Jak Wood in Sri Lanka: Properties, Traditional Uses, and Modern Applications

Jak as a Timber Species

The jak tree (Artocarpus heterophyllus) is best known in Sri Lanka for its fruit — the world's largest tree-borne fruit — but it also produces timber that has been valued for construction, furniture, and musical instruments for centuries. The heartwood of mature jak trees is a striking golden-yellow colour, highly distinctive, and darkens to a rich amber-orange with age and light exposure.

Jak belongs to the Moraceae family and is related to breadfruit and mulberry. It is a medium to large tree that grows throughout Sri Lanka's wet and intermediate zones, including as a garden and homestead tree. Timber is sourced from felled trees at the end of their productive life, from roadside clearances, and from plantation thinnings — though jak is not grown in managed timber plantations.

Physical Properties

Jak heartwood has a density of approximately 560–640 kg/m³ — comparable to rubberwood — with a generally straight to slightly interlocked grain and a moderate, uniform texture. The distinctive feature of jak timber is its colour: the heartwood ranges from bright yellow in freshly cut timber to deep amber after several years of exposure. The sapwood is pale and clearly distinct from the heartwood.

Jak is moderately hard with good impact resistance. It works well with hand tools and machines adequately with sharp tooling, though the grain can be slightly woolly if tools are not kept sharp. It polishes well and accepts oil and wax finishes that complement its natural colour, though it is less receptive to paint finishes than rubberwood due to its colour bleed-through.

• Density: 560–640 kg/m³
• Colour: golden-yellow to amber-orange heartwood — highly distinctive
• Natural durability: moderate to good — better than rubberwood without treatment
• Workability: good with sharp tools — slightly woolly grain requires attention
• Finishes: oil and wax finishes ideal; paint not recommended due to colour bleed

Natural Durability and Treatment

Jak heartwood has moderate to good natural durability — significantly better than rubberwood and comparable to mahogany for above-ground, interior applications. The sapwood is far less durable and should be excluded from structural applications or treated with VPI.

In traditional Sri Lankan construction, jak was used without treatment — and many jak-framed structures have survived for decades or centuries in reasonable condition. However, in the modern context where buildings are expected to last 50–100 years with minimal maintenance, and where termite pressure is significant, VPI treatment of jak structural timber adds a meaningful and inexpensive margin of protection.

Traditional and Modern Applications

Traditionally, jak was one of the primary materials for Sri Lankan domestic furniture — beds, cupboards, and chests made from solid jak are found in historic homes throughout the wet zone. The wood's distinctive colour and moderate hardness made it well-suited to hand-tool furniture making.

In modern applications, jak is most appropriate for bespoke furniture where its distinctive colour and local provenance are valued, for small architectural elements such as decorative screens and feature panels, and for flooring in heritage restoration projects where matching historic material is important. It is less suited to volume production furniture because of supply inconsistency.

Jak wood is also used in the manufacture of musical instruments — particularly drums — where its tone properties are valued. The jak wood drum (yak bera) is a traditional Sri Lankan instrument, and this application continues to be an important use for high-quality jak timber.

Supply and Sourcing

Jak timber supply in Sri Lanka is informal and inconsistent compared to imported species. There are no managed jak plantations, and most timber comes from individual trees felled in gardens, on roadsides, or from small sawyers who process trees opportunistically. This means that dimensions, drying status, and treatment are rarely standardised.

Buyers of jak timber should verify the moisture content at purchase, confirm whether any drying has been done, and arrange kiln drying and treatment before use in any finished application. Buying jak "off the tree" or from a small sawyer and using it green is the source of most jak furniture failures — the distinctive colour and character of the species does not compensate for timber that moves significantly after manufacture.