GERUTU
INTRODUCTION
The Standard Malaysian Name for the timber of the heavier species of Parashorea (Dipterocarpaceae). Vernacular names applied include gerutu (Peninsular Malaysia) with various epithets, heavy white seraya (Sabah), meranti gerutu (Peninsular Malaysia) and other localised names which are too numerous to be listed here. Major species include P. densiflora, P. globosa and P. stellata from Peninsular Malaysia, and P. parvifolia and P. smythiesii from Sabah and Sarawak. The sapwood is whitish yellow and is moderately distinct from the heartwood, which is light golden brown and darkens to a deep brown on exposure.
Also known as Mai hao, Mai nao and Mai si (Laos); Kaunghmu, Tavoy wood and Thingadu (Myanmar); Khai Kheio and Kian-suai (Thailand); and Cho chi (Vietnam).
DENSITY
The timber is a Light Hardwood with a density of 640-880 kg/m3 air dry.
NATURAL DURABILITY
From the standard graveyard test of untreated P. stellata carried out at the Forest Research Institute Malaysia (FRIM) based on test sticks of dimension 50 mm x 50 mm x 600 mm, it was observed that 60% of the test sticks were destroyed within the first year. Subsequently, in the second and third year, 70% and 90% of the test sticks were destroyed respectively. All the test sticks were destroyed in the fifth year of service (Jackson, 1965). Under such circumstances, gerutu is classified as not durable. In a later series of test, Dahlan & Tam (1986, in press) also reported that P. stellata gave an average service life of 1.9 years, thus confirming the results obtained by Jackson (1965). However, treated specimens of P. stellata gave an average service life of about 14 to 17.2 years, and about 14 years for P. densiflora.
PRESERVATIVE TREATMENT
The timber is difficult to treat with preservatives.
TEXTURE
Texture is moderately coarse and even, with interlocked grain.
STRENGTH PROPERTIES
The timber falls into Strength Group C (Engku, 1988b) or SG 5 (MS 544:Part 2:2001).
| Strength Properties of Gerutu | ||||||
|---|---|---|---|---|---|---|
| Species | Test Condition | Modulus of Elasticity(MPa) | MModulus of Rupture(MPa) | Compression parallel to grain (MPa) | Compression perpendicular to grain (MPa) | Shear strength (MPa) |
| P. densiflora | Green | 19,700 | 94 | 50.5 | 7.0 | 8.4 |
| P. stellata | Green | 13,200 | 74 | 41.5 | 4.3 | 7.9 |
MACHINING PROPERTIES
It is slightly difficult to saw but is fairly easy to cross-cut. Planing, boring and turning are easy and the planed surface is smooth.
| Sawing And Woodworking Properties of Gerutu | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Species | Test Condition | Sawing | Planing | Boring | Turning | ||||
| Re-sawing | Cross Cutting | Ease of planing | Quality of finish | Ease of boring | Quality of finish | Ease of turning | Quality of finish | ||
| P. densiflora | Green | slightly difficult | fairly easy | easy | smooth | easy | fairly smooth | - | - |
| Air dry | slightly difficult | fairly easy | easy | smooth | easy | fairly smooth | easy | moderately smooth | |
| P. stellata | Green | slightly difficult | easy | easy | tangential smooth, radial rough | easy | smooth | - | - |
| Air dry | slightly difficult | moderately easy | easy | moderately smooth | easy | fairly smooth | moderately easy | moderately smooth | |
NAILING PROPERTY
The nailing property is rated as excellent.
AIR DRYING
The timber seasons slowly with moderate end-checking and surface-checking and staining as the main sources of degrade. There are also slight splitting and insect attack during drying. 13 mm thick boards take 4 months to air dry, while 38 mm thick boards take about 6 months.
KILN-DRYING
Kiln Schedule C is recommended.
| Kiln Schedule C | |||||
|---|---|---|---|---|---|
| Moisture Content (%) | Temperature (Dry Bulb) | Temperature (Wet Bulb) | Relative Humidity (%) (approx.) | ||
| °F | °C | °F | °C | ||
| Green | 105 | 40.5 | 101 | 38.0 | 85 |
| 60 | 105 | 40.5 | 99 | 37.0 | 80 |
| 40 | 110 | 43.5 | 102 | 39.0 | 75 |
| 35 | 110 | 43.5 | 100 | 38.0 | 70 |
| 30 | 115 | 46.0 | 103 | 39.5 | 65 |
| 25 | 125 | 51.5 | 109 | 43.0 | 60 |
| 20 | 140 | 60.0 | 118 | 47.5 | 50 |
| 15 | 150 | 65.5 | 121 | 49.0 | 40 |
SHRINKAGE
Shrinkage is high, with radial shrinkage averaging 1.8% and tangential shrinkage averaging 3.5%.
MOVEMENT IN SERVICE
The movement of seasoned timber is classified under Type IV (based on the species P. densiflora).
DEFECTS
Brittle-heart is normally present and may be appreciable in some logs. Burgess (1966) recorded that, in general, brittle-heart in this timber did not extend for more than 175 mm to 200 mm from the pith. Timber affected by brittle-heart is susceptible to compression failures and liable to break up into small pieces. Knots are small and infrequent. Shot-hole borer attack occasionally occurs in the living tree and is rarely serious, but the pin-hole borer attack in felled logs may cause severe damage. Defects other than those mentioned above are quite negligible.
USES
Light to medium construction under cover, panelling, mouldings, partitioning, flooring, staircase (apron lining, handrails, sprandrel framings and risers), joinery, cabinet making, furniture, railway sleepers, plywood, pallets (expendable type), packing boxes and crates as well as tool handles (non-impact purpose).
REFERENCES
- Burgess, P. F. 1966. Timbers of Sabah. Sabah For. Rec. No. 6.
- Choo, K. T. & Lim, S. C. 1986. Malaysian Timbers - Gerutu. Timber Trade Leaflet No. 101. The Malaysian Timber Industry Board and Forest Research Institute Malaysia, Kuala Lumpur. 8 pp.
- Dahlan b. Jantan & Tam, M. K. 1986. Natural Durability of Some Malaysian Timbers by Stake Test. (in press).
- Engku Abdul Rahman Chik. 1988b. Basic and Grade Stresses for Strength Groups of Malaysian Timbers. Malayan Forest Service Trade Leaflet No. 38. The Malaysian Timber Industry Board and Forest Research Institute Malaysia, Kuala Lumpur.13 pp.
- Jackson, W. F. 1965. Durability of Malaysian Timbers. Mal. For. Ser. Trade Leaflet No. 28.
- Menon, P. K. B. 1986. Uses of Some Malaysian Timbers. Revised by Lim, S. C. Timber Trade Leaflet No. 31. The Malaysian Timber Industry Board and Forest Research Institute Malaysia, Kuala Lumpur. 48 pp.
- MS 544:Part 2:2001. Code of Practice for the Structural Use of Timber : Permissible Stress Design of Solid Timber.
- Wong, T. M. 1982. A Dictionary of Malaysian Timbers. Revised by Lim, S. C. & Chung, R. C. K. Malayan Forest Records No. 30 Forest Research Institute Malaysia, Kuala Lumpur. 201 pp.