Iroko

Iroko (Milicia excelsa)
Kambala, Odum

Origin:

Iroko trees are found in the tropical forests of western, central and eastern Africa. They grow particularly well in humid coastal regions, on fertile clay soils rich in water.

Tree habit:

Under optimum growth conditions, they reach a height of 45 m and a trunk butt diameter of more than 2.5 m (record specimens are up to 50 m high and 3 m in diameter). Also, the Latin name excelsa, meaning tall, emphasises their exceptional size. The trunks of these trees are usually straight, cylindrical in shape, and up to a height of 25 m are devoid of branches.

Structure type:

Diffuse-vascular, vessels with large diameters (0.15 to 0.31 mm), usually found singly or in clusters (2-3 each). There are an average of 1 to 10 vessels per 1 mm² of cross-section (average 3).

Sapwood:

Between 5 and 7.5 cm wide and white-yellow in colour.

Heartwood:

with a distinctive light-yellow colour. A lemon colour is typical for freshly sawn wood. Over time, when exposed to the air, the surface of the wood gradually darkens. Oxidation processes and the associated colour changes are greatly accelerated by light, especially direct sunlight. Iroko wood subjected to prolonged exposure to the aforementioned factors takes on a colour ranging from yellowish brown to dark brown. The intensity of the colour change is also influenced by the chemical composition of the wood, which is partly dependent on the habitat in which the trees grew.

Fragrance:

No characteristic odour.

Pattern:

Iroko wood has a so-called striped fibre twist, which can be observed on the radial cross-section. On cross-section, the vessels are visible as numerous, evenly spaced spots in the vicinity of the paratracheal parenchyma. It usually occurs as winged or winged-streaked, occasionally as annular. On longitudinal sections, the vessels are visible as thin, bright, vertical or oblique lines. The multilayered vascular rays can be clearly seen on the radial section as a fine shiner; on the tangential section they appear as a fine "porridge", on the transverse section macroscopically they are not visible. These are heterogeneous rays. There are also distinguishable annual increments boundaries in Iroko wood harvested from regions with more visible seasons.

Typical defects:

Fibre twist, intense colour change possible.

Properties of Iroko wood:

According to a six-grade scale, it is a heavy wood (grade III). The average density in the air-dry state (wood with a moisture content of approximately 12%) is 690 kg m³. Irok wood has low tensile and shear strength and inferior elasticity due to the striped twist of the fibres. The advantage of this wood is its considerable compressive strength.

Similar species:

Black locust, dibetou, tatajuba, afromosia, teak.

Drying:

Difficult and slow. Iroko wood is prone to cracking and warping, which is related to the presence of a striped twist in the fibres and an extended woody parenchyma.

Working:

The presence of calcium carbonate crystals requires the use of hard tools, preferably with carbide tips and a reduced rake angle. Working with such tools produces good quality surfaces. In addition, the treatment is hindered by the content of non-structural substances, including chlorophorin, which causes irritation to the upper respiratory tract, eyes and skin. Particularly dangerous is the chlorophorin contained in the "airborne" dust generated during working.

Joining:

This wood holds nails and screws well and can also be joined using adhesives.

Finishing:

A properly prepared surface accepts paint and varnish well.

Intended use:

Boatbuilding, shipbuilding, veneers, furniture, floors, doors, interior fittings, high quality joinery products.

Availability
26 mm – KD – LS block-cut – FAS grade
28 mm – KD – SE edged – FAS grade
35 mm – KD – LS block-cut – FAS grade
52 mm – KD – SE edged – FAS grade
76 mm – KD – LS block-cut – FAS grade

• Mechanical properties: It is well workable, but tends to dull tools, especially when limestone structures are present. Nailing and bonding are described as good.
• Modulus of elasticity: 13 GPa
• Tangential shrinkage: 5.4%
• Radial shrinkage: 3.5%
• Specific gravity: 640 kg/m³ (12%)
• Durability: species resistant to destructive fungal attack
• Dry wood pests: resistant – risk limited to sapwood penetration
• Protections: class 4 – non-accepting
• Additionally: naturally resistant to outdoor conditions; can be used outdoors without any protection