Wenge

Wenge (Millettia laurentii)

Palissandre du Congo, Dikela

Origin:

Okoume trees grow in western equatorial Africa. Sites of this plant are found primarily in western and central Gabon and in much smaller areas in neighbouring countries such as: Cameroon, Congo, Equatorial Guinea. The preferred communities are mainly inland rainforests, where up to 40-50 trees can grow per hectare. Okoume are also found in gallery forests and savannahs.

Tree habit:

Okoume trees produce straight, cylindrical, highly branched trunks with board-like flutes, reaching 3 m in height. At felling age (about 50 years), the plant is about 25 m tall and has a diameter at the butt (not counting flutes) of 80-90 cm. The largest specimens can be 35-40 m tall, or even 60 m, with a diameter at the butt of over 2 m.

Structure type:

Diffuse-vascular, the vessels are evenly distributed, either singly or in radial clusters. The diameter of the vessels ranges from 0.07 to 0.57 mm.

Sapwood:

Narrow (2 to 5 cm wide), whitish-yellow in colour.

Heartwood:

In freshly sawn wood, it is more brown in colour. When exposed to light and oxygen in the air, heartwood darkens intensely to a dark brown or even black colour, which is not a uniform pastel colour (the zones of compact fibres are dark, the parenchyma strands are clearly lighter).     

Fragrance:

Freshly sawn wood gives off a characteristic earthy smell that quickly disappears.

Pattern:

The wood clearly shows alternating lighter and darker rings on the cross-section and stripes on the longitudinal sections. These are broad light strands of streaked parenchyma separated by layers of dark, thick-walled fibres. The parenchyma strands are surrounded by vessels whose lumen in heartwood zone is often filled with a dark brown secretion. In cross-section and tangentially, these strands form broad "ribbons". Annual increments are only distinguishable microscopically. It is most often a straight-fibred wood. Fine, 2-4 series, uniform medullary rays are faintly visible. The structural elements form a stratified structure, which is best observed on a tangential section.  

Typical defects:

Insect pavements, mineral inclusions.

Properties of Okoume wood:

According to a six-grade density scale, wenge is a very heavy wood (grade I). The timber in question is characterised by low fibre saturation point moisture content (around 22%) and average shrinkage values. According to Monnin's classification, wenge belongs to the medium-shrinkage wood. The anisotropy of shrinkage is relatively low – less than 1.7. The high density of the wood is associated with good mechanical properties, especially as it is a straight-fibred wood. The average compressive strength is about 85 MPa, the static crushing strength is about 144 MPa and the modulus of elasticity is as high as 18.2 Gpa.  

Similar species:

Some species from Asia, for example Meranti in the genus Shorea sp. or Bintangor in the genus Calophyllum.

Drying:

Easy, as Okoume wood is not prone to cracking or warping (natural drying and seasoning is fast).   

Working:

Hand and machine working is easy. Once dry, the wood planes and sands very well. The resin contained in the phloem can cause allergic and dermatological complaints, which is why personal protective equipment is recommended, especially when sawing roundwood. The wood is excellent at cutting and peeling.  

Joining:

The wood is more difficult to bonding; two-component polyurethane or epoxy-polyurethane adhesives are recommended. When connecting with screws and nails, pre-drilling is required. 

Finishing:

A properly prepared surface accepts paints and varnishes well, but not all paint types are recommended. Although wenge also has considerable acid resistance, acid-curing lacquer hardeners can cause undesirable colour changes.

Intended use:

Staircases, furniture, veneers, flooring, woodwork, musical instruments.

Availability

26 mm – KD – SE edged – FAS grade

52 mm – KD – SE edged – FAS grade

• Mechanical properties: Wood good to work with, but hard to polish. Bonding good, nailing requires pre-drilling. It has good compressive strength and high impact strength
• Modulus of elasticity: 21.0 GPa
• Tangential shrinkage: 9.1%
• Radial shrinkage: 5.9%
• Specific gravity: 880 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: resistant to contact with soil, fresh water or high humidity, naturally resistant to external conditions