The Blue Gum group is suitable for tongue and groove flooring, in-sequence parquet, overlay, joinery stairs, doors, furniture, paneling, decking, outdoor furniture, and sliced veneer. The Stringybark group is suitable for flooring, joinery, decking, cross arms (mainly E. microcorys), and sliced veneer. The Ash group is suitable for furniture, joinery, and sliced veneer.
Sustainability of supply
New Zealand has 28575 hectares planted in eucalypts, with a median age less than 10 years. Approximately 7.5% is of millable age.
Eucalypts are exceptionally fast-growing, with timber grown in New Zealand to 30 years age similar to much older material from Australia.
Most of the harvestable timber available at present is located in the Central North Island, although small quantities are also becoming available in Northland and Auckland regions.
Significant plantings of young Eucalypt trees have been made in the past 5 years in the Otago and Southland regions, and also the Central North Island.
The eucalypt species have common names in Australia but are known by their botanical names in New Zealand.
This avoids confusion over the type of eucalypt being referred to, due to the extremely large variety of eucalypt species.
Confusion can remain, however, when imported timber classifications are used when marketing timber from Australia.
It is therefore recommended to request the botanical name of the species from any timber supplier, or else to request information regarding the mechanical properties and durability class of the timber being sold.
The eucalypt species grown in New Zealand are grouped as follows for simplicity because of their similarities:
The Eastern Blue Gum group: E saligna and E. botryoides
The Stringybark group: E. muelleriana, E. globoidea, E. eugenoides, E. microcorys, E. pilularis.
The Ash group: E. delegatensis, E. fastigata, E. regnans, E. obliqua.
Botanical name: Eucalyptus spp
Other common names: Eucalypts
Strength: Eucalypt timber has good strength properties.
Durability: The heartwood of all the blue gum and stringybark species are durable in ground contact, lasting 15 to 25 years in ground contact and up to 40 years out of ground contact, giving an equivalent durability of H3.2. The ash group species are only moderately durable, lasting 5 to 15 years in ground contact giving an equivalent durability of H3.1.
Finishes: The dry timber finishes well, and takes all types of stains and paints. The higher density species may be difficult to glue, e.g. E. muelleriana.
Working properties: Difficulties with eucalypts relate mainly to the sawing of logs, where growth stresses may be a problem, and with drying, as some species are collapse-prone.
Appearance: The heartwood of the blue gums, E. saligna and E. botryoides is dark pink to reddish brown with a paler sapwood. The heartwood of the stringybark group species is yellowish-brown with a pink tinge, and the sapwood paler. The heartwood of E. fastigata is predominantly pale brown with occasional purplish flecks. E. obliqua looks very like European oak. The heartwood of E. regnans and E. delegatensis is pale pink or light brown that is sometimes difficult to differentiate from the pale sapwood. It has a moderate-coarse texture and straight grain.
- Eucalypt timber has several appealing characteristics. It is strong, dense, offers attractive colour choices, and the timber of some species has natural durability.
These wood properties differ between species, although species with similar attributes are often treated as one product line.
New Zealand-grown timber is less dense than Australian-grown timber, but has similar properties to mature Australian stands, although being considerably younger when cut (usually around age 30).
The Blue Gums
The heartwood of E. Saligna and E. Botryoides is dark pink to reddish brown with a paler sapwood. The wood has a fairly coarse, even texture with an interlocked grain. Gum veins are common.
The heartwood of the stringybark group species is yellowish-brown with a pink tinge, and the sapwood paler. The wood has a fine-medium and even texture, and the grain is often interlocked.
Stringybarks are characterised by high density, good durability, excellent sawing characteristics, and high strength.
Stringybarks have been used for a wide range of suitable end uses, included non-submerged wharf decking, cross-arms, sports arena and dance hall flooring, in-ground posts, durable half rounds for landscaping, as well as high quality furniture.
E nitens, though a blue gum, also has these excellent high strength and hardness properties of the group.
The Ash group
The Ash timbers were planted primarily as a replacement for tawa as a pulping timber, with the lower sawlogs available for solid wood utilisation.
The heartwood of E. fastigata is predominantly pale brown with occasional purplish flecks. It has a medium and even texture, and grain can range from interlocked to straight.
The heartwood of E. regnans is pale pink or light brown that is sometimes difficult to differentiate from the pale sapwood. It has a moderate-coarse texture and straight grain.
The Ash group has best appearance when quartersawn, with a ribbon-like mahogany-type appearance.
Durability class 1 Durability class 2 Durability class 3 Durability class 4 Description Very durable Durable Moderately durable Non-durabale Hazard class H4 H3.2 H3.1 H1.2 Life expectancy in ground(yrs) >25 15 - 25 5 - 15 0 - 5 Life expectancy above ground(yrs) >40 15 - 40 7 - 15 0 - 7 Botryoides Delegatensis ** Gunnii Globoidea Globulus * Microcorys Obliqua# Muelleriana Regnans# Pilularis Fastigata#~ Saligna
* upper end of range #lower end of range ~provisional, based on incomplete tests
The correspondence between durability class and hazard class is made assuming that structural members will be larger than the 50x50mm stakes used to establish durability class and that timbers used out of ground contact will be provided with some kind of surface coating or are used in a non-horizontal application where water quickly drains off.
In use as decking, which is horizontal and uncoated, the service life is 15 rather than 50 years because it is easily replaced and not a serious safety concern.
Eucalypt heartwood cannot be treated with waterborne preservatives. The heartwood of all the blue gum and stringybark species are durable in ground contact, lasting 15 to 25 years in ground contact and up to 40 years out of ground contact.
The ash group species are only moderately durable, lasting 5 to 15 years in ground contact.
The Summary Fact sheet .pdf contains the mechanical properties for the Eucalypt species.
The Ash group have a ‘brittle heart’ in the core of the timber of lower density timber, and contains shakes.
The mechanical properties are very similar to native tawa.
The strength combined with hardness properties mean they are an excellent timber for furniture and turnery.
The Blue Gums and Stringybarks offer little difficulty in sawing and drying, but E. delegatensis can be more difficult to dry and process.
It is recommended that quartersawn timber be milled and used for the Ash group timbers, but flatsawn timber is not likely to give trouble from stringybarks and E. saligna.
Eucalyptus species make excellent veneer, and can be peeled from a very young age, due to the fast growth rate and tall tree heights achievable.
As well as decorative overlays, specialist plywood and LVL can also be produced from Eucalyptus veneers. This exhibits very high strength and stiffness properties.
Difficulties with eucalypts relate mainly to the sawing of logs, where growth stresses may be a problem, and with drying, as some species are collapse-prone.
The dry timber finishes well, and takes all types of stains and paints. The higher density species may be difficult to glue, e.g. E. muelleriana.
Eucalypts can be used for the following applications:
Blue gum group
- Flooring – tongue and groove
- in-sequence parquet
- outdoor furniture
- sliced veneer
- cross arms (mainly E. microcorys)
- sliced veneer
- sliced veneer
- Case Study
Example of Eucalyptus Muelleriana (yellow stringybark) used for flooring.