Australian Standard Specs:

Technical data sugar gum (Eucalyptus cladocalyx) on durability and shrinkage

Class 1 durability both in and above ground
Refer to Standards Australia: Timber - Natural durability ratings AS 5604-2005. This standard completely replaces all previous durability ratings and classifications and is the cumulation of decades of long-term in-ground testing and research by CSIRO and other organisations. Visit the Standards Australia website to purchase in either hard copy or pdf format. ISBN 0-7337-6751-6. Key features in summary are:

Above ground
Sugar gum untreated heartwood for above ground applications such as decking has a probable life expectancy of more than 40 years. This rating is the highest available under the Australian Standard and without stating the obvious MORE than 40 years untreated is a long time. This outstanding feature will also minimise the maintenance costs as it does not require CCA, oiling, painting, sealing or other treatments to achieve this rating. For aesthetic reasons, sugar gum can be coated, stained or left to grey naturally.

In ground
Sugar gum untreated heartwood for in ground applications such as posts has a probable life expectancy of more than 25 years. This rating is also the highest available under the Australian Standard.

As a comparison to other species plantation sugar gum is, after decades of long term in ground and above ground field testing and research, superior to the following species:

• Silvertop ash - in ground only 5-15 years;
• River red gum - in ground only 15-25 years;
• Red stringybark - in ground 15-25 years;
• Spotted gum - in ground 15-25 years;
• Jarrah - in ground 15-25 years.

Additionally sugar gum is supplied from mature plantations, aged 40-110 years. Others of the above species are found only in native forests in mature form. The same holds true for all of sugar gum's only other naturally durable competitors such as ironbark and tallowwood. Most native hardwood plantations are less than 10 years old, and therefore unsuitable for sawlog production.

Shrinkage is similar to other native hardwood species

Shrinkage of sugar gum has been recently reviewed by CSIRO and compared with the previous timber shrinkage study conducted in 1961. The key finding is that sugar gum, while having a higher density, performs within the range for other native timbers with which industry already works. Sugar gum has a (green) density kg m3 of 1119.

Specifically 27 year old plantation sugar gum has tangential shrinkage of 8.5% and radial shrinkage of 3.4% (from green to 12% MC). Mature sugar gum has a tangential shrinkage of 10.5% and a radial shrinkage of 6.2% (from green to 12% MC). Mature sugar gum has similar but slightly higher shrinkage values to alpine ash yet sugar gum although it is more than 60% more dense than ash.

Plantation sugar gum has been used as fence post in western Victoria for decades and is performing well. Plantation sugar gum in service is reliable, sound, highly durable and in terms of shrinkage performs on par with most 'traditional' native forest timbers.

Foresters' journal Australian Forestry (Vol.67, No.3 pp. 152-55) concludes in an article on 'Wood properties of plantation-grown eucaplypts:

"The comparison with E. delegatensis [mountain ash - high rainfall species] shows that while the four low rainfall plantation eucalypts [including sugar gum] have high densities, shrinkage problems should not be significantly worse than those which industry already copes with through design considerations.

"While the high densities may cause some initial problems with sawing, machining and gluing, these should be readily resolvable. The advantages of these timbers should be their high strength and durability properties, possibly making them suited to applications such as outdoor furniture decking and flooring, as well as interior furniture and flooring."

It should be noted that the other three low rainfall species tested were yellow gum, brown mallet and swamp yate, none of which has as high a durability rating as sugar gum.