Resak Wood: Properties and Applications

Introduction
Resak wood is sourced from Cotylelobium spp. and Vatica spp. and is commonly known as resak in Malaysia. The heartwood varies from pale yellow to deep red-brown, with species-specific grain patterns. Resak is known for its strength, durability, and versatility in heavy-duty applications.

Key Characteristics

• Density: A Heavy Hardwood with a density ranging from 655-1,155 kg/m³ (air dry).

• Durability: Classified as very durable, lasting over 14 years under natural Malaysian conditions. Not resistant to marine borers but moderately durable against other conditions.

• Strength: Falls under Strength Group B (SG4), making it suitable for heavy construction and high-impact applications.

• Machining: Resak can be challenging to saw and cross-cut but generally yields a smooth finish when planed.

Applications

Resak is ideal for:

• Heavy Construction: Used in bridges, beams, and piling.

• Marine Construction: Suitable for fender supports and other marine uses.

• Flooring: Especially for areas with heavy traffic.

• Furniture: Its strength and fine grain make it ideal for high-end, heavy-duty furniture.

• Railway Sleepers & Poles: Suitable for railway sleepers and power transmission poles.

Handling and Drying

• Air Drying: Seasons slowly, requiring approximately 3 to 5 months to air dry without significant defects.

• Shrinkage: Resak has high shrinkage, particularly in the tangential direction.

• Kiln-Drying: Recommended Kiln Schedule B for controlled drying to avoid surface-checking.

Conclusion
Resak wood stands out for its heavy-duty applications, durability, and strength. Its versatility and longevity make it a preferred material for construction, marine, and industrial uses.

INTRODUCTION

The Standard Malaysian Name for the tree and timber of Cotylelobium spp. and Vatica spp. (Dipterocarpaceae). Vernacular names applied include resak (Peninsular Malaysia, Sabah and Sarawak) with various epithets, balau (Peninsular Malaysia) in error, damar keluang (Pahang), jenuong (Johor) and keruing babi (Peninsular Malaysia). Major species include Cotylelobium lanceolatum, C. melanoxylon; Vatica bella, V. cuspidata, V. flavida, V. havilandii, V. heteroptera, V. lowii, V. maingayi, V. mangachapoi, V. nitens and V. scortechinii. The sapwood is lighter in colour than the heartwood and is sharply defined in Cotylelobium but not generally so in Vatica. The heartwood is pale yellow when fresh and turns to deep red-brown on exposure in Cotylelobium and a fine brown with a green tinge in Vatica.

Also known as Resak (Brunei); Chrama:hs (Cambodia); Vatica (India); Giam, Resak and Resak bukit (Indonesia); Chik dong, Mai ka cha, Mai si and Mai si khao (Laos); Vatica (Papua New Guinea); Narig (Philippines); and Chan Thip, Dam Darng, Khian, Khiem, Kiam, Pan-Cham, See, Tamsao and Yang-nu (Thailand).

  
DENSITY

The timber is a Heavy Hardwood with a density of 655-1,155 kg/m3 air dry. 

NATURAL DURABILITY

Graveyard tests on V. cuspidata, a species with an average air dry density of 1,040 kg/m3 indicated that the timber has an average service life of 14 years under natural conditions. The timber is therefore, classified as very durable under Malaysian conditions (Jackson, 1965). Desch (1941) recorded that tests carried out to determine the quality of resak timber indicated that some forms of resak were found to be exceptionally durable (presumably the heavier varieties), ranking with the best forms of balau and giam, and the inferior forms (presumably the lighter varieties) would appear to be at least moderately durable. Burkill (1935) stated that the timber of Cotylelobium is of excellent quality and resistant to Teredo, a type of marine borer. Burgess (1966) however, reported that the timber of Vatica species is not resistant to marine borers and failed within 12 months in Papua New Guinea. In general, resak should not be accepted as resistant to marine borers, but material of Cotylelobium, since it contains silica, is likely to be more resistant than Vatica.

PRESERVATIVE TREATMENT

Generally, preservative treatment is not necessary for Malaysian Heavy Hardwoods including the timber of resak. The timber was quoted as very difficult to treat (Lee and Chu, 1974). In general, the heartwood of the hard and heavy forms of resak are expected to be as difficult to treat as other Malaysian Heavy Hardwoods, e.g. balau, chengal and bitis. It is therefore, unlikely that resak will absorb preservatives of any worthwhile quantity except possibly for the sapwood of the lighter species.

TEXTURE

Texture is fine and even, with straight or only shallowly interlocked grain.

STRENGTH PROPERTIES

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

Strength Properties of Resak

MACHINING PROPERTIES

It is difficult to resaw and cross-cut in Vatica, while Cotylelobium is moderately easy to slightly difficult to resaw. Planing is easy to slightly difficult and the finished surface is smooth. 

Machining Properties of Resak

AIR DRYING

The timber seasons fairly slowly with very negligible degrade. Only slight cupping, end-checking, splitting and surface-checking are noted during drying. 13 mm thick boards take approximately 3 months to air dry, while 38 mm thick boards take 5 months.

KILN-DRYING

Kiln Schedule B is recommended. Resak, which is hard and heavy as chengal (Neobalanocarpus heimii), needs very slow drying as it is extremely prone to surface-checking. In order to minimise the drying costs and defects, the timber should be air dried to below 30% moisture content before kiln-drying.

Kiln Schedule B  

SHRINKAGE

Shrinkage is high, especially in the tangential direction. Radial shrinkage averages 1.5% while tangential shrinkage averages 3.4%.

DEFECTS

The timber is generally free from any major defects except in some logs, which may contain some heart shakes and some accompanying decay. Compression failure is occasionally present in some logs. No �pin� or �shot� hole borer attack in the heartwood has been observed but the sapwood is liable to powder-post beetle attacks. Surface-checking of the timber is common but not severe. Some resin pockets may be present.

USES

The timber is suitable for all forms of heavy construction, bridges, piling, marine construction, beams, posts, joists, pallets (permanent heavy duty), door and window frames and sills, tool handles (impact), flooring (heavy traffic), power transmission poles, laboratory benches, vehicle bodies (framework and floor boards), railway sleepers, fender supports, staircase (angle blocks, rough brackets, carriage, riser, stringer, tread, bullnose, round end and winder), cooling tower (structural members), telegraphic and power transmission posts and cross arms, heavy duty furniture and wooden containers.