Merbau has been Australia’s go-to hardwood decking timber for decades. It’s affordable for a hardwood, naturally durable, and has that rich reddish-brown colour that looks stunning when freshly oiled. But composite decking has rapidly gained ground as homeowners discover the long-term advantages of engineered boards over natural timber.
If you’re deciding between composite and merbau decking for your next project, this guide gives you the full picture — the genuine pros and cons of each material, with honest comparisons across cost, maintenance, durability, appearance, and more.
What Is Composite Decking? Complete Guide →
Quick Comparison: Composite vs Merbau Decking
| Factor | Composite Decking | Merbau Decking |
| Material Cost | $100–$250/m² | $100–$160/m² |
| Installed Cost | $250–$450/m² | $250–$400/m² |
| Annual Maintenance | Wash only ($0) | Oil/stain ($300–$800/yr) |
| Lifespan | 25–30+ years | 20–25 years (maintained) |
| Tannin Bleeding | None | Significant (stains concrete) |
| Termite Resistance | Fully resistant | Naturally resistant (Class 1–2) |
| Splinters | None | Common as timber ages |
| Colour Without Oiling | Does not require oiling to maintain its appearance | Turns silver-grey |
| Colour With Oiling | Not required | Rich reddish-brown |
| Installation Speed | 50–70% faster | Standard |
| Bushfire Rating | Up to BAL-29 | BAL-29 (naturally) |
| Warranty | 15–30 years | Rarely offered |
| 20-Year Total (30m²) | $9,000–$14,000 | $14,000–$28,000 |
What Is Merbau Decking?
Merbau (Intsia bijuga) is a tropical hardwood native to South-East Asia, widely used in Australian decking for its combination of affordability, durability, and rich colour. It’s classified as a Class 1–2 durability timber, meaning it has good natural resistance to rot and decay, and reasonable resistance to termites.
Merbau’s popularity in Australia comes down to price — it’s one of the most affordable hardwood options, typically costing $100–$160 per square metre for kiln-dried boards. When freshly oiled, merbau has an attractive reddish-brown colour with a tight, interlocking grain pattern that many homeowners love.
However, merbau comes with several well-known issues that are worth understanding before you commit — particularly tannin bleeding, ongoing maintenance demands, and sustainability concerns around tropical timber sourcing.
Cost Comparison: The Full Picture
Upfront Material and Installation Costs
Merbau and composite decking are surprisingly similar in upfront cost. Merbau boards typically cost $100–$160 per square metre, while mid-range to premium composite ranges from $100–$250 per square metre. When you add subframe, fasteners, and installation labour, the total installed costs overlap significantly.
Composite installs 50–70% faster than merbau due to hidden fastening systems and consistent board dimensions. Merbau requires pre-drilling every screw hole to avoid splitting, individual board selection for straightness, and careful handling to manage the oily surface. This labour difference often means composite installation costs less per square metre despite higher material prices.
Long-Term Cost: Where Composite Wins Decisively
The real cost difference between composite and merbau emerges over time. Merbau decking requires annual oiling (or bi-annual at minimum) to maintain its colour and protect the timber. A typical 30m² deck costs $300–$800 per year to maintain, depending on whether you DIY or hire a professional. Over 20 years, that’s $6,000–$16,000 in maintenance costs alone.
Composite decking needs nothing beyond occasional cleaning with soapy water. No oil, no stain, no sealer — ever. When you run the numbers over 20 years, composite typically saves $5,000–$14,000 compared to merbau.
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The Tannin Bleeding Problem
This is one of the most common complaints about merbau decking, and one that many homeowners don’t discover until after installation.
Merbau contains high levels of natural tannins — water-soluble compounds that leach out of the timber when exposed to moisture. When it rains, these tannins wash out of the boards and stain everything they touch: surrounding concrete, pavers, rendered walls, pool coping, paths, and even clothing and outdoor furniture. The staining is a distinctive reddish-brown colour that is extremely difficult to remove.
Tannin bleeding is most severe in the first 6–12 months after installation but can continue for 2–3 years or longer, depending on rainfall and board thickness. While tannin staining can be managed with commercial tannin removers and sealers, it’s an ongoing frustration that catches many homeowners by surprise — especially around pool areas where tannin-stained concrete is both unsightly and difficult to clean.
Composite decking produces zero tannin bleeding, making it the significantly better choice for pool surrounds, areas adjacent to light-coloured paving, and any application where staining would be a problem.
Durability in Australian Conditions
Merbau Durability
Merbau is a genuinely durable hardwood, classified as Durability Class 1–2 (above ground) and Class 2 (in ground). It has natural resistance to rot and moderate termite resistance, and a Janka hardness rating of approximately 8.5 kN, making it hard-wearing underfoot.
However, merbau isn’t bulletproof. Without regular oiling, it cracks, cups, and splits as moisture levels fluctuate with Australia’s seasonal changes. Surface checking (small cracks along the grain) is common and accelerates if maintenance lapses. Merbau is also susceptible to movement — boards can warp, twist, or bow, particularly if not kiln-dried properly or if the subframe allows excessive moisture exposure.
In coastal environments, merbau performs reasonably well but still requires diligent maintenance to manage salt exposure. In high-humidity regions like South-East Queensland, mould and mildew growth on merbau surfaces can become an ongoing issue.
Composite Decking Durability
Composite decking is engineered to handle everything Australia’s climate throws at it. Premium capped composite boards won’t rot, warp, crack, cup, split, or splinter. They’re completely resistant to moisture, mould, mildew, and termites. UV stabilisers and ASA capping are designed to improve performance under UV exposure, with warranties primarily covering structural integrity and limited appearance factors, subject to product, installation, and site conditions.
Composite performs particularly well in the conditions where merbau struggles most: poolside installations (no tannin, excellent slip resistance), coastal properties (salt and moisture resistance), and high-humidity subtropical climates (mould and mildew resistance).
Maintenance: A Major Lifestyle Difference
Maintaining Merbau Decking
Merbau decking demands a consistent maintenance routine to stay in good condition. The typical annual schedule includes cleaning the deck surface thoroughly, sanding any rough patches or raised grain, applying 1–2 coats of quality decking oil, and inspecting for signs of decay, splitting, or termite activity.
This process takes a full weekend for a typical 30m² deck and costs $300–$800 per year in materials (quality hardwood oil isn’t cheap). Many homeowners hire a professional to oil their deck, which adds to the annual cost.
The reality is that merbau maintenance is not optional. Skip a year and the timber’s protective oil layer breaks down, moisture penetrates the wood, and the deterioration cycle accelerates. Within 2–3 years of neglect, a merbau deck can go from looking good to needing significant repairs or board replacement.
Maintaining Composite Decking
Composite decking maintenance is minimal: sweep away debris regularly and wash with warm soapy water and a soft brush 2–4 times per year. No oiling, no staining, no sealing, no sanding — ever. Most homeowners spend a couple of hours per year on composite deck maintenance, compared to full weekends on merbau.
This maintenance difference is the single biggest reason homeowners switch from timber to composite when replacing an aging deck. After years of annual oiling commitments, the appeal of a maintenance-free deck is significant.
Appearance: Natural Timber vs Engineered Aesthetics
Freshly oiled merbau is undeniably attractive. The rich reddish-brown colour, natural grain variation, and warm timber feel are appealing, and for some homeowners, the authentic look of real hardwood is a non-negotiable priority.
The catch is that merbau only looks that good immediately after oiling. Within weeks, the surface begins to dull. Within months, without re-oiling, it starts greying. After a year, an unoiled merbau deck looks nothing like the day it was installed — it fades to a flat, silver-grey colour that most homeowners find unattractive.
Modern composite decking addresses this with sophisticated manufacturing techniques. Multi-tonal colour blending, realistic grain patterns, and natural colour variation create a convincing timber aesthetic. Premium composite ranges now offer boards that closely replicate the look of popular hardwoods including merbau, spotted gum, and blackbutt — with the advantage of more consistent appearance over time, without the regular oiling required by timber.
Composite also offers colours that natural timber simply can’t — contemporary charcoals, modern greys, and warm silver tones that suit current architectural trends.
Explore Composite Colour Options →
Safety: Families, Pools, and Bushfire Zones
Splinters: Merbau develops splinters as it ages, particularly on high-traffic areas and board edges. This is a real hazard for bare feet, young children, and pets. Composite decking is completely splinter-free for its entire lifespan.
Slip resistance: Many composite decking products are manufactured with textured surfaces rated R11/P5 (product dependent). Merbau can become slippery when wet, especially once the surface oil wears off and a biofilm develops. Around pools, composite’s consistent slip resistance is a significant safety advantage.
Bushfire zones: Both materials can perform well in bushfire-prone areas. Merbau is naturally rated to BAL-29, and some composite products (including our NextGen Titanium range) also achieve BAL-29 certification. Check specific product ratings for your BAL zone.
Pool surrounds: Composite is the clear winner for pool decking. No tannin bleeding (which stains pool coping and surrounding concrete), excellent slip resistance when wet, no splinters on bare feet, and no chemical treatments that could affect pool water.
Sustainability and Environmental Impact
The environmental credentials of merbau are a genuine concern. The majority of merbau timber is sourced from tropical forests in Papua New Guinea, Indonesia, and the Pacific Islands. Illegal logging has been a documented problem in these regions, and even legally sourced merbau involves harvesting slow-growing tropical hardwood from complex ecosystems.
While FSC-certified merbau is available, it represents a small fraction of the market, and supply chain transparency remains a challenge. The carbon footprint of harvesting, processing, and shipping tropical timber to Australia also adds to the environmental impact.
Composite decking takes a fundamentally different approach. Most composite boards are manufactured from recycled materials — reclaimed wood fibres and recycled plastics (typically HDPE from post-consumer waste like milk bottles and plastic bags). By choosing composite, you’re diverting plastic from landfill and reducing demand for virgin timber. The absence of ongoing chemical treatments (oils, stains, sealers) further reduces the environmental footprint over the deck’s lifetime.
Installation Differences
Merbau is a dense, heavy hardwood that requires skill and patience to install well. Every screw hole must be pre-drilled to avoid splitting, and countersinking is necessary for a flush finish. Boards need to be individually selected for straightness (merbau is prone to bowing and twisting), and the natural oils in the timber can make handling and fastening more challenging. Installation time is significant, which directly impacts labour costs.
Composite decking installs 50–70% faster than merbau. Hidden fastening systems create a clean, screw-free surface without any pre-drilling. Boards are manufactured to exact, consistent dimensions, so there’s no sorting for straightness or rejecting warped boards. This speed advantage translates to real labour savings — often enough to offset the higher material cost of composite.
For DIY projects, composite is the more forgiving material. The hidden clip systems are straightforward, board dimensions are predictable, and there’s no risk of splitting. Merbau DIY installation requires more tools, more skill, and more patience to achieve a professional result.
When to Choose Composite Over Merbau
- You want zero ongoing maintenance — no oiling, staining, or sealing commitments
- You’re building near a pool or water feature — no tannin bleeding, superior slip resistance
- Long-term value is your priority — save $5,000–$14,000 over 20 years
- You want consistent colour for decades — no greying from lack of oiling, and reduced appearance changes compared to natural timber.
- Safety matters — splinter-free, slip-resistant surfaces for families
- Sustainability is important to you — recycled materials vs tropical hardwood harvesting
- You’re in a high-humidity area — mould and mildew resistance without chemical treatment
When Merbau Might Still Be the Right Choice
- Authentic natural timber is non-negotiable — you want the real look and feel of hardwood and you’re committed to maintaining it
- You enjoy annual deck maintenance — some homeowners find the oiling ritual satisfying
- You’re matching existing merbau features — extending or complementing an existing merbau structure
The Bottom Line
Merbau has served Australian homeowners well for decades, and it remains a solid hardwood option for those who value natural timber and are committed to its upkeep. However, for the majority of homeowners, composite decking offers a better overall package: comparable upfront cost, dramatically lower lifetime cost, zero maintenance, superior durability in Australian conditions, and none of the issues that frustrate merbau owners — no tannin bleeding, no greying, no splinters, no annual oiling weekends.
Our recommendation: Request free samples of both materials and compare them side by side. Many homeowners who were set on merbau are genuinely surprised by how close premium composite looks and feels — and once they factor in the 20-year cost difference and maintenance reality, the decision makes itself.
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Frequently Asked Questions
Is composite decking more expensive than merbau?
Upfront, composite and merbau are similar in cost — both typically range from $250–$450 per square metre installed. However, composite eliminates annual maintenance costs of $300–$800, making it significantly cheaper over the life of the deck. Most homeowners break even within 3–5 years compared to merbau.
Does merbau decking stain concrete?
Yes. Merbau contains natural tannins that leach out when exposed to rain, leaving reddish-brown stains on surrounding concrete, pavers, walls, and other surfaces. This tannin bleeding is most severe in the first 12 months but can continue for 2–3 years. Composite decking doesn’t have this problem.
How long does merbau decking last compared to composite?
Well-maintained merbau decking lasts approximately 20–25 years, though individual boards may need replacing sooner. Premium composite decking lasts 25–30+ years with minimal maintenance and typically comes with manufacturer warranties of 15–30 years.
Can I replace my merbau deck with composite?
Yes, and this is one of the most common renovation projects we see. In some cases, the existing timber subframe can be reused if it’s structurally sound. Your installer can assess the existing framework and advise whether it can support composite boards or needs upgrading.
Is merbau decking sustainable?
Merbau sustainability is a genuine concern. Most merbau comes from tropical forests in South-East Asia and the Pacific, where illegal logging has been documented. FSC-certified merbau is available but represents a small portion of the market. Composite decking, made from recycled wood fibres and plastics, offers a more environmentally responsible alternative.
Which is better around a pool — composite or merbau?
Composite is the significantly better choice for pool areas. It doesn’t produce tannin stains that discolour pool coping and surrounds, offers consistent slip resistance when wet (including R11/P5 slip rating on specific boards), is completely splinter-free on bare feet, and requires no chemical treatments near pool water.
Does composite decking look like merbau?
Premium composite ranges now include colours and grain patterns specifically designed to replicate the merbau aesthetic. While no engineered product perfectly matches natural timber, the resemblance is remarkably close — and composite maintains a more consistent appearance over time, unlike merbau which greys without regular oiling.
Upfront, composite and merbau are similar in cost — both typically range from $250–$450 per square metre installed. However, composite eliminates annual maintenance costs of $300–$800, making it significantly cheaper over the life of the deck. Most homeowners break even within 3–5 years compared to merbau.
Yes. Merbau contains natural tannins that leach out when exposed to rain, leaving reddish-brown stains on surrounding concrete, pavers, walls, and other surfaces. This tannin bleeding is most severe in the first 12 months but can continue for 2–3 years. Composite decking doesn’t have this problem.
Well-maintained merbau decking lasts approximately 20–25 years, though individual boards may need replacing sooner. Premium composite decking lasts 25–30+ years with minimal maintenance and typically comes with manufacturer warranties of 15–30 years.
Yes, and this is one of the most common renovation projects we see. In some cases, the existing timber subframe can be reused if it’s structurally sound. Your installer can assess the existing framework and advise whether it can support composite boards or needs upgrading.
Merbau sustainability is a genuine concern. Most merbau comes from tropical forests in South-East Asia and the Pacific, where illegal logging has been documented. FSC-certified merbau is available but represents a small portion of the market. Composite decking, made from recycled wood fibres and plastics, offers a more environmentally responsible alternative.
Composite is the significantly better choice for pool areas. It doesn’t produce tannin stains that discolour pool coping and surrounds, offers consistent slip resistance when wet (including R11/P5 slip rating on specific boards), is completely splinter-free on bare feet, and requires no chemical treatments near pool water.
Premium composite ranges now include colours and grain patterns specifically designed to replicate the merbau aesthetic. While no engineered product perfectly matches natural timber, the resemblance is remarkably close — and composite maintains a more consistent appearance over time, unlike merbau which greys without regular oiling.
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