Yellow Balau (Bangkirai) Decking Boards Smooth 21x145mm

Yellow Balau — also known as Bangkirai — is one of the most popular and widely used tropical hardwood decking species in the UK. These smooth-face Balau decking boards at 21x145mm deliver a premium deck surface with a rich golden-brown tone, exceptional density, and a natural durability class of 1–2, giving them an expected service life of 25 years or more without chemical treatment.

At 21mm thick and 145mm wide, these boards produce a solid, confident deck surface with fewer board runs per square metre than narrower profiles — covering ground quickly and creating a bold, contemporary appearance that suits residential gardens, commercial terraces, pool surrounds, and public realm projects equally well.

Product Specifications

What Is Yellow Balau (Bangkirai)?

Yellow Balau and Bangkirai are the same species — Shorea laevifolia from the Dipterocarpaceae family, native to the lowland forests of Malaysia and Indonesia. Yellow Balau is the name used in UK and Malaysian trade; Bangkirai is the Indonesian and Dutch trade name. Both refer to the same dense, fine-grained tropical hardwood that has been a benchmark decking timber across Europe for decades.

Fresh-sawn Balau boards have a distinctive golden-yellow to warm mid-brown colour with occasional reddish-brown streaks that give each deck a naturally varied, characterful appearance. The timber is extremely dense — around 980 kg/m³ — which translates to excellent wear resistance underfoot, outstanding resistance to surface denting, and a natural hardness that makes it one of the most durable hardwood decking options available in the UK.

Its natural oil content, similar in composition to teak, gives Yellow Balau inherent resistance to rot, fungal decay, and wood-boring insects without chemical treatment. This is why it has historically been used in marine construction, bridge building, and heavy outdoor structures — applications where structural longevity in wet conditions is critical. For garden decking, patios, terraces, and commercial outdoor spaces in the UK, it represents one of the most long-lasting and low-maintenance choices available.

Durability and Lifespan

Yellow Balau hardwood decking achieves a natural durability class of 1–2 — the highest rating for timber used above ground outdoors. In standard above-ground residential and commercial decking applications it has an expected service life in excess of 25 years. With periodic oiling and basic maintenance, service lives of 40 years or more are regularly achieved; in some protected applications up to 75 years has been recorded.

Its high density also makes Bangkirai decking particularly well suited to high-traffic areas where softer timbers would show surface wear far sooner — commercial hospitality terraces, poolside decking, public boardwalks, and communal garden spaces where the deck will see heavy daily use.

Yellow Balau is naturally resistant to the repeated wet-dry cycles of the UK climate, which cause many softer decking timbers to warp, cup, and split over time. Its interlocking grain structure further resists movement, keeping boards flat and stable year after year.

Installation

These Balau decking boards are face fixed. Because Yellow Balau is an exceptionally dense hardwood — one of the densest available for UK decking — pre-drilling pilot holes before driving screws is essential, not optional. Driving screws without pilot holes will split the board and shear the screw head. Use stainless steel A2 or A4 screws throughout; the natural tannins and oils in Bangkirai react with lower-grade metals and cause surface staining that cannot be removed without sanding.

Leave a 5–6 mm gap between boards for drainage and seasonal movement. Allow boards to acclimate on site for a minimum of 48–72 hours before installation to stabilise their moisture content relative to the installation environment. Seal all cut ends immediately after cutting with a hardwood end-grain sealer or decking oil to limit moisture uptake at exposed grain.

Install boards on a level, well-ventilated subframe with joists at a maximum of 400mm centres for residential use, or 300mm centres for commercial and high-traffic applications. We stock stainless steel screws and hardwood decking oils and stains suitable for Yellow Balau.

Finishing and Maintenance

Balau hardwood decking does not require treatment to maintain its structural performance. Left untreated, the boards will weather from their warm golden-brown to a uniform silver-grey over approximately 12–18 months — a natural oxidation process that does not affect durability or lifespan. Many customers prefer the silvered appearance for its low-maintenance, contemporary look.

To retain the original warm golden-brown colour of the Yellow Balau, apply a UV-stable penetrating hardwood decking oil before installation and reapply annually or as the surface demands. Keep the deck clear of leaf debris and organic matter which can accelerate surface staining. Avoid pressure washing — clean with a brush, warm water, and mild soap instead. We stock Remmers and Koopmans hardwood oils and stains that are well suited to dense tropical hardwoods including Yellow Balau and Bangkirai.

Yellow Balau vs ThermoWood Decking

Both Yellow Balau hardwood decking and ThermoWood are premium long-life decking options that outperform untreated softwood significantly in durability and maintenance. They suit different project priorities. Balau is exceptionally hard and dense — ideal for high-traffic, high-wear environments and projects where maximum natural hardness and a traditional warm hardwood tone are the priority. Our ThermoWood secret fix decking range offers thermally modified pine with a hidden fixing system producing a completely screw-free surface, superior dimensional stability, and a chemical-free treatment process. Both are excellent choices — the right decision depends on your preferred finish, fixing method, and project specification.

Frequently Asked Questions