Working with Black Guarea in Epoxy River Tables
Guarea, Black*—also known by the commercial trade name Bossé foncé (*Guarea thompsonii*)—is an African hardwood belonging to the Meliaceae family. Renowned for its service in high-class cabinetwork, interior and exterior joinery, cigar boxes, and boat decking, this timber provides a distinct alternative to standard furniture hardwoods. When pairing wide timber slabs with cast epoxy resin, understanding wood behavior under moisture and stress is critical. According to the CIRAD Tropix technical sheet for Guarea, Black* / Bossé foncé, this species combines notable mechanical stiffness with specific shop-handling requirements that every custom tabletop maker should evaluate.
Appearance, Figure, and Wood Characteristics
Black Guarea timber displays a rich orange brown heartwood offset by clearly demarcated sapwood measuring between 5 to 10 cm thick. The grain is interlocked, described by CIRAD as marked and irregular, yet straighter than that of scented Guarea. When surfaced, the interlocked grain often creates a slightly moiré appearance across the slab faces, backed by a fine overall texture. Log diameters typically range from 60 to 80 cm, yielding moderate slab widths suited for two-piece river table builds or multi-board laminated table designs.
Shop workers should also note an aromatic characteristic: the wood possesses a strong unpleasant odour that may persist after the timber has dried.
Density, Strength, and Hardness
At 12% moisture content, Black Guarea has a specific gravity of 0.68, which corresponds to an average density of approximately 42.5 lb/ft³. For river table fabrication, a 2-inch-thick slab weighs approximately 7.1 lb per square foot before epoxy is cast. Its crushing strength measures 66 MPa (about 9,570 psi), and its static bending strength reaches 116 MPa (about 16,820 psi), with a modulus of elasticity of 15,600 MPa (about 2,263,000 psi).
Rather than using the American Janka test, CIRAD measures indentation resistance with the French Monnin hardness test. On this scale, higher numbers reflect harder wood. Black Guarea tests at a Monnin hardness of 5.3 at 12% moisture content. This solid hardness gives finished tabletops good surface resistance against routine wear, though it also impacts how the wood behaves under cutting tools and fasteners.
Shrinkage, Stability, and the Epoxy River Joint
Because cured epoxy resin is completely rigid and does not shrink or expand with seasonal humidity, pairing it with wood requires examining shrinkage coefficients:
- Total tangential shrinkage: 7.0 %
- Total radial shrinkage: 4.4 %
- Shrinkage ratio (St/Sr): 1.6
- Volumetric shrinkage coefficient: 0.43 % per % MC
- Fibre saturation point: 26 %
An St/Sr ratio of 1.6 indicates a moderate, relatively balanced relationship between tangential and radial movement, pointing to a lower tendency to cup or twist compared to woods with extreme differential ratios. The volumetric movement of 0.43% per percentage change in moisture content means the boards must be thoroughly dried and acclimated to the destination environment before casting, preventing stress concentrations along the resin bondline.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Guarea thompsonii | |
| Colour / texture / grain | Orange brown; texture fine; grain interlocked; interlocked grain marked | |
| Specific gravity (12% MC) | 0.68 | about 42.5 lb/ft³; a 2-inch-thick slab weighs about 7.1 lb per sq ft |
| Monnin hardness (12% MC) | 5.3 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 7.0 % | green to oven-dry |
| Total radial shrinkage | 4.4 % | green to oven-dry |
| Ratio St/Sr | 1.6 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.43 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 26 % | |
| Thermal conductivity | 0.23 W/(m·K) | |
| Crushing strength (12% MC) | 66 MPa | about 9,570 psi |
| Static bending strength (12% MC) | 116 MPa | about 16,820 psi |
| Modulus of elasticity (12% MC) | 15,600 MPa | about 2,263,000 psi |
| Decay (fungi) resistance | Durability class 2 – durable | |
| Termite resistance | Class S – susceptible | |
| Dry-wood borer resistance | Class D – durable (sapwood demarcated, risk limited | |
| Heartwood treatability | Class 4 – not permeable | |
| Use class from natural durability | Class 3 – not in ground contact, outside | |
| Drying | rate rapid to normal; distortion: slight risk; checking: slight risk; collapse: no known specific risk; casehardening: no known specific risk | |
| Suggested kiln program temperatures | 55–65 °C | about 131–149 °F |
| Machining | blunting fairly high; saw teeth: stellite-tipped; cutting tools: tungsten carbide | |
| Nailing and screwing | Good | |
| CITES status | This species is not listed in the CITES Appendices (Washington Convention 2025). Notes. * Common commercial name |
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 for Epoxy Tabletops
Pros
- Attractive Figure: Orange brown coloration with fine texture and a slightly moiré pattern caused by marked interlocked grain.
- Favorable Movement Ratio: A 1.6 tangential-to-radial shrinkage ratio limits severe cupping forces alongside cast epoxy channels.
- Solid Tabletop Strength: Crushing strength of 66 MPa and static bending strength of 116 MPa resist denting and tabletop deflection.
- Heartwood Durability: Ranked as Durability Class 2 (durable) against fungi and Class D (durable) against dry-wood borers.
- CITES Unregulated: Not listed in the CITES Appendices (Washington Convention 2025).
Cons
- Fairly High Tool Wear: Blunting effect requires specialized stellite-tipped saws and tungsten carbide cutters.
- Persistent Odour: Carries a strong, unpleasant smell that can remain noticeable even after the wood is fully seasoned.
- Respiratory Irritant: Sawdust produced during milling, routing, and sanding is classified as an irritant.
- Termite Susceptibility: Heartwood is classified as Class S (susceptible) to termites.
- Impermeable Heartwood: Treatability is Class 4 (not permeable), limiting chemical preservative uptake.
Build Notes for the Epoxy Shop
Slab Selection
Logs range from 60 to 80 cm in diameter, making them suitable for bookmatched slabs or river arrangements. Inspect the live edges carefully: the sapwood is clearly demarcated and 5 to 10 cm thick. While the heartwood is Class D durable against dry-wood borers, the sapwood carries borer risk; remove any damaged or punky sapwood before laying slabs into the pour mold.
Drying Slabs
CIRAD notes that Black Guarea dries at a rapid to normal rate. The drying process carries only a slight risk of distortion and a slight risk of checking, with no known specific risk of collapse or casehardening. Standard industrial kiln schedules for the species operate with temperatures between 55 °C and 65 °C (131 °F to 149 °F).
Machining and Fastening
The timber causes fairly high tool blunting. Use tungsten carbide cutting knives and stellite-tipped saw teeth to maintain clean cuts and avoid surface burnishing. Interlocked grain demands sharp cutters to avoid tearout during jointing and planing. Nailing and screwing properties are rated as good, though pre-boring is recommended due to the wood’s density and Monnin hardness. Effective dust collection and protective respirators are mandatory because the fine sawdust is a known irritant.
Sealing and Bonding
Because Black Guarea heartwood is Class 4 (not permeable), deep penetration of low-viscosity sealers is naturally limited. Scuff-sand the river edges thoroughly with clean, sharp abrasives to clear any glaze, and follow the resin manufacturer’s directions by applying a thin seal coat before the deep pour to lock the pores and prevent trapped outgassing bubbles.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: When attaching heavy metal table bases to Black Guarea slabs, always pre-bore pilot holes for threaded inserts or lag bolts; driving screws directly into this wood risks head shear due to its 5.3 Monnin hardness and 66 MPa crushing strength. (Source: CIRAD Tropix 7 technical sheet: Black Guarea (Bossé Foncé).)