Chengal for Custom Epoxy River Tables
Chengal (Neobalanocarpus heimii, synonymous with Balanocarpus heimii) is a heavy timber from Asia-Oceania renowned for its exceptional strength and outdoor performance. According to the CIRAD Tropix technical sheet, Chengal is historically relied upon for demanding structural applications like bridges, decking, and railway sleepers. For woodworkers building custom epoxy river tables and solid tabletops, Chengal offers striking deep tones and formidable mechanical properties, but its high density and resinous nature require disciplined shop preparation.
Appearance, Weight, and Hardness
Chengal heartwood exhibits a brown color that varies from brown-olive to red-brown, sharply demarcated from a sapwood layer ranging from 2 to 5 cm thick. The wood has a medium texture, a slight interlocked grain, and localized resinous areas. Slabs cut from logs measuring 70 to 150 cm in diameter provide substantial widths for statement tabletops.
It is a dense timber with a specific gravity of 0.91 at 12% moisture content (about 56.8 lb/ft³). A standard 2-inch-thick tabletop slab weighs approximately 9.5 lb per square foot. While standard CIRAD Tropix testing sheets assess wood hardness using the French Monnin hardness scale (where a higher rating signifies harder wood, a measure that should never be converted to Janka), the Chengal data sheet leaves the Monnin number unlisted, qualitatively categorizing Chengal simply as a hard wood. Its mechanical strength confirms this: crushing strength is 75 MPa (about 10,880 psi), static bending strength reaches 134 MPa (about 19,440 psi), and modulus of elasticity is 24,300 MPa (about 3,524,000 psi).
Dimensional Stability and Shrinkage Next to Epoxy
When pairing timber with rigid epoxy casting resins, managing wood movement across humidity cycles is paramount. Chengal exhibits total tangential shrinkage of 7.4% and total radial shrinkage of 3.0%, yielding an St/Sr ratio of 2.5. An St/Sr ratio significantly higher than 1.0 indicates a notable tendency toward cupping across flat-sawn boards. Because the wood is stiff and dense, any movement against an epoxy river interface can generate intense shear stress.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Neobalanocarpus heimii, Balanocarpus heimii (synonymous) | |
| Colour / texture / grain | Brown; texture medium; grain interlocked; interlocked grain slight | |
| Specific gravity (12% MC) | 0.91 | about 56.8 lb/ft³; a 2-inch-thick slab weighs about 9.5 lb per sq ft |
| Total tangential shrinkage | 7.4 % | green to oven-dry |
| Total radial shrinkage | 3.0 % | green to oven-dry |
| Ratio St/Sr | 2.5 | closer to 1 = less cupping tendency |
| Thermal conductivity | 0.29 W/(m·K) | |
| Crushing strength (12% MC) | 75 MPa | about 10,880 psi |
| Static bending strength (12% MC) | 134 MPa | about 19,440 psi |
| Modulus of elasticity (12% MC) | 24,300 MPa | about 3,524,000 psi |
| Decay (fungi) resistance | Durability class 1 – very durable | |
| Termite resistance | Class D – durable | |
| Dry-wood borer resistance | Class D – durable (sapwood demarcated, risk limited | |
| Heartwood treatability | Class 4 – not permeable | |
| Use class from natural durability | Class 4 – in ground or fresh water contact | |
| Drying | rate slow; distortion: high risk; checking: slight risk; collapse: no known specific risk; casehardening: no known specific risk | |
| Suggested kiln program temperatures | 45–65 °C | about 113–149 °F |
| Machining | blunting fairly high; saw teeth: stellite-tipped; cutting tools: tungsten carbide | |
| Nailing and screwing | Good but pre-boring necessary | |
| CITES status | This species is not listed in the CITES Appendices (Washington Convention 2025). |
Values from the CIRAD Tropix technical sheet (average values for mature wood, 12% moisture content where noted). US-unit conversions are calculated by BigEpoxy (1 MPa = 145.04 psi; density = specific gravity × 62.43 lb/ft³).
Pros and Cons of Chengal for Epoxy Tabletops
Pros
- Natural Durability: Ranked as Durability Class 1 (very durable against decay fungi), Class D against termites, and Class D against dry-wood borers (with borer risk limited to the demarcated sapwood).
- Extreme Rigidity: With a modulus of elasticity of 24,300 MPa, table slabs resist deflection over wide spans.
- Clear Visual Contrast: Clearly demarcated sapwood (2 to 5 cm) offers natural live-edge definition against dark brown or red-brown heartwood.
- Regulatory Status: Not listed in the CITES Appendices (Washington Convention 2025).
Cons
- Distortion Risk: CIRAD Tropix reports a high risk of distortion during drying, paired with a slow drying rate.
- Severe Tool Wear: Blunting effect is fairly high, necessitating tungsten carbide cutting edges and stellite-tipped saw teeth.
- Resinous Interference: The presence of resin is troublesome during machining and can interfere with gluing.
- High Cupping Ratio: An St/Sr shrinkage ratio of 2.5 means flatsawn slabs require careful mechanical restraint.
Build Notes: Working with Chengal in the Shop
Slab Selection
Look for well-aligned, quarter-sawn stock when possible to avoid the differential movement represented by the 2.5 shrinkage ratio. Inspect the demarcated sapwood closely: while the heartwood is Class 1 durable and non-permeable (Class 4 treatability), sapwood remains vulnerable to dry-wood borers.
Drying
Chengal dries slowly and carries a high risk of distortion, though the risk of checking is slight and there is no known specific risk of collapse or casehardening. If kiln drying, Tropix recommends temperatures between 45 °C and 65 °C (about 113 °F to 149 °F). Ensure moisture is uniform and equilibrated to your shop before casting resin.
Machining
Tool blunting is fairly high. Use stellite-tipped saw blades and tungsten carbide cutters. Resinous areas in the wood will foul cutters rapidly, requiring frequent cleaning to prevent burning and poor surface quality.
Sealing, Gluing, and Epoxy Interface
CIRAD notes that because of Chengal’s high specific gravity and resin exudations, gluing must be performed strictly according to standard codes of practice. Before pouring an epoxy river or applying seal coats, thoroughly clean contact edges to clear surface resin. Always apply an epoxy seal coat along the live edges to block air expulsion from the medium-textured pores, following your resin manufacturer’s data sheet.
Fasteners and Base Mounting
Fastening requires pre-boring for all screws and bolts due to the timber’s extreme density and hardness. When attaching steel table bases, utilize slotted holes to accommodate the wood’s tangential movement across seasonal humidity swings.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: CIRAD Tropix notes that Chengal does not float, a direct result of its high 0.91 specific gravity; table makers should plan for substantial lifting assistance and heavy-duty shop carts when handling slabs over 70 cm wide. (Source: CIRAD Tropix 7 technical sheet: Chengal.)