: 23
- Hardness (Janka)
- Unseasoned: 7
- Seasoned: 10
Fire Hazard Properties
- Fire hazard Properties: Flooring (AS ISO 9239.1)
- Critial Radiant Heat Flux: 4.5 kW/m2 or greater
- Smoke Development Rate: Less than 750 %-min
- Fire Hazard Properties: Wall and Weiling Lining (AS/NZ 3837)
- Material Group: 3
- Average Extinction Area: Less than 250 m2/kg
- Usually cuts cleaning with high feeding forces.
- High feeding forces required. Machine marks may be difficult to remove.
- Surfaces are true and clean, even end grain. Holds edges exceptionally well.
- Difficult to drill, but holes are usually very clean and to size.
- Rebating + Mortising
- Difficult but produces good results.
- Seasoned material is difficult to nail; pre-drilling is often necessary.
- Exceptional care required when preparing surfaces for gluing. Must be performed under properly controlled conditions with suitable formulations.
- A good bending material.
- Can be worked to smooth, very resilient surface. Most finishes adhere well.
Tasmanian Blue Gum Environmental Details
- Native - Wet Eucalypt and Dry Eucalypt, Plantation.
- 35% of the total Bluegum forest types are reserved.
- Chain of custody
- Carbon storage
- 396 kg/cu m
- R Values
- 0.47 (100mm)
- Blue Gum's availability is limited, and is constrained by location and style of harvesting operations.