Wood species
Jarrah wood
Jarrah is a hardwood (Eucalyptus marginata). At 12% moisture content it has a Janka hardness of 1,910 lbf (8,496 N) and it weighs about 53 lb/ft³ (845 kg/m³), 4.4 lb (1.99 kg) per board foot.
Key numbers
- Janka hardness, 12% MC
- 1,910 lbf (8,496 N)
- Green: 1,290 lbf (5,738 N)
- Weight at 12% MC
- 53 lb/ft³ (845 kg/m³)
- 4.4 lb per board foot
- Specific gravity (oven-dry weight)
- 0.67 on green volume
- Shrinkage, green to oven-dry
- 11.0% tangential
- Radial 7.7%, volumetric 18.7%
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; jarrah's density is worked from its specific gravity with the Handbook's own equations.
How much jarrah moves
A 12 in wide flatsawn board of jarrah that goes from 6% to 12% moisture content swells about 0.29 in (about 9/32 in, 7.4 mm). Quartersawn, the same board moves about 0.2 in (about 3/16 in, 5 mm). Flatsawn faces move 1.4 times as much as quartersawn ones, because the wood shrinks 11.0% around the growth rings but only 7.7% 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
- Uniform pink to dark red, deepening to brownish red with age.
- Grain and texture
- Even, moderately coarse texture; grain often interlocked or wavy, with gum veins.
- Working and character
- Heavy, hard and strong; very durable and termite resistant. Hard to work because of its density and irregular grain.
- Uses
- Pier and bridge decking, piles and fenders; wear-resistant flooring, though it can splinter under heavy traffic.
Adapted in our own words from the Wood Handbook, Chapter 2, p. 2-26.
Strength
Bending strength is the modulus of rupture (MOR); stiffness is the modulus of elasticity (MOE). Values for jarrah 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) | 9,900 psi (68 MPa) | 16,200 psi (112 MPa) |
| Stiffness (MOE) | 1,480,000 psi (10.2 GPa) | 1,880,000 psi (13 GPa) |
| Crushing strength (compression parallel to grain) | 5,190 psi (36 MPa) | 8,870 psi (61 MPa) |
| Shear parallel to grain | 1,320 psi (9 MPa) | 2,130 psi (15 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 1,910 lbf of side hardness at 12% moisture content for jarrah, 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 (0.67) for jarrah, so it is moved to 12% with the volumetric shrinkage of 18.7% (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 53 lb/ft³, or 4.4 lb per board foot (1/12 ft³), at 12% moisture content.
Arithmetic: exact by definition
Sources