Technical Overview of Rengas for Epoxy River Tabletops
Rengas is a distinctive tropical hardwood harvested from species such as Gluta beccarii, Gluta malayana, Gluta renghas, and other Gluta species. When planning a custom epoxy river table or mixed-material tabletop, knowing exact physical parameters helps woodworkers predict slab movement, edge adhesion, and tool longevity. The technical evaluation below draws directly from CIRAD Tropix research data to evaluate Rengas for fine furniture builds.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Gluta beccarii, Gluta malayana, Gluta renghas, Gluta p.p. | |
| Colour / texture / grain | Red brown; texture fine; grain straight to entangled; interlocked grain slight | |
| Specific gravity (12% MC) | 0.70 | about 43.7 lb/ft³; a 2-inch-thick slab weighs about 7.3 lb per sq ft |
| Monnin hardness (12% MC) | 2.5 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 5.3 % | green to oven-dry |
| Total radial shrinkage | 2.9 % | green to oven-dry |
| Ratio St/Sr | 1.8 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.29 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 25 % | |
| Thermal conductivity | 0.23 W/(m·K) | |
| Crushing strength (12% MC) | 49 MPa | about 7,110 psi |
| Static bending strength (12% MC) | 85 MPa | about 12,330 psi |
| Modulus of elasticity (12% MC) | 18,500 MPa | about 2,683,000 psi |
| Decay (fungi) resistance | Durability class 3 – moderately durable | |
| Termite resistance | Class M – moderately durable | |
| Dry-wood borer resistance | Class S – susceptible (risk in all the wood) | |
| Heartwood treatability | Class 3-4 – poorly or not permeable | |
| Use class from natural durability | Class 2 – inside or under cover (dampness possible) | |
| Drying | rate slow; distortion: no risk or very slight risk; checking: slight risk; collapse: no known specific risk; casehardening: no known specific risk | |
| Suggested kiln program temperatures | 53–65 °C | about 127–149 °F |
| Machining | blunting 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).
What does Rengas wood look like in a finished tabletop?
Rengas offers dramatic contrast for furniture and epoxy projects. According to CIRAD Tropix data, the heartwood is red brown to deep blood red and lustrous, naturally marked with dark, almost black stripes that darken further upon exposure to air and light. The sapwood is clearly demarcated from the heartwood, displaying a distinct white to pale yellow tone across a thickness of 10 to 20 cm. Logs range from 30 to 80 cm in diameter. The grain runs straight to entangled with slight interlock, complemented by a fine wood texture that finishes to an attractive, shiny luster.
How heavy and hard is Rengas lumber?
At 12% moisture content, Rengas has an average specific gravity of 0.70. This translates to an approximate density of 43.7 lb/ft³, meaning a 2-inch-thick slab weighs roughly 7.3 lb per sq ft. This medium-heavy mass gives dining tables and conference tables a substantial, rooted feel without being unmanageably heavy during fabrication.
Hardness is evaluated on the French Monnin scale at 2.5. Note that the Monnin scale is an independent European measurement where higher numbers indicate harder timber; it is not a Janka score and cannot be converted to one. For comparison within furniture use, this hardness level provides dependable resistance to daily wear across indoor surfaces.
How dimensionally stable is Rengas next to an epoxy river?
Differential movement between curing resin and solid timber is the primary cause of tabletop tension or joint separation. Rengas demonstrates moderate shrinkage values that favor dimensional stability once acclimated:
- Total tangential shrinkage: 5.3%
- Total radial shrinkage: 2.9%
- Tangential to radial ratio (St/Sr): 1.8
- Coefficient of volumetric shrinkage: 0.29% per 1% change in moisture content
- Fibre saturation point: 25%
An St/Sr ratio of 1.8 indicates a modest cupping tendency during seasonal humidity swings. With a volumetric shrinkage rate of 0.29% per percent of moisture change, properly sealed Rengas boards paired with an epoxy pour will experience predictable, controlled dimensional changes.
What are the drying behaviors and risks before pouring epoxy?
Rengas exhibits a slow drying rate, requiring patience during kiln or air seasoning. However, it displays excellent dimensional tolerance during moisture reduction. CIRAD Tropix records no risk or very slight risk of distortion, a slight risk of checking, and no known specific risk of casehardening or collapse. The suggested kiln schedule operates between 53 and 65 °C (about 127 to 149 °F). Prior to casting epoxy, wood must always be dried down to target indoor equilibrium moisture levels per the resin manufacturer’s technical instructions to avoid moisture-induced clouding or bond failure.
How does Rengas machine and what tools are required?
Machining Rengas demands durable cutting edges. The wood contains silica deposits as well as natural resin, causing a high blunting effect on standard steel blades. Workshop builders should utilize stellite-tipped saw teeth for ripping and crosscutting, alongside tungsten carbide knives and router bits for flattening slabs and shaping tabletop edges. While slicing performance is graded as good for veneer, rotary peeling is not recommended.
What fastening and assembly requirements apply to Rengas?
Mechanical fastening in Rengas is rated as good for both screws and nails, but pre-boring is strictly necessary to avoid splitting the timber. In terms of mechanical strength, Rengas tests at 49 MPa (about 7,110 psi) in crushing strength, 85 MPa (about 12,330 psi) in static bending strength, and possesses a modulus of elasticity of 18,500 MPa (about 2,683,000 psi).
Woodworkers handling Rengas must take careful health precautions. CIRAD Tropix notes that Rengas contains silica deposits, allergenic deposit contents, and poisonous resin exudations. Proper shop ventilation, dust extraction, skin protection, and standard epoxy edge preparation per your resin manufacturer’s instructions are essential during handling and assembly.
What are the natural durability classes and CITES status?
The natural durability of Rengas heartwood places it in Use Class 2, defined as inside or under cover where dampness is possible. Its biological resistance is categorized as:
- Fungi (decay): Durability class 3 (moderately durable)
- Dry-wood borers: Class S (susceptible across all wood)
- Termites: Class M (moderately durable)
- Treatability: Class 3-4 (poorly or not permeable)
Because dry-wood borers pose an active risk, appropriate preservative treatments are required where exposure exists. Common listed end-uses include cabinetwork for high-class furniture, indoor staircases, flooring, interior panelling, seats, sculpture, turned goods, wood-ware, and sliced veneer. Rengas is not listed in the CITES Appendices (Washington Convention 2025).
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: The CIRAD Tropix sheet documents that Rengas timber possesses a thermal conductivity (λ) of 0.23 W/(m·K), reflecting typical heat-insulating characteristics common to moderately dense tropical hardwoods. (Source: CIRAD Tropix 7 technical sheet: Rengas.)