Spotted gum is a species that grows well on favourable sites, usually attaining 35-45 m in height and 1-1.3 m diameter at breast height (dbh), with exceptionally large trees reaching 70 m and exceeding 3 m dbh. On poorer sites it may be 20-35 m in height and 0.7-1.2 m diameter. This species naturally occurs in open-forest to tall open-forest formation on the east coast of Australia from the Victoria-New South Wales border to the Maryborough District in Queensland. Trial plantings have been established in the south-west of Western Australia for pole timber.
Heartwood is light brown to dark brown, and sapwood is pale and up to 8 cm wide. The texture is moderately coarse, with an interlocked grain, and the frequent presence of wavy grain produces an attractive ' fiddleback' grain. The wood is slightly greasy and gum veins are common.
Green density is the density of wood in the living tree, defined as green mass divided by green volume, and useful for estimating transport costs. It varies with season and growing conditions.
Air-dry density is the average mass divided by volume at 12 per cent moisture content (this is the average environmental condition in the coastal capital cities around Australia).
Basic density is oven-dry mass divided by green volume. This measure has the advantage that moisture content variations in the tree during the year are avoided.:
Green density is about 1150 kg/m3, the air-dry density about 970 kg/m3, and basic density about 790 kg/m3.
Tangential and radial shrinkage before reconditioning are 6.1 and 4.3 per cent respectively, and after reconditioning 5.0 and 3.7 per cent respectively.
The timber is not difficult to work. Unseasoned wood is somewhat corrosive to aluminium nails and screws, and the high extractives content can be a problem when gluing phenolic-type adhesives. For good bonding a pressure of about 1000 kPa and temperatures above 200 C are usually needed. A low moisture content, preferably between 8 and 10 per cent, is also desirable.
The CSIRO Durability Classes are based on the performance in ground of outer heartwood when exposed to fungal and termite attack.
|1||More than 25|
|2||15 to 25|
|3||8 to 15|
|4||Less than 8|
The ratings are not relevant to above-ground use. In late 1996, CSIRO published revised ratings, which include termite susceptibility. Ratings are now available for about seventy species for decay, and for decay plus termites.:
Durability Class based on the 1996 CSIRO assessment is 2 for decay, and 2 for decay + termites combined. Sapwood is Lyctus-susceptible.
Minimum values (MPa) for strength groups for green and seasoned timber come from Australian Standard AS2878-1986 'Timber - Classification of strength groups'. In grading structural timber, each species is allocated a ranking for green timber of S1 (strongest) to S7, and for seasoned timber SD1 (strongest) to SD8.
MOR is modulus of rupture or bending strength, MOE is modulus of elasticity or 'stiffness', and MCS is maximum crushing strength or compression strength. Hardness refers to the Janka hardness test and is a measure of resistance to indentation.
Minimum values (Mpa) for green timber
Minimum values (Mpa) for green timber
Where test data were available, they are shown in bold print. Most values are from Bootle (1983), Wood in Australia. Types, properties and uses. (McGraw-Hill), or Julius (1906), 'Western Australian timber tests 1906: The physical characteristics of the woods of Western Australia'.
Where no strength data were available, air-dry density was used in accordance with the Australian Standard AS2878-1986 Timber - Classification of strength groups to predict the strength group. Consequently, the strength values quoted are from the above two tables.:
Green and dry strength groups are S2 and SD2 respectively. The more important strength properties are given in the table below.
|Modulus of Rupture||MPa||99||150|
|Modulus of Elasticity||MPa||18000||23000|
|Max Crushing Strength||MPa||50||75|
The timber is not readily available in Western Australia, although common in New South Wales and southern Queensland.
The uses are as heavy engineering construction and mining timbers, where shock resistance is important, house framing, flooring, tool handles, piles and poles, shipbuilding, agricultural machinery and