What is merbau?
The Wood Guide · The wood register
Tropical hardwood · referenceMerbau
Warm reddish brown with yellow mineral deposits, very stable and very durable. With one property that can ruin any deck if you don't know about it.
- Intsia bijuga / palembanica
- Class 1–2
- Bleeds tannin
MerbauIntsia bijuga
Merbau in brief
From the forests of Southeast Asia: Intsia bijuga and Intsia palembanica, trees that grow up to 45 metres tall with a branch-free trunk of 15 to 25 metres.
The colour ranges from yellowish brown through reddish brown to greyish brown, with the characteristic yellow mineral deposits that show as small flecks in the surface. The structure is even and firm, which makes merbau excellent for precision work.
The heartwood reaches durability class 1–2 and is also exceptionally dimensionally stable — it moves little as humidity changes. That very combination made it the most popular decking and flooring wood in the Low Countries for years.
Merbau trees grow scattered through the forest, on average one per two hectares. That makes targeted harvesting labour-intensive and puts pressure on the forest: to reach a single tree, skid trails are often cut through untouched woodland. It is one of the reasons the species is considered vulnerable.
- Botanical
- Intsia bijuga, Intsia palembanica
- Origin
- Southeast Asia
- Tree
- up to 45 m, branch-free trunk 15 to 25 m
- Colour
- yellowish brown to reddish brown and greyish brown
- Structure
- even and firm — suited to precision work
- Durability
- class 1–2 (heartwood)
To be fair: merbau bleeds. The wood contains a lot of water-soluble tannin, and rain washes it out as a rust-brown liquid that permanently stains paving, walls and joints. On a new deck this can go on for months. If you lay merbau above light-coloured paving, you need to know this before installation — not after.
Up to 45 metres tall
Merbau comes from Intsia bijuga and Intsia palembanica, trees that grow up to 45 metres tall with a branch-free trunk of 15 to 25 metres. The heartwood reaches durability class 1 to 2 and is exceptionally stable.
Click a chapter or use the arrows · forest and flecks schematic, months of bleeding speeded up.
What merbau can do
| Property | Description |
|---|---|
| Colour | Ranging from yellowish brown to reddish brown and greyish brown, with yellow mineral deposits |
| Structure | Even and firm, ideal for precision work |
| Durability | Very durable — class 1–2 for the heartwood |
| Stability | Exceptionally dimensionally stable; moves little with changes in moisture |
| Hardness | High — hard-wearing enough for heavily used floors |
| Working | Pre-drilling essential; the mineral deposits blunt tools |
The yellow flecks in merbau are mineral deposits — silica-like inclusions the tree took up from the soil. They are harder than steel and blunt every saw blade and router bit noticeably faster. Plan on using carbide-tipped tools.
Dealing with tannin bleed
This is where most merbau decks go wrong. The first showers after installation wash water-soluble tannin out of the wood, and it runs as a rust-brown liquid over everything below or beside it. On light paving, white grout or a rendered wall, the stain is permanent.
- Rinse before installationLeave the boards outside for a few weeks and rinse them repeatedly, so the worst is out before they are laid.
- Protect what lies beneathCover adjoining paving and walls with plastic sheeting or a tarpaulin during the first months.
- Rinse off straight awayFresh bleed still comes off with plenty of water. Dried-in tannin needs a stain remover — and that does not always work.
- Or choose something elseAbove light-coloured paving, ipé or bangkirai is a safer choice, although it bleeds slightly too.
What merbau is used for
Decking and boardwalks
The classic use: hard, durable and dimensionally stable. Provided you plan for the bleeding.
Indoor flooring
Here the bleeding is not an issue and the stability comes fully into its own.
Exterior joinery
Window frames and doors: it moves so little that dimensional stability is no concern.
Furniture
For precision work thanks to its even structure, although it is heavy.
We do not use merbau. The combination of vulnerable forest stocks, scattered growth and the bleeding problem makes it an illogical choice for garden furniture; teak does the same job without those drawbacks.
Frequently asked questions about merbau
Why does my deck turn things brown after rain?
Merbau contains a lot of water-soluble tannin, which rain washes out as a rust-brown liquid. On light paving and grout the staining is often permanent. Rinse the boards repeatedly before installation.
How long does merbau keep bleeding?
Most heavily in the first months, and it can go on for a whole season. After that it tails off and largely disappears.
What are the yellow flecks in merbau?
Mineral deposits the tree took up from the soil. They are part of the wood, but they are harder than steel and blunt your tools faster.
Is merbau a sustainable choice?
The wood is durable — class 1–2. The species is another matter: merbau trees grow very scattered, which makes harvesting hard on the forest, and the species is considered vulnerable. Always ask where it comes from.
Merbau in perspective
Excellent wood with one property you need to know about beforehand.
Have a question about your project? Just ask — we're happy to help.
Intsia spp. — Alina Zienowicz, CC BY-SA 3.0 · Intsia bijuga — Denis Prévôt, CC BY-SA 3.0 · Photo via Wikimedia Commons: Intsia bijuga — Steve Fitzgerald, CC BY-SA 4.0