Working with Douka in Epoxy River Tables
Douka (Tieghemella africana) is a dense African hardwood known for its rich coloration, fine working qualities in high-class furniture, and remarkable stability. For custom epoxy river tables and composite tabletops, Douka offers favorable dimensional behavior and striking figure. However, its physical density, high silica content, and international trade restrictions require close attention during design and prep. All technical figures referenced here originate from the CIRAD Tropix technical sheet for Douka.
Appearance, Grain, and Slab Dimensions
The heartwood of Douka ranges from dark pinkish brown to dark reddish brown, often featuring purplish glints or subtle, indistinct pale veins. The wood frequently exhibits a moiré figure, bringing deep visual movement beneath a clear epoxy flood coat or penetrating tabletop finish. The grain is straight or interlocked, though interlocked grain is described as marked but not frequent. Its texture is medium.
Douka logs range from 90 to 150 cm in diameter, meaning sawyers can produce wide, single-slab boards capable of spanning entire dining tables or river tabletop halves without excessive edge-gluing. The sapwood is clearly demarcated from the heartwood, displaying a whitish to pinkish tone with a thickness ranging from 4 to 8 cm.
Weight, Monnin Hardness, and Mechanical Strength
Douka is a heavy hardwood with a specific gravity of 0.72 at 12% moisture content. In workshop terms, this translates to a density of about 44.9 lb/ft³, meaning a 2-inch-thick slab weighs approximately 7.5 lb per sq ft. Builders should design table legs, aprons, and metal bases capable of carrying significant overall mass.
Surface hardness is measured at 4.2 on the Monnin scale. Monnin hardness is a standardized French test where a higher number denotes a harder timber; it should not be converted to or confused with Janka hardness. A Monnin rating of 4.2 places Douka in a solid, wear-resistant bracket suitable for dining tables, flooring, and interior staircases. Structurally, Douka delivers a crushing strength of 62 MPa (about 8,990 psi), a static bending strength of 105 MPa (about 15,230 psi), and a modulus of elasticity of 14,600 MPa (about 2,118,000 psi).
Shrinkage and River Table Stability
When pairing solid lumber with rigid epoxy casting resins, differential movement is the primary cause of tabletop failure. Douka displays excellent stability ratios. Its total tangential shrinkage is 6.9%, while total radial shrinkage is 5.3%. This produces a tangential-to-radial shrinkage ratio of 1.3. A ratio close to 1 indicates uniform dimensional behavior across plain-sawn and quarter-sawn surfaces, significantly lowering the risk of cupping or lateral stress against the resin river.
Douka features a fibre saturation point of 27% and a coefficient of volumetric shrinkage of 0.45% per 1% change in moisture content. Once dried thoroughly below its fibre saturation point, seasonal movement remains moderate, minimizing tension across the cured epoxy bondline.
Drying Behavior and Risks
According to the CIRAD Tropix research, Douka exhibits a normal drying rate. The material poses only a slight risk of checking and a slight risk of distortion. Furthermore, CIRAD reports no known specific risk for collapse or casehardening. For kiln drying, suggested drying schedules utilize temperatures between 55 and 65 °C (about 131 to 149 °F).
Tool Wear, Pre-Boring, and Natural Durability
Douka possesses a high blunting effect on tools due to its high silica content. Standard carbon steel blades dull quickly; woodworkers must employ stellite-tipped saw teeth and tungsten carbide cutting edges on jointers, planers, and router surfacing sleds. Fastener holding is good, but pre-boring is necessary to prevent splitting when mounting leg plates or threaded inserts.
Douka heartwood is highly durable. It holds Durability class 1 (very durable) against wood-decay fungi and Class D (durable) against termites and dry-wood borers. Its heartwood treatability is Class 4 (not permeable), meaning it does not readily absorb chemical preservatives. It naturally fulfills Use Class 4 (in ground or fresh water contact) and European Use Class 5 for marine submersion due to its silica.
CITES and Legal Regulations
Douka is not listed in the CITES Appendices (Washington Convention 2025). However, strict regional felling bans exist. In Gabon, decree n°137/PR/MEFEPA of February 4, 2009 prohibited felling Douka for 25 years, classifying it as non-exploitable and non-marketable through December 31, 2033. Slabs should only be sourced with clear documentation verifying legal provenance outside restricted zones.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Tieghemella africana | |
| Colour / texture / grain | Red brown; texture medium; grain straight or interlocked; interlocked grain marked but not frequent | |
| Specific gravity (12% MC) | 0.72 | about 44.9 lb/ft³; a 2-inch-thick slab weighs about 7.5 lb per sq ft |
| Monnin hardness (12% MC) | 4.2 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 6.9 % | green to oven-dry |
| Total radial shrinkage | 5.3 % | green to oven-dry |
| Ratio St/Sr | 1.3 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.45 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 27 % | |
| Thermal conductivity | 0.24 W/(m·K) | |
| Crushing strength (12% MC) | 62 MPa | about 8,990 psi |
| Static bending strength (12% MC) | 105 MPa | about 15,230 psi |
| Modulus of elasticity (12% MC) | 14,600 MPa | about 2,118,000 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 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 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). Notes. In Gabon, according to decree n°137/PR/MEFEPA of February 4, 2009, Douka is prohibited from felling, classified as non-exploitable and non-marketable since January 1, 2009, and this for 25 years, i.e. until December 31, 2033. It is forbidden to cut, saw, transport or sell the wood of this species. However, in the context of the exercise of customary use rights by village communities, this legal provision does not prevent the harvesting of fruit, bark, latex or resin according to Decree No. 692/PR/MEFEPEPN of 24 August 2004. |
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).
Practical Pre-Pour Checklist for Douka River Tables
- Verify slab provenance to ensure the wood does not violate regional felling bans, such as Gabon’s 25-year moratorium running until December 31, 2033.
- Inspect moisture levels throughout the slab core, ensuring the lumber has completed drying well below its 27% fibre saturation point.
- Examine the 4 to 8 cm sapwood band; while heartwood is Class D durable, dry-wood borer risk is limited to the sapwood, requiring careful inspection before casting.
- Surface the slab using sharp tungsten carbide tooling to avoid tearout along areas of interlocked or moiré grain.
- Thoroughly clean all fine silica and machining dust from the live edges to avoid weak spots along the resin boundary.
- Apply an epoxy seal coat along the live edges per the resin manufacturer’s data sheet to seal the medium-textured pores and eliminate outgassing bubbles.
- Pre-drill all fastener pilot holes on the tabletop underside before driving screws or installing inserts.
Sources
Published October 31, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: Because the CIRAD data sheet notes that dry-wood borer risk is strictly limited to the 4 to 8 cm sapwood band while the heartwood remains Class D durable, builders leaving live edges on Douka slabs should carefully probe the sapwood for entry holes or consider trimming it away entirely before pouring resin. (Source: CIRAD Tropix 7 technical sheet: Douka.)