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)

Modulus 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 (%)

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

  1. Burgess, P. F. 1966. Timbers of Sabah. Sabah For. Rec. No. 6.
  2. 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.
  3. Dahlan b. Jantan & Tam, M. K. 1986. Natural Durability of Some Malaysian Timbers by Stake Test. (in press).
  4. 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.
  5. Jackson, W. F. 1965. Durability of Malaysian Timbers. Mal. For. Ser. Trade Leaflet No. 28.
  6. 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.
  7. MS 544:Part 2:2001. Code of Practice for the Structural Use of Timber : Permissible Stress Design of Solid Timber.
  8. 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.