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Merawan Wood: Characteristics and Applications

Introduction
Merawan wood refers to the light wood obtained from various species of the Hopea genus (family Dipterocarpaceae). In Malaysia, it is commonly known as "Merawan" with different epithets depending on the region, such as "Luis" and "Mang" in Sarawak, and "Selangan" in Sabah and Sarawak. In Sabah, "Gagil" is specifically used for Hopea sangal. The wood is often mixed with lighter species of Shorea and marketed as Selangan Batu No. 2 in Sabah. Key species of Merawan include Hopea beccariana, H. dryobalanoides, H. dyeri, H. ferruginea, H. glaucescens, H. griffithii, H. latifolia, H. mengarawan, H. montana, H. myrtifolia, H. nervosa, H. odorata, H. pierrei, H. pubescens, H. sangal, H. sublanceolata, and H. sulcata. The sapwood of Merawan is generally lighter in color, with poorly defined boundaries separating it from the heartwood, which is yellow when fresh and darkens to light brown or red-brown upon exposure.

International Names
Merawan wood is also known by various names around the world:
- *Brunei*: Merawan
- *Cambodia*: Koki khsach, Koki:r, Popel, Popel mosau
- *India*: Hopea, Thingan
- *Indonesia*: Dammar mata kuching, Gagil, Merawan
- *Laos*: Khe:n, Mai khaen heua
- *Myanmar*: Thingan
- *Papua New Guinea*: Light Hopea
- *Philippines*: Manggachapui
- *Thailand*: Chan-phu, Takhian-Tong, Takian, Takian Thong
- *Vietnam*: Kien-kien, Sao den

Density
Merawan is classified as a Medium Hardwood, with an air-dry density ranging between 495 and 980 kg/m³.

Natural Durability
Merawan wood is considered moderately durable when used under exposed conditions. It is particularly resistant to fungal infections under normal conditions. However, the sapwood is highly susceptible to termite damage and fungal decay in damp environments.

Preservative Treatment
Merawan wood is difficult to treat with preservatives, making it less ideal for applications where preservation is critical.

Texture and Grain
The wood has a moderately fine and even texture, with an interlocked grain pattern that contributes to its strength and aesthetic appeal.

Strength Properties
Merawan wood falls into Strength Group B (Engku, 1988b) or SG 4 (MS 544:Part 2:2001), making it suitable for various structural and decorative applications.

| Species | Moisture Content (%) | Modulus of Rupture (MPa) | Modulus of Elasticity (MPa) | Impact Bending (mm) | Compression Parallel to Grain (MPa) | Shear Parallel to Grain (MPa) |
| --- | --- | --- | --- | --- | --- | --- |
| H. nervosa | 64 | 92 | 15,500 | 760 | 50.8 | 9.3 |
| H. sulcata | 61 | 90 | 15,000 | 690 | 45.9 | 9.0 |

Machining Properties
Merawan wood is moderately easy to work with in terms of sawing and cross-cutting. Planing is relatively easy, and it typically produces a smooth finish.

| Species | Condition | Sawing | Planing | Boring | Turning |
| --- | --- | --- | --- | --- | --- |
| H. nervosa | Green | Easy | Easy | Smooth | Slightly Difficult |
|  | Air Dry | Moderately Easy | Fairly Easy | Smooth | Smooth |
| H. sulcata | Green | Easy | Easy | Smooth | Easy |
|  | Air Dry | Easy | Easy | Smooth | Smooth |

Nailing Property
The nailing property of Merawan wood is rated as very poor, which may limit its use in certain applications where nailing is essential.

Air Drying
Merawan wood seasons slowly, with slight cupping as the primary defect. Thinner boards (13 mm) take approximately 4 months to air dry, while thicker boards (38 mm) require around 6 months.

Kiln-Drying
Kiln Schedule H is recommended for drying Merawan wood. For example, 25 mm thick boards take around 5 days to kiln-dry from 50% to 10% moisture content without any recorded drying defects.

| Moisture Content (%) | Temperature (Dry Bulb) | Temperature (Wet Bulb) | Relative Humidity (%) |
| --- | --- | --- | --- |
| Green | 135°F (57.0°C) | 127°F (53°C) | 80% |
| 50% | 135°F (57.0°C) | 126°F (52°C) | 75% |
| 40% | 140°F (60.0°C) | 126°F (52°C) | 65% |
| 30% | 150°F (65.5°C) | 129°F (54°C) | 55% |
| 20% | 170°F (76.5°C) | 136°F (58°C) | 40% |

Shrinkage
Merawan wood exhibits average shrinkage, with radial shrinkage in H. sulcata averaging 0.9% and tangential shrinkage averaging 2.2%.

Common Defects
Merawan logs may exhibit hollow or spongy heart, though these defects are less extensive compared to most red merantis. Some species (e.g., H. sulcata, H. myrtifolia, H. dyeri, and H. mengarawan) are highly susceptible to ambrosia beetle damage, while others are resistant. Merawan wood is generally immune to powder-post beetle attacks, though some species are moderately susceptible. The sapwood of all species is prone to sapstain infection.

Applications
Merawan wood is versatile and suitable for various applications, including:
- Rafters, joists, door and window frames, and sills (for internal use)
- Panelling, mouldings, partitioning, and joinery
- Furniture, plywood, flooring, and decking
- Staircase components (angle blocks, rough bracket, baluster, handrail, etc.)
- Columns (light duty) and railway sleepers
- Vehicle bodies (framework, floorboards, and planking)
- Ship and boat building (keels, keelsons, framework, and general planking)
- Cooling tower structural members and tool handles (non-impact)
- Heavy construction under cover for the heavier species