Black bean

Scientific name

Castanospermum australe. Family: Leguminosae

Local names

Moreton Bay bean, Moreton Bay chestnut, beantree

Description and natural occurrence

A tall tree up to 40 m in height with a stem diameter to 1.2 m. The trunk is not prominently buttressed. The crown is very dense, consisting of abundant dark green glossy foliage. The large pendant bean-like fruit are conspicuous in the crown. The bark is slightly rough with very small pustules and is coloured grey to brown.

This species is scattered in rainforest regions from Lismore, New South Wales to Iron Range on Cape York Peninsula. It is also found in New Caledonia and Vanuatu.

Wood appearance

Colour. The heartwood ranges from dark brown to chocolate shades deepening almost to black; sometimes streaked with lighter coloured bands. The sapwood is white to yellow in colour.

Grain. Porous and coarse grained, with striated vessel lines prominent on longitudinal surfaces. This effect is due to chalky grey soft tissue (parenchyma) surrounding the vessels.

Wood properties

Density. 755 kg/m3 at 12% moisture content; approximately 1.3 m3 of seasoned sawn timber per tonne.

Strength groups. S4 unseasoned; (SD5) seasoned.

Stress grades. F7, F8, F11, F14 (unseasoned), F8, F11, F14, F17 (seasoned), when visually stress graded in accordance with AS 2082:2000, Timber - hardwood -visually stress-graded for structural purposes.

Joint groups. J3 unseasoned; JD2 seasoned.

Shrinkage to 12% MC. 5.8% (tangential); 1.8% (radial).

Unit shrinkage. 0.40% (tangential); 0.16% (radial). These values apply to timber reconditioned after seasoning.

Durability above-ground. Class 1 - life expectancy over 40 years.

Durability in-ground. Class 1 - life expectancy over 25 years.

Lyctine susceptibility. Untreated sapwood susceptible to lyctine borer attack.

Termite resistance. Not resistant.

Preservation. Sapwood readily accepts preservative impregnation but penetration of heartwood is negligible using currently available commercial processes.

Seasoning. Care is needed in seasoning this species as it shrinks irregularly and is prone to collapse.

Hardness. Moderately hard (rated 3 on a 6 class scale) in relation to indentation and ease of working with hand tools.

Machining. Machines and turns well to a smooth finish. The dry dust can cause nose and throat irritation to some people.

Fixing. No difficulty has been experienced with the use of standard fittings and fastenings.

Gluing. Can be satisfactorily bonded using standard procedures.

Finishing. Staining is normally not necessary. It polishes well but because of the coarse texture, prior filling may be necessary.

Uses

Engineering. Once used as sawn and round timber in bridge construction and as mining timbers.

Construction. Once had limited use in general house framing and more commonly as flooring, lining, mouldings and joinery, but is rarely used for these applications now.

Decorative. Plywood, furniture, shop and office fixtures, joinery, turnery, carving, inlay work, walking sticks, umbrella sticks.

Others. Gunstocks, knife handles, vehicle and carriage building. It was popular for timber split fence posts during the early days of settlement in rainforest areas of the Atherton Tableland, where durable, easily split timbers were scarce.

Identification features

General characteristics

Sapwood. White to yellow, distinct from heartwood.

Heartwood. Dark brown to chocolate, sometimes with fine white streaks from vessel contents or more diffuse streaks due to soft tissue surrounding vessels.

Texture. Coarse, with some figure.

Wood structure

Growth rings. Absent.

Vessels. Medium to large, in radial rows but with some solitary. Chalky white deposits in some vessels.

Parenchyma. Abundant, aliform with some confluent.

Rays. Visible without a lens.

Other features

Burning splinter test. A match size splinter produces a full white to buff coloured ash.

Figure. Prominent figure caused mainly by the parenchyma associated with vessels.

Further reading

Boland, DJ, Brooker, MIH, Chippendale, GM, Hall, N, Hyland, BPM, Johnston, RD, Kleinig, DA and Turner, JD 2006, 'Forest trees of Australia', 5th edn, CSIRO Publishing, Collingwood Australia.

Bootle, K 2005, 'Wood in Australia: types, properties and uses', 2nd edn, McGraw-Hill, Sydney.

Hopewell, G (ed.) 2006, 'Construction timbers in Queensland: properties and specifications for satisfactory performance of construction timbers in Queensland, Class 1 and Class 10 buildings', books 1 and 2, Department of Primary Industries and Fisheries, Brisbane.

Ilic, J 1991, 'CSIRO atlas of hardwoods', Crawford House Press, Bathurst, Australia.

Standards Australia, 2000, 'AS 2082-2000: Timber - hardwood - visually stress-graded for structural purposes', Standards Australia.

Last updated 28 July 2010