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By Deepak Kumar · Founder, Vriksai

SE Asia and Pacific

Merbau

Intsia bijuga

Also known as kwila, ipil, Moluccan ironwood · Botanical Intsia bijuga

Last updated: 15 July 2026Reviewed by: Vriksai editorial team — timber trade professionalsEditorial policy

Revision history

17 July 2026 — Data re-verified in site-wide audit (formulas, sources, durability classes)
15 July 2026 — Working properties and comparable-species data cross-checked against listed sources

🪵Hardwood🌧Outdoor💧Moisture Stable

Janka Hardness

1712WD

lbf

Janka (metric)

7615calc

Hardness Class

Hardcalc

Density

0.74fpl

g/cm³

MOE

15.4fpl

GPa

MOR

116.0FPL

MPa

Durability

Class 1

Very Durable

Fire (E84)

Class B

indicative

Thermal k

0.198

W/m·K

Green MC

55FPL

Fiber Saturation

26FPL

Radial Shrink

2.7WD

Tangential Shrink

4.6WD

T/R Ratio

1.70derived

Stability

Goodcalc

About the fire rating. Indicative only, derived from density and published data — not a certified rating. Real performance depends on product, thickness, coating and installation. What our ratings do and do not certify.

Compare this wood:⚖ vs Balau ⚖ vs Indian Rosewood ⚖ vs Shisham Sissoo All comparisons →

About Merbau

Merbau (Intsia bijuga) is a hard, wear-resistant timber that is heavy going on tools, with a Janka hardness of 1,712 lbf (7,615 N) and a density of about 0.74 g/cm³. It grows in Southeast Asia and the Pacific.

At 2.7% radial and 4.6% tangential the T/R ratio is 1.70 — typical, and manageable in exterior joinery and cladding provided the gaps are designed rather than assumed. Its fibre saturation point is near 26%. Below it movement is modest at 4.6% tangential, but the 1.70 T/R ratio means one-sided sealing will still pull a panel out of flat.

At 740 kg/m³ a cubic metre of Merbau weighs about 740 kg air-dry — that figure, the 4.6% tangential and 2.7% radial movement and the 1,712 lbf hardness are the three inputs the calculators below actually consume. Select Merbau in any of them to get species-specific results for weight, moisture, shrinkage and hardness.

Working properties

How Merbau behaves at the bench and on the machine, drawn from the CIRAD Tropix database and the ITTO tropical-timber service.

MachiningHard and dense, with a fair-to-difficult response in sawing — the natural deposits gum up and blunt teeth, so carbide is advisable. In planing interlocked quartersawn stock, dropping the cutting angle to about 20° helps prevent grain pick-up. Boring, by contrast, is easy.

FasteningAlways pre-drill for nails and screws — nailing behaviour is otherwise poor and the dense wood splits. Once bored, it holds screws securely.

GluingGlues well for a dense tropical hardwood, though its oil content means surfaces should be clean and freshly prepared.

FinishingTurns, stains, varnishes and paints well and polishes to an even, naturally glossy surface; its high oil content means little upkeep beyond occasional re-oiling.

Steam bendingTolerable steam-bending performance — adequate for gentle curves.

DryingA real strength: it seasons well by kiln or air with little degrade and very little shrinkage or movement, making it notably stable in service.

Durability & use classification

Merbau is rated very durable (EN 350 Class 1), highly resistant to rot, termites and insect attack — hence its long service outdoors. One caution: it holds high tannins and yellow mineral deposits that bleed a reddish-brown stain onto adjacent light surfaces when wet (strongest in the first 6–12 months), so seal it and allow for run-off.

Typical applications & suitability

Indoor Outdoor — Comfortable indoors and out. Its stability and Class 1 durability make it a favourite for decks and exterior joinery, while the same traits suit it to hard-wearing interior floors.

Documented end-uses: interior flooring and exterior decking, outdoor furniture, pergolas and patios, window framing, boat building, carpentry and joinery, heavy structural frameworks and industrial flooring, and boardwalks and bridges.

Comparable species

Species closest to Merbau by density, hardness, stiffness and bending strength, computed directly from the Vriksai species dataset rather than hand-picked.

Garapa720 kg/m³ · 1650 lbf European Beech680 kg/m³ · 1450 lbf Jarrah820 kg/m³ · 1910 lbf Sal740 kg/m³ · 1340 lbf

Trade alternatives. Common decking alternatives are Ipe and Cumaru (denser and even more durable), or regional hardwoods such as Balau and Jarrah. Source merbau from certified stock, as many Intsia populations are under pressure.

Alternatives to Merbau

Merbau measures 1,712 lbf Janka at 0.74 g/cm³, EN 350 durability Class 1, movement rated Good. Because Merbau is exterior-rated at Class 1, every candidate below is too. A substitute that quietly drops a durability class is the expensive kind of mistake. Read the numbers against the Janka scale and EN 350 durability classes.

Step up — harder than Merbau

For exterior joinery, cladding and garden work that also has to resist knocks. Harder means more dent resistance but heavier sections and more machining time.

Jarrah1,910 lbf · 0.82 g/cm³ · Class 1+12% Janka · 0.82 g/cm³ · more stable (Excellent)Wenge1,930 lbf · 0.80 g/cm³ · Class 1+13% Janka · 0.80 g/cm³ · more stable (Excellent)Indian Rosewood2,440 lbf · 0.75 g/cm³ · Class 1+43% Janka

Step down — softer than Merbau

Easier to work and lighter to fix, without dropping below the exterior durability you already have.

Neem1,460 lbf · 0.68 g/cm³ · Class 2-15% Janka Sal1,340 lbf · 0.74 g/cm³ · Class 2-22% Janka ThermoWood Ash Thermo-D1,320 lbf · 0.66 g/cm³ · Class 2-23% Janka · 0.66 g/cm³ · modified timber

Similar, but more dimensionally stable

Cladding boards and exterior joinery live or die on movement. These give you less of it at equal or better durability. Size the gaps with the shrinkage predictor and EMC calculator.

Iroko1,260 lbf · 0.55 g/cm³ · Class 1rated Excellent vs Good · T/R ratio 1.36 vs 1.70 — less cupping tendency · 3.8% tangential movement vs 4.6%ThermoWood Birch Thermo-D1,210 lbf · 0.62 g/cm³ · Class 2stability gained by modification, not by species · 1.6% radial movement vs 2.7% · 3.0% tangential movement vs 4.6%ThermoWood Ash Thermo-D1,320 lbf · 0.66 g/cm³ · Class 2stability gained by modification, not by species · 1.7% radial movement vs 2.7% · 3.2% tangential movement vs 4.6%

Closest overall match

If Merbau is unavailable and the specification cannot change, these are the nearest substitutes across hardness, density, movement, stiffness, bending strength and durability class together — not on any single property. Lower distance means a closer match.

Indian Rosewoodmatch 1.782,440 lbf · 0.75 g/cm³ · Class 12,440 lbf vs 1,712 · 0.75 vs 0.74 g/cm³ Jarrahmatch 1.881,910 lbf · 0.82 g/cm³ · Class 11,910 lbf vs 1,712 · 0.82 vs 0.74 g/cm³ · more stable (Excellent)Burma Teak Premium Gradematch 1.901,070 lbf · 0.66 g/cm³ · Class 11,070 lbf vs 1,712 · 0.66 vs 0.74 g/cm³

Computed from measured properties only — hardness, density, movement, stiffness, bending strength and EN 350 class. Price, availability and appearance are never inputs. Figures are representative values, not consignment absolutes: two species within a few percent are equivalent until verified on the material. Full method and the rules the engine cannot break.

Substituting outdoors is a match on durability class and movement first. Colour and grain can be matched later; a wrong durability class shows up as a callback in three monsoons. Where two candidates are close, compare them directly before specifying.

Compare Merbau side by side

These are the head-to-heads that decide cladding, decking and exterior joinery specifications. Every pairing shows the measured figures side by side; full matrix in the comparison index.

Merbau vs BalauSide-by-side data · 1,700 lbf Merbau vs Shisham SissooSide-by-side data · 1,660 lbf Merbau vs Indian RosewoodSide-by-side data · 2,440 lbf

Calculators relevant to Merbau

Aimed at exterior detailing in Merbau: coverage, gaps, coating and durability checks. Full set in the tool index.

Timber Post & Column Load CalculatorConstruction Cladding Coverage CalculatorThermoWood Floor Joist Span CalculatorConstruction Screw Withdrawal & Shear Strength in WoodJoinery Wood Flooring CalculatorConstruction Compound Miter Angle CalculatorJoinery International 1/4-Inch Log Rule CalculatorMeasurement Log Taper CalculatorMeasurement

Understand the figures

Wood density reference — oven-dry vs air-dry basis · Moisture content — EMC, FSP and service conditions · Strength properties — MOR, MOE and what they govern · Durability & fire — EN 350 classes and E84 ratings.

Further reading. Wood moisture content explained · How to calculate board feet.

Common questions about Merbau

How hard is Merbau, and what does that mean in practice?

At 1,712 lbf (7,615 N) it sits in the hard range — it shrugs off dents and heavy traffic, which is why it suits busy floors, stair treads and worktops. The trade-off shows at the bench: keep cutters sharp, pre-drill every fixing, and work it more slowly than a medium hardwood.

Can Merbau be used outdoors without treatment?

Largely yes. It's rated Very Durable (Class 1) under EN 350, meaning the heartwood naturally resists decay and can handle exterior exposure — decking, cladding, garden furniture — without chemical preservatives. Two caveats worth knowing: the pale sapwood isn't durable, so it should be cut away for outdoor work, and 'durable' isn't 'immortal' — it'll still silver and weather, so a UV oil keeps the colour if you care about looks.

How much does Merbau move with humidity?

It has moderate movement — radial shrinkage near 2.7%, tangential near 4.6% (T/R ratio about 1.7). That's typical territory: nothing alarming, but worth planning for. Dry it to the moisture content that suits your service environment, leave expansion room on wide panels, and let it settle in the space for a few days before final fixing and it behaves well.

unverified no published source for this figure · FPL USDA FPL Wood Handbook GTR-190 · WD The Wood Database (Eric Meier) · calc derived from the figures above

Tools that use this species

Janka Database ToolHardness for 60 species Green Weight CalculatorWeight of green timber Shrinkage PredictorDimensional movement EMC CalculatorEquilibrium moisture content Fiber Saturation CalculatorFSP by species Volume Converterm3, CFT, board feet

Sources & references

The Wood Database (Eric Meier) — compiled species data, one of the references behind the panel above. Which figure comes from which reference is not recorded field by field. Spot checks show the numbers do trace to published sources, but not all to the same one: strength values for US species follow the USDA FPL Wood Handbook exactly, while European species draw on European references instead. So a figure that disagrees with any single reference here is not necessarily wrong — different bodies measure specific gravity and shrinkage on different bases. If a number matters to your work, check it against the reference you intend to rely on.
CIRAD Tropix — tropical-timber technological database (Merbau / Intsia bijuga sheet) · durability, movement, uses
ITTO — International Tropical Timber Organization species database · sawing, machining, fastening, gluing
EN 350 — European standard for natural durability of wood · durability class

Updated 15 Jul 2026 Values are representative; wood varies with provenance, age and grade. Confirm critical structural or fire figures against a test report for your actual product.