Wood species
Kapur wood
Kapur is a hardwood (Dryobalanops spp.). At 12% moisture content it has a Janka hardness of 1,230 lbf (5,471 N) and it weighs about 49 lb/ft³ (787 kg/m³), 4.1 lb (1.86 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 1,230 lbf (5,471 N)
- Green: 980 lbf (4,359 N)
- Weight at 12% MC
- 49 lb/ft³ (787 kg/m³)
- 4.1 lb per board foot
- Specific gravity (oven-dry weight)
- 0.64 on green volume
- Shrinkage, green to oven-dry
- 10.2% tangential
- Radial 4.6%, volumetric 14.8%
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; kapur's density is worked from its specific gravity with the Handbook's own equations.
How much kapur moves
A 12 in wide flatsawn board of kapur that goes from 6% to 12% moisture content swells about 0.27 in (about 9/32 in, 6.8 mm). Quartersawn, the same board moves about 0.11 in (about 1/8 in, 2.9 mm). Flatsawn faces move 2.2 times as much as quartersawn ones, because the wood shrinks 10.2% around the growth rings but only 4.6% 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
- Reddish brown heartwood, clearly set off from pale sapwood.
- Grain and texture
- Fairly coarse but uniform; straighter grained than keruing.
- Working and character
- Strength like keruing. Works fairly easily, but silica can blunt cutters badly when dry; dull cutters raise the grain. Resists decay; very hard to treat.
- Uses
- Durable construction lumber and plywood.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-26 to 2-27.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for kapur 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 | 12% MC |
|---|---|---|
| Bending strength (MOR) | 12,800 psi (88 MPa) | 18,300 psi (126 MPa) |
| Stiffness (MOE) | 1,600,000 psi (11 GPa) | 1,880,000 psi (13 GPa) |
| Crushing strength (compression parallel to grain) | 6,220 psi (43 MPa) | 10,090 psi (70 MPa) |
| Shear parallel to grain | 1,170 psi (8 MPa) | 1,990 psi (14 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 1,230 lbf of side hardness at 12% moisture content for kapur, 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 kapur, so it is moved to 12% with the volumetric shrinkage of 14.8% (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 49 lb/ft³, or 4.1 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources