Wood species
Merbau wood
Merbau is a hardwood (Intsia spp.). At 15% moisture content it has a Janka hardness of 1,500 lbf (6,672 N) and it weighs about 47 lb/ft³ (752 kg/m³), 3.9 lb (1.77 kg) per board foot.
Also called: ipil, kwila.
Key numbers
- Janka hardness, 15% MC
- 1,500 lbf (6,672 N)
- Green: 1,380 lbf (6,139 N)
- Weight at 12% MC
- 47 lb/ft³ (752 kg/m³)
- 3.9 lb per board foot
- Specific gravity (oven-dry weight)
- 0.64 on green volume
- Shrinkage, green to oven-dry
- 4.6% tangential
- Radial 2.7%, volumetric 7.8%
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4)
Why: From the USDA Wood Handbook, which collected these values from the world literature; merbau's density is worked from its specific gravity with the Handbook's own equations.
How much merbau moves
A 12 in wide flatsawn board of merbau that goes from 6% to 12% moisture content swells about 0.11 in (about 1/8 in, 2.9 mm). Quartersawn, the same board moves about 0.07 in (about 1/16 in, 1.7 mm). Flatsawn faces move 1.7 times as much as quartersawn ones, because the wood shrinks 4.6% around the growth rings but only 2.7% across them.
Worked from the Wood Handbook's shrinkage values (Table 4-4) with its Eq. 13-4; the Handbook gives no movement coefficients for imported woods. Individual boards vary: the Handbook gives shrinkage a coefficient of variation of about 15% (p. 4-11).
Color, grain and working
- Color
- Yellowish to orange-brown fresh, turning brown or dark red-brown.
- Grain and texture
- Rather coarse texture; grain straight to interlocked or wavy.
- Working and character
- Strength comparable with hickory at a lower density. Dries well, but stains black with iron and moisture; sticks to saw teeth and dulls edges, yet dresses smooth and finishes well. Durable and termite resistant.
- Uses
- Furniture, joinery, turnery, cabinets, flooring and musical instruments.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-31.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for merbau from Wood Handbook Table 5-5b (p. 5-23), which the Handbook says were collected from the world literature, on clear, straight-grained specimens. Knots and cross grain make lumber weaker than these clear samples (Handbook Chapter 5).
| Property | Green | 15% MC |
|---|---|---|
| Bending strength (MOR) | 12,900 psi (89 MPa) | 16,800 psi (116 MPa) |
| Stiffness (MOE) | 2,020,000 psi (13.9 GPa) | 2,230,000 psi (15.4 GPa) |
| Crushing strength (compression parallel to grain) | 6,770 psi (47 MPa) | 8,440 psi (58 MPa) |
| Shear parallel to grain | 1,560 psi (11 MPa) | 1,810 psi (12 MPa) |
A dash means the Handbook prints no value; none is filled in.
Dust and health
- Wood dust is classed as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer, chiefly for cancers of the nose and sinuses.
- NIOSH recommends keeping wood dust exposure to 1 mg/m³ of total dust, as quoted in OSHA's sawmill guidance.
This is what the named authorities publish, not medical advice.
Compare with
Why these numbers
Why these numbers?
The situation
The Wood Handbook prints 1,500 lbf of side hardness at 15% moisture content for merbau, a value it says was collected from the world literature (Table 5-5b, p. 5-23).
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4) , sources [1]
What that means
Side hardness (Janka) is the load needed to press a 0.444 in (11.28 mm) steel ball halfway into the wood across the grain; a higher number dents less (Handbook p. 5-5).
One source: USDA Forest Products Laboratory, collected from the world literature (its Tables 5-5 and 4-4) , sources [1]
So
The Handbook gives only the green specific gravity (0.64) for merbau, so it is moved to 12% with the volumetric shrinkage of 7.8% (Eqs. 4-9 and 4-11), then multiplied by water's density and 1.12 (Eq. 4-14).
Arithmetic: exact by definition , sources [1]
The number
About 47 lb/ft³, or 3.9 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources