Working with Okan in Epoxy River Tables
Okan (Cylicodiscus gabunensis) is an exceptionally heavy African hardwood sourced from countries such as Cameroon, Gabon, Ghana, and Nigeria. Reaching trunk diameters between 90 and 150 cm with a sapwood band of 5 to 8 cm, this species produces broad slabs suitable for river tables and structural wood tops. According to the CIRAD Tropix technical sheet, Okan is not listed in the CITES Appendices (Washington Convention 2025), making it a commercially viable alternative to species like azobe and greenheart.
When green, the timber carries an unpleasant odour, and its heartwood shifts from yellow brown to a deep red brown once exposed to air. The sapwood is clearly demarcated from the heartwood. Okan features a medium texture and marked interlocked grain, which presents unique visual character as well as specific mechanical challenges when preparing live-edge slabs for resin casting.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Cylicodiscus gabunensis | |
| Colour / texture / grain | Red brown; texture medium; grain interlocked; interlocked grain marked | |
| Specific gravity (12% MC) | 0.91 | about 56.8 lb/ft³; a 2-inch-thick slab weighs about 9.5 lb per sq ft |
| Monnin hardness (12% MC) | 10.3 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 7.9 % | green to oven-dry |
| Total radial shrinkage | 5.8 % | green to oven-dry |
| Ratio St/Sr | 1.4 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.61 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 25 % | |
| Thermal conductivity | 0.29 W/(m·K) | |
| Crushing strength (12% MC) | 82 MPa | about 11,890 psi |
| Static bending strength (12% MC) | 134 MPa | about 19,440 psi |
| Modulus of elasticity (12% MC) | 22,260 MPa | about 3,229,000 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: high 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).
Density, Hardness, and Mechanical Strength
Okan is an exceptionally dense timber. At 12% moisture content, it has an average specific gravity of 0.91, corresponding to a density of approximately 56.8 lb/ft³. In the shop, this translates to a 2-inch-thick slab weighing roughly 9.5 lb per square foot. Table bases and hardware must be engineered to handle this significant mass.
The wood measures 10.3 on the Monnin hardness scale at 12% moisture content. The Monnin scale is an established French testing metric where higher numbers denote harder timber; it should not be confused with or converted into Janka values. Okan also demonstrates immense structural rigidity, with a modulus of elasticity of 22,260 MPa (about 3,229,000 psi), a static bending strength of 134 MPa (about 19,440 psi), and a crushing strength of 82 MPa (about 11,890 psi). These metrics explain why CIRAD lists heavy industrial flooring, bridges, vehicle flooring, and marine hydraulic works among its traditional end-uses.
Shrinkage, Drying Risks, and Epoxy Interface Stability
The boundary between cured epoxy resin and natural timber is vulnerable to seasonal dimensional change. Okan has a fibre saturation point of 25%, with total tangential shrinkage measured at 7.9% and total radial shrinkage at 5.8%. Its ratio of tangential to radial shrinkage is 1.4, which indicates a moderate tendency to cup compared to less balanced species. However, its coefficient of volumetric shrinkage is 0.61% per 1% change in moisture content.
CIRAD records that Okan has a slow drying rate, accompanied by a high risk of distortion and a high risk of checking. Fortunately, there is no known specific risk of collapse or casehardening. Recommended kiln schedules suggest temperatures between 45 and 65 °C (113 and 149 °F). Slabs must be brought to full equilibrium with your shop environment before casting; bonding unconditioned Okan against rigid epoxy invites severe internal stress, checking, or edge delamination as the timber slowly reaches moisture stability.
Machining, Gluing, and Natural Durability
Shaping and surfacing Okan requires dedicated tooling. The timber exerts a fairly high blunting effect on cutting edges. CIRAD recommends stellite-tipped saw teeth and tungsten carbide knives or router bits. Due to marked interlocked grain, quartersawn surfaces show a distinct tendency to tear out during planing or jointing, demanding light passes and careful feed speeds to obtain a clean finish.
For fasteners, screwing and nailing hold well, but pre-boring is strictly necessary to prevent splitting in such a hard wood. CIRAD notes that due to Okan’s high specific gravity, gluing must be performed in strict compliance with the code of practice. Heartwood treatability is classified as Class 4 (not permeable), meaning deep epoxy penetration into raw edge fibers is limited. Live edges should be thoroughly surfaced and clean before resin contact.
Okan is naturally resilient, rated as Durability class 1 (very durable against decay fungi) and Class D (durable against termites and dry-wood borers). Its natural durability satisfies use class 4 (in ground or fresh water contact) and naturally covers use class 5 (marine submersion) per European standard NF EN 350. However, the sheet warns of a risk of staining or dripping caused by the leaching of water-soluble, colored chemical compounds such as tannins, which can bleed into surrounding structures if exposed to moisture.
Pre-Pour Checklist for Okan Slabs
- Confirm Moisture Equilibrium: Ensure the slab has slowly dried past its 25% fibre saturation point and fully acclimated to target interior relative humidity.
- Check for Surface Checks: Inspect the slab faces thoroughly for drying checks and micro-fractures associated with Okan’s high checking risk.
- Debark and Profile the Edges: Remove all sapwood bark, inspect the 5 to 8 cm demarcated sapwood zone, and clean the live edges thoroughly.
- Tool with Carbide Cutters: Surface the slab faces using sharp tungsten carbide cutters, taking light passes to minimize grain tearout on quartersawn figure.
- Pre-Bore All Mechanical Fasteners: Drill clearance holes for all mounting hardware, C-channels, or threaded inserts to avoid splitting the 10.3 Monnin heartwood.
- Mitigate Chemical Bleed: Seal the timber thoroughly to lock in water-soluble extractives and tannins before casting resin or applying topcoats.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: CIRAD Tropix indicates that Okan carries an unpleasant odour when green and presents a risk of leaching water-soluble chemical compounds like tannins, making thorough pre-sealing critical to prevent discoloration around the cast resin. (Source: CIRAD Tropix 7 technical sheet: Okan.)