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Brown mallet

Eucalyptus astringens

Brown mallet is a small to medium-sized tree, 10-25 m in height and with diameter at breast height (dbh) to 0.7 m, occasionally up to 30 m tall and diameter 1 m. Found in south-west Western Australia on the drier, inland side of the jarrah (E. marginata) forest, in the 300 to 400 mm rainfall zone. It occurs from north-west of York to Narrogin and Wagin, south to GMT Barker and east to near Kondinin, Lake Grace and Ravensthorpe. About 8000 ha of plantations were established near Narrogin.

Wood descriptionThis description can include heartwood and sapwood colour, grain, figure.

Heartwood is light red-brown to dark grey-brown, with reddish streaks, and the sapwood is up to 30 mm wide and distinctly paler.

Wood density

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 1120 kg/m3, air-dry density about 980 kg/m3, and basic density about 770 kg/m3 (published figures). In comparison, CALM Timber Technology measured 1130 kg/m3, 1090 kg/m3 and 865 kg/m3 for the three densities.

Drying and shrinkageAs wood dries, it shrinks more in the tangential direction (i.e. parallel to the growth rings) than it does in the radial direction (i.e. at right angles to the growth rings). The figures given are shrinkage from green to 12 per cent moisture content, before steam reconditioning treatment, and with some species after stream reconditioning. Reconditioning is essential for recovering collapse which may have occurred during the drying process, and is essential for species such as the ash-type eucalypts of eastern Australia.

Tangential and radial shrinkage before reconditioning are 7.1 and 5.5 per cent respectively, and after reconditioning 4.4 and 3.6 per cent respectively.

WorkabilityWith south-west and plantation-grown trees, comments are made on the comparative ease or difficulty of turning, nailing and bending, on susceptibility to splitting and other working properties. With semi-arid, arid and desert species, a more complex survey was made and reported in Siemon and Kealley (1999). The properties assessed were turning, machinability, boring, screwholding, stability, sanding, gluing and finishing. A semi-quantitative score was used: very poor = 1, poor = 2, average = 3, good = 4, and excellent = 5. This book uses the descriptive terms rather than numbers.

With workability, the timber is rather hard to work but dresses well. The grain is often interlocked and the timber is easy to dry.

Durability

The CSIRO Durability Classes are based on the performance in ground of outer heartwood when exposed to fungal and termite attack.

ClassLife Years
1More than 25
215 to 25
38 to 15
4Less 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.

The Durability Class based on the CSIRO 1996 ratings is 2/1 for <decay, and 2 for decay + termites.

Strength group and properties

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

Strength Property S1 S2 S3 S4 S5 S6 S7
MOR 103 86 73 62 52 43 36
MOE 16300 14200 12400 10700 9100 7900 6900
MCS 52 43 36 31 26 22 18

Minimum values (Mpa) for green timber

Strength Property SD1 SD2 SD3 SD4 SD5 SD6 SD7 SD8
MOR 150 130 110 94 78 65 55 45
MOE 21500 18500 16000 14000 12500 10500 9100 7900
MCS 80 70 61 54 47 41 36 30

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 S1 and SD2. The more important strength properties are given in the table below.

Property Units Green Dry
Modulus of Rupture MPa 113 179
Modulus of Elasticity MPa 15000 19000
Max Crushing Strength MPa 53 94
Hardness KN 9.9 15
AvailabilityTimber from many species is available only in limited quantities, from near the areas where the trees grow naturally (or in plantations). There are other species such as red tingle and yellow tingle whose timber is rarely commercially available because the areas of occurrence are predominantly in conservation areas. Other species such as Goldfields timbers are only available in limited quantities because of their scattered occurrence and the fact that the industry is in the early stages of development.

There is limited availability in Western Australia, and timber is generally marketed around the Narrogin area.

UsesVarious past and potential uses are given as a general guide, but the list is obviously not conclusive. In particular, there is increasing interest in specialty timbers, and the semi-arid, arid and desert area species have considerable potential for this use.

Uses have been for general construction (particularly on farms), tool handles, mining timbers and fuel. The bark has high tannin content (40 per cent or more), and this could be used for tanning leather and for adhesives manufacture.