An Introduction to Cupiuba for Epoxy Tabletops
Cupiuba (Goupia glabra) is a Latin American hardwood documented in the technical publications of CIRAD Tropix. Originating from trees with log diameters typically ranging from 60 to 100 cm, it yields substantial lumber and slabs suitable for large furniture commissions. While its strength and density make it a robust candidate for heavy-duty applications, building an epoxy river table or hybrid tabletop with Cupiuba requires a clear understanding of its physical movement, drying quirks, and working characteristics.
Appearance, Figure, and Distinct Odor
The heartwood of Cupiuba displays a consistent yellow brown coloration. Its sapwood is clearly demarcated from the heartwood, forming an outer band between 3 and 8 cm thick. The wood exhibits a medium texture and an interlocked grain that is marked but not frequent. Builders planning live-edge epoxy pours will appreciate the distinct contrast between heartwood and sapwood. However, CIRAD Tropix notes that the wood possesses an unpleasant odour, which can limit its use if not properly managed, and internal stresses are sometimes present in the timber.
Weight, Hardness, and Structural Strength
Cupiuba is a heavy, dense timber. At 12% moisture content, it has an average specific gravity of 0.84, which translates to a density of roughly 52.4 lb/ft³. In practical tabletop terms, a planed 2-inch-thick slab weighs approximately 8.7 lb per square foot before epoxy is cast. Sturdy table bases and solid joinery are essential to support this mass.
On the French Monnin hardness scale, Cupiuba measures 6.2 at 12% moisture content. The Monnin scale measures surface resistance where a higher number indicates a harder material; it is not a Janka value and should not be treated as one. Paired with this surface hardness is remarkable structural strength: Cupiuba records a crushing strength of 62 MPa (about 8,990 psi), a static bending strength of 110 MPa (about 15,950 psi), and a modulus of elasticity of 18,190 MPa (about 2,638,000 psi). For long dining tables or unsupported spans, slab deflection under load is minimal.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Goupia glabra | |
| Colour / texture / grain | Yellow brown; texture medium; grain interlocked; interlocked grain marked but not frequent | |
| Specific gravity (12% MC) | 0.84 | about 52.4 lb/ft³; a 2-inch-thick slab weighs about 8.7 lb per sq ft |
| Monnin hardness (12% MC) | 6.2 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 8.8 % | green to oven-dry |
| Total radial shrinkage | 5.1 % | green to oven-dry |
| Ratio St/Sr | 1.7 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.66 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 26 % | |
| Thermal conductivity | 0.27 W/(m·K) | |
| Crushing strength (12% MC) | 62 MPa | about 8,990 psi |
| Static bending strength (12% MC) | 110 MPa | about 15,950 psi |
| Modulus of elasticity (12% MC) | 18,190 MPa | about 2,638,000 psi |
| Decay (fungi) resistance | Durability class 3 – moderately durable | |
| Termite resistance | Class D – durable | |
| Dry-wood borer resistance | Class D – durable (sapwood demarcated, risk limited | |
| Heartwood treatability | Class 2 – moderately permeable | |
| Use class from natural durability | Class 2 – inside or under cover (dampness possible) | |
| Drying | rate slow; distortion: high risk; checking: high risk; collapse: no known specific risk; casehardening: yes | |
| Suggested kiln program temperatures | 53–65 °C | about 127–149 °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).
Shrinkage and Stability Next to an Epoxy River
Whenever wood is permanently bonded to epoxy resin, movement differentials can induce extreme stress along the glue line. Cupiuba shows a total tangential shrinkage of 8.8% and a total radial shrinkage of 5.1% from green to oven-dry, yielding an St/Sr ratio of 1.7. Its coefficient of volumetric shrinkage is 0.66% per 1% change in moisture content, with a fibre saturation point of 26%.
A volumetric shrinkage coefficient of 0.66% indicates moderate-to-high dimensional movement in response to seasonal humidity shifts. The 1.7 shrinkage ratio indicates a moderate tendency toward cupping. When paired with an unyielding epoxy river, any substantial change in shop or home moisture can place significant shear stress on the resin-to-wood interface. Slabs must be thoroughly acclimated and dried down to interior equilibrium before resin casting.
Drying Risks and Kiln Behavior
Drying Cupiuba requires caution. CIRAD Tropix rates its drying rate as slow and highlights a high risk of distortion as well as a high risk of checking. Casehardening is also documented as a risk, though there is no known specific risk of collapse. Because drying must proceed slowly to avoid severe checking and twist, kiln schedules utilize mild temperatures, starting at 53 °C (about 127 °F) and reaching up to 65 °C (about 149 °F) during the final stages. Attempting to force-dry Cupiuba slabs rapidly will almost certainly trigger deep face checks that require extensive epoxy filling.
Machining, Gluing, and Finishing Considerations
Working Cupiuba presents distinct shop challenges:
- Tool wear: Cupiuba has a fairly high blunting effect on cutters. CIRAD Tropix recommends stellite-tipped saw teeth and tungsten carbide cutting knives.
- Surfacing: Because the wood contains interlocked grain, careful sanding is necessary to achieve a uniform, tearout-free surface.
- Fasteners: Pre-boring is strictly necessary for screws and nails to avoid splitting.
- Gluing: Because of the wood’s high specific gravity (0.84), CIRAD Tropix notes that gluing must be performed in strict compliance with the code of practice. For epoxy pours, surfaces along the river chasm should be freshly prepped, scuffed, and cleaned in line with standard adhesive guidelines.
- Finishing: CIRAD notes that filling and varnishing are necessary for furniture end-uses. A comprehensive film finish also encapsulates the wood to contain its unpleasant natural scent.
Natural Durability and CITES Status
In terms of biological resistance, Cupiuba heartwood is rated Durability class 3 (moderately durable) against xylophagous fungi, while ranking as durable (Class D) against termites and dry wood borers. Heartwood treatability is Class 2 (moderately permeable), and its natural durability places it in Use Class 2 (interior or under cover, dampness possible). According to CIRAD Tropix, Cupiuba is not listed in the CITES Appendices (Washington Convention 2025). Documented end-uses include current furniture or furniture components, flooring, industrial flooring, indoor staircases, exterior joinery and panelling, heavy carpentry, wood frame housing, sliced veneer, and turned goods.
Is Cupiuba a Good Epoxy Table Wood?
Cupiuba can serve well in epoxy river tables, but it is an exacting species. Its warm yellow brown color, distinct sapwood, high density, and Monnin hardness of 6.2 create a rugged, wear-resistant tabletop. However, builders must respect its high risk of checking and distortion during drying, its fairly high tool blunting, and its 0.66% volumetric movement. Thorough drying, slow conditioning, careful sanding of its interlocked grain, and complete topcoat sealing to contain its natural odor are mandatory steps for a successful build.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: According to the CIRAD Tropix sheet’s reference to European standard NF EN 350 (2016), Cupiuba heartwood has good to very good resistance specifically against brown cubical rot, but only moderate resistance against white rot. (Source: CIRAD Tropix 7 technical sheet: Cupiuba.)