Teak

Teak (Tectona grandis)

Sagwan, Jati, May Sak, Giati, Teck, Kyun

General characteristics:

It reaches a diameter of up to 1.5 m. Heartwood is brownish-gold with possibly darker streaks present. Sapwood clearly distinguished. The teak harvested from it finds a range of uses in construction and interior design. It is distinguished by its high content of oily substances and silicic acid, so it does not soak up water and shows resistance to harmful substances. The medium hardness of the material allows for easier working, while the beautiful colouring and grain gives the finished products a striking appearance.

Origin:

Teak trees naturally occur in southern Asia, such as in: Burma, India, Laos and Thailand, as well as in Indochina, colonising monsoon forests. It is a fast-growing species (only plantation varieties, the natural stands we have on offer do not grow fast). Optimum growth conditions are air temperatures of 22 -27^oC and water abundance associated with heavy rainfall. The rapid growth of teak trees and the great interest in their wood has led to the establishment of plantations of the species in many parts of the world, including Africa and Central America.

Tree habit:

Depending on the habitat, an 80-year-old teak tree can be between 15 and 45 m tall (typical felling age is 40-60 years). It has a shallow root system, 70-80 cm deep, but very extensive, reaching up to 20 m laterally from the base of the trunk.

Structure type:

Ring-shaped (wood from natural monsoon forests) or halfring-vascular (wood from plantation crops); the large vessels of earlywood arranged singly form distinguishable rings; the vessels are visible to the naked eye (0.14 to 0.27 mm in diameter). Latewood vessels, of smaller diameters, are arranged singly or in groupings of two, forming no major structures.

Sapwood:

Narrow (2 to 4 cm wide), whitish-grey in colour.

Heartwood:

In freshly sawn wood, heartwood is coloured greenish. When exposed to light and oxygen in the air, heartwood darkens intensely to a brown colour. Heartwood in tangential and radial sections is usually enriched, running longitudinally, by dark brown or greyish black strands a few millimetres wide

Fragrance:

Long-lasting, similar to the smell of tanned leather.

Pattern:

thanks to the differentiation in the structure of the early and late wood, annual increments is clearly visible on all cross-sections. On cross-section, their undulations and varying widths become apparent. Each grain begins with more or less distinct rings of earlywood vessels. Numerous, rather narrow but relatively high vascular rays can be seen on the radial section and much more difficult so on the transverse section. These are homocellular rays. There are tangential strands of wood parenchyma in earlywood, which are narrower in wood from plantation crops (compared to wood from natural forests). In the latter case, vessels are also found within this parenchyma. In addition, there is poor paratracheal and perivascular parenchyma, which is concentrated mainly in the latewood. Plantation wood is characterised by wider annual increments.

Typical defects:

Uneven saltiness, discolouration, high mineral content and natural oils.

Properties of Teak wood:

According to the six-grade density scale, teak is a moderately heavy wood (grade III and IV). The average density for the air-dry state (for wood with a moisture content of approximately 12%) is 660 kgm-3. Teak wood is characterised by a low fibre saturation point moisture content (22%). The greatest asset of this wood is its low shrinkage values, indicating a particular dimensional stability and lack of tendency to crack and warp. According to Monnin's classification, teak is a low-shrinkage wood. The mechanical properties indicate that it is a hard, flexible and easily flaky species. A distinctly more stable grade with high natural durability against external influences.

Similar species:

In terms of properties, the substitutes for teak wood are Iroko and Afromosia.

Drying:

Does not cause difficulties.

Working:

Teak wood is straight-grained, which makes it easier to process, but its high mineral content (e.g. silicon dioxide) causes tools to dull more quickly. The wood dust from teak, which is produced during cutting, contains irritating substances and therefore causes irritation of the mucous membranes and dermatological problems. The high oil content results in rapid tool dressing and dulling, and the use of forked (carbide) tools is recommended.

Joining:

The oily nature of the wood makes the bonding process difficult. These substances reduce the adhesion of adhesives. To improve the wettability of bonded teak surfaces, they can be wiped with an organic solvent or a 10% sodium hydroxide solution and then neutralised with a 10% acetic acid solution.

Finishing:

It is not very difficult, but the surfaces must be thoroughly cleaned beforehand; oiling gives the best results.

Intended use:

Veneers, furniture, garden furniture, flooring, boatbuilding, fittings.

• Mechanical properties: Working is not difficult, bonding is good, nailing requires pre-drilling.
• Modulus of elasticity: 13.7 GPa
• Tangential shrinkage: 4.7%
• Radial shrinkage: 2.6%
• Specific gravity: 670 kg/m³ (12%)
• Durability: species resistant to destructive fungal attack
• Dry wood pests: resistant – risk limited to sapwood penetration
• Protections: class 4 – non-accepting