Rengas Wood: Features and Applications

 

Introduction
Rengas wood, derived from Gluta spp. and Melanochyla spp., is known for its striking dark red-brown or deep blood-red heartwood with black streaks. It is a prized cabinet wood in Malaysia, commonly referred to as rengas with various epithets across the region.

Key Characteristics

• Density: Medium Hardwood with a density of 640-960 kg/m³ (air-dry).

• Durability: Moderately durable, susceptible to termite attacks.

• Texture: Moderately coarse to fine, with interlocked grain.

• Strength: Classified in Strength Group B (SG4)—strong and suitable for medium construction.

• Machining: Slightly difficult to work with; surfaces can be moderately smooth to rough depending on the process.

Applications

Rengas wood is ideal for:

• Cabinetry and Furniture: Valued for its unique red streaks and rich color.

• Decorative Uses: Suitable for panelling, mouldings, and picture frames.

• Structural Uses: Can be used for beams, posts, rafters, and railway sleepers.

• Ornamental: Great for tool handles, walking sticks, and ornamental pieces.

Note: While the sap is poisonous in fresh timber, seasoned wood is safe to handle.

Handling and Drying

• Nailing: Excellent nailing properties.

• Air Drying: Moderate drying time—13mm boards dry in 2 months, 38mm boards in 5 months.

• Shrinkage: Low shrinkage, making it stable for use.

INTRODUCTION

The Standard Malaysian Name for the timber of Gluta spp. and Melanochyla spp. (Anacardiaceae). Vernacular names applied are usually rengas (Peninsular Malaysia, Sabah and Sarawak) with various epithets. The major species contributing to the timber include Gluta aptera, G. elegans, G. malayana, G. renghas, G. torquata, G. wallichii, G. wrayi; Melanochyla auriculata, M. bracteata, M. caesia and M. fulvinervis. The sapwood is light pink-brown or light brown and is sharply differentiated from the heartwood, which is dark red-brown or deep blood-red, with bands of darker, almost black streaks.

Also known as Rengas (Brunei); Kroeul (Cambodia); Gluta (India); Anga, Poei and Rengas (Indonesia); Mai nam kiang (Laos); Burma Gluta, Chay, Thayet-thitsi and Thitsi (Myanmar); Hekakoro (Papua New Guinea); Lingas (Philippines); and Rak and Rak-ban (Thailand).

DENSITY

The timber is a Medium Hardwood with a density of 640-960 kg/m3 air dry.

NATURAL DURABILITY

The timber is moderately durable, being susceptible to termite attacks.

PRESERVATIVE TREATMENT

The heartwood is extremely difficult to treat with preservatives, while the sapwood is amenable.

TEXTURE

Texture is moderately coarse to fairly fine and even, with interlocked or occasionally straight grain.

STRENGTH PROPERTIES

The timber falls into Strength Group B (Engku, 1988b) or SG4 (MS 544: Part 2: 2001).

Strength Properties of Rengas (G. torquata)

Test Condition	Modulus of Elasticity(MPa)	Modulus of Rupture(MPa)	Compression parallel to grain (MPa)	Compression perpendicular to grain (MPa)	Shear Strength (MPa)
Green	14,000	81	41.4	5.31	10.6
Air dry	14,900	111	59.4	7.65	13.2

MACHINING PROPERTIES

It is slightly difficult to resaw and cross cut and the planed surface is only moderately smooth.

Machining Properties of Rengas (G. torquata)

Test condition	Sawing		Planing		Boring		Turning
	Rip-sawing	Cross- cutting	Ease of planing	Quality of finish	Ease of boring	Quality of finish	Ease of turning	Quality of finish
Green	easy to slightly difficult	easy	easy	moderately smooth	slightly difficult	slightly rough	–	–
Air dry	slightly difficult	slightly difficult	difficult	moderately smooth	slightly difficult	slightly rough	slightly difficult	rough

NAILING PROPERTY

The nailing property is rated as excellent.

AIR DRYING

The timber seasons moderately slowly, with slight twisting and insect attacks as the main sources of degrade. 13 mm thick boards take approximately 2 months to air dry, while 38 mm thick boards take 5 months.

KILN-DRYING

Kiln Schedule E is recommended.

Kiln Schedule E

Moisture Content (%)	Temperature (Dry Bulb)		Temperature (Wet Bulb)		Relative Humidity (%)
	� F	� C	� F	� C
Green	120	48.5	115	46.0	85
60	120	48.5	113	45.0	80
40	125	51.5	116	46.5	75
30	130	54.5	117	47.0	65
25	140	60.0	120	49.0	55
20	155	68.0	127	53.0	45
15	170	76.5	136	58.0	40

SHRINKAGE

Shrinkage is fairly low, radial shrinkage averages 1.0% while tangential shrinkage averages 1.8%.

DEFECTS

The logs of rengas are generally free from defects except for few heart shakes.

USES

Due to the poisonous nature of the sap, the timber is not very often exploited. The seasoned timber, however, is quite safe to handle and is highly prized as a cabinet wood due to its streaky figure and blood-red colour. The timber is also suitable for decorative works, panelling, mouldings, superior joinery, picture frames, flooring, plywood, furniture, railway sleepers, posts, beams, joists, rafters, pallets (permanent light duty), door and window frames and sills (internal use), tool handles (impact), ornamental items and walking sticks. The timber is strong enough for medium construction provided it is protected from termites.