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| Name | balau |
| Other Names | bangkirai, benuas, damar laut, simantuk, poöti (Indonesia), bangkirai (The Netherlands), yellow balau (Malaysian Penninsula), selangan batu, selangan batu kumus, balau kumus, tekam (North Borneo, Sarawak), gisok, malayakal, yakal (The Philippines), aek, las-tao, chan (Thailand), song-da (Vietnam). |
| Botanical Name | Shorea atrivernosa Sym., S. foxworthyi Sym., S. gisok Foxw., S. glauca King, S. laevis Ridl. (= S. laevifolia (Paris) Endert), S. maxwelliana (v. Sl. ex Foxw.) Sym., S. spec. div. Section: Shorea, Neohopea (Ashton 1983). |
| Family | Dipterocarpaceae. |
| Origin | Southeast Asia. Principally supplied from the Malaysian federal states of Sabah and Sarawak. |
| Tree Description | Trees from the Shorea species grow to heights of 35 to 40 m depending on their location (max. 60 m). Older trees often have 1 to 3 m high root buttresses. Branch-free trunk lengths vary from 20 to 25 m, diameters between 0.6 and 0.8 m (max. 2 m) and are generally straight. |
| Available As | Planed timber |
| Wood Description | Balau heartwood is yellow to greyish brown when freshly cut, sometimes with a reddish tint. In daylight, it initially discolours fast to brown and then more slowly to dark brown. The white to light brown sapwood stands out clearly from the heartwood and measures 20 to 70 mm. Balau has a fine and even structure and usually a strong interlocked grain with a clear striped patterning on radial or quarter-sawn surfaces. Axial resin ducts often occur in tangential rings and form whitish stripes on longitudinal surfaces. Except for occasional pinholes (small wormholes), small resin pockets and surface cracks, the wood is virtually blemish free. |
| Wood Type | Hardwood |
| Grain | Strong interlocked grain, but straight and undulating grains also exist. |
| Texture | Fine to moderately coarse. |
| Density | 700/930/1150 kg/m3 at 12% humidity. |
| Working | Average to major depending on type. |
| Drying | Very slow. Although shrinkage is moderate, the wood is susceptible to surface cracking and end splitting, particularly when exposed to sunlight and when dried too quickly. Must be dried very carefully and slowly. |
| Workability | Despite its hardness, balau can be cut to length, sawn and planed fairly easily. A lot of chipped grains can arise due to interlocked grain when planing quarter-sawn surfaces. A proper chip angle can improve matters considerably. |
| Fixings and Fasteners | Pre-drilling required. Under humid conditions, always use non-corrosive fasteners. |
| Bonding | Poor. |
| Pliability | Supposedly poor. |
| Surface Finishing | Poor. Finishing with neutral varnish, stain or alkyd resin paint can cause problems. Take account of rapid discolouration when applying neutral finishes. Fine cracks arising in the wood surface can cause the surface finish to blister, crack and peel fairly quickly when exposed to the elements. Bonding properties are good. In general, this wood type is used where no further finishing is required. |
| Durability | Mould 2 (for wood with a density greater than 850 kg/m3 at a humidity of 12%). Termites D. Balau/bangkirai/selangan batu is also very resistant to acids and other chemical substances. |
| Strength Class | - |
| Impregnability | Heartwood 4. Sapwood 1 - 2. |
| Peculiarities | Several of these woods contain a water-soluble resin. This water-soluble resin can result in brown stains (bleeding) on underlying areas. These stains often disappear after a few months. Staining can often be prevented by thoroughly washing and scrubbing surfaces before applying any surface finishes. If portions of wood are exposed to the elements, bleeding may again occur even after several years due to seepage of resin through newly formed cracks. Balau and selangan batu are botanically a hybrid of a large number of principally Shorea varieties with a wide range of properties. Densities vary the most with heavier varieties having better resistance to mould and insects than their lighter siblings. To prevent too large a discrepancy in material properties (including durability) from arising, a lower limit is set for the density of all batches of selangan batu supplied. According to Malaysian certification rules for sawn hardwoods (1984), the density of balau/selangan batu should lie between 850 and 1155 kg/m3 at a humidity of 15%. In theory, this weight class is traded under the names selangan batu or bangkirai. Bangkirai is the original name for Shorea laevis Ridl (= Shorea laevifolia (Paris) Endert) originating from Indonesia, but batches consisting solely of this wood type are no longer available. Bangkirai is often called selangan batu or balau kumus and on account of its density and belongs to the Malaysian balau/selangan batu group. Timber traded in the Netherlands is principally sold under the name bangkirai for Shorea wood varieties described above. |
| Applications | Due to its excellent mechanical properties and durability, Balau is extremely well suited to outdoor usage for heavy-duty construction, bridges, bridge decks and railings, sound barriers, locks and other freshwater hydraulic engineering structures such as sheetpiling, jetties, etc. It is also suitable for industrial and wagon flooring, posts, crossbeams, vessels, fences, gates, pergolas and park benches. |
| Quality Requirements | Balau is listed in Dutch usage guidelines, NPR5493:1999, Kwaliteitsrichtlijnen voor loofhout in waterbouwkundige werken ['Quality Directives for Hardwood Used in Hydraulic Engineering Projects']. Balau meets requirements specified in evaluation directive BRL 2351/01 Mestbassins van hout ['Wooden Slurry Tanks']. |
Source: Houtvademecum, 8e druk 2001