Northern silky oak

Scientific name Cardwellia sublimis. Family: Proteaceae.
Local names

Oak, bull oak, silky oak.

Description and natural occurrence

A large tree commonly attaining 40 m in height and 2 m in stem diameter. The trunk, usually without buttresses, is normally straight. The bark is slightly flaky to non-descript. The outer blaze is commonly biscuit-brown in colour.

This species has a limited distribution in North Queensland between Mt Spec, near Townsville, and Bloomfield.

Wood appearance

Colour. The heartwood is pale pink to brown. Sapwood is usually almost white.

Grain. Moderately coarse textured and variable. Quarter sawn timber shows the decorative oak grain to best effect.

Wood properties

Density. 560 kg/m3 at 12% moisture content; approximately 1.8 m3 of seasoned sawn timber per tonne.

Strength groups. S6 unseasoned; SD7 seasoned.

Stress grades. F4, F5, F7, F8 (unseasoned), F5, F7, F8, F11 (seasoned), when visually stress graded in accordance with AS 2082: 2000, Timber - hardwood - visually stress-graded for structural purposes.

Joint groups. J4 unseasoned; JD4 seasoned.

Shrinkage to 12% MC. 4.7% (tangential); 1.6% (radial).

Unit shrinkage. 0.31% (tangential); 0.13% (radial). These values apply to timber reconditioned after seasoning.

Durability above-ground. Class 4 - life expectancy less than 7 years.

Durability in-ground. Class 4 - life expectancy less than 5 years.

Lyctine susceptibility. Untreated sapwood susceptible to lyctid borer attack.

Termite resistance. Not resistant.

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

Seasoning. Can be satisfactorily dried using conventional air and kiln seasoning methods.

Hardness. Soft (rated 5 on a 6 class scale)in relation to indentation and ease of working with hand tools.

Machining. Machines and turns well to a smooth surface.

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

Gluing. Can be satisfactorily bonded using standard procedures.

Finishing. Will readily accept paint, stain and polish. Because of the open grain in this species, filling may be required before the timber is polished.

Uses

Construction. Once used extensively in North Queensland in general house framing, cladding, lining, moulding, joinery (particularly windows) and flooring. Now confined more to joinery applications.

Decorative. Plywood, furniture, outdoor furnishings, joinery, shop and office fittings, turnery, carving, inlay work.

Others. Has been used for boat building (light), brushware, gunstocks, cooperage, vehicle and coach building.

Identification features

General characteristics

Sapwood. Creamy white in colour.

Heartwood. Pink to pinkish-brown in colour.

Texture. Coarse and irregular, a broad ray figure on quarter-sawn surfaces, grain straight.

Wood structure

Growth rings. Indistinct.

Vessels. Large, numerous, solitary or in short tangential hoops between the rays. Tyloses absent, but occasionally vessels are filled with whitish deposits or deposits of red coloured gum.

Parenchyma. Abundant, aliform and confluent, including vessels between rays, forming loops, generally concave outwards; an occasional short tangential apotracheal band.

Rays. Of two distinct kinds (a) broad to very broad, plainly visible without a lens on all surfaces, and (b) fine, indistinct even under hand lens.

Other features

Burning splinter test. A match size splinter burns to charcoal.

Splinter shape. Fine needle-like splinters produced when cutting across the grain are characteristic of this species and can be used to separate northern silky oak from similar species.

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 02 September 2010