Pau Mulato as a Wood for Epoxy River Tables
Pau mulato (Calycophyllum spruceanum) is a dense hardwood from Latin America, sourced from countries such as Argentina, Bolivia, Brazil, Ecuador, Paraguay, and Peru. Documented in the CIRAD Tropix technical sheet, this timber presents a clean, refined appearance and exceptional mechanical stiffness, making it an intriguing candidate for high-end epoxy river tables and solid tabletops.
Visual Characteristics and Figure
The CIRAD Tropix data lists the wood color reference as yellow brown, with notes clarifying that it ranges from beige grey to uniform yellowish beige. The sapwood is not demarcated from the heartwood. It features a fine texture and grain that is straight or interlocked, with interlocked grain described as slight. On quarter sawn faces, the wood displays a very fine but perceptible silver figure, offering subtle depth next to tinted or clear epoxy resin channels.
Density, Hardness, and Mechanical Strength
Pau mulato is a heavy wood. At 12% moisture content, it has an average specific gravity of 0.83, which equals roughly 51.8 lb/ft³. For a 2-inch-thick slab, that results in a weight of about 8.6 lb per sq ft. Its mechanical ratings from the CIRAD Tropix sheet show immense rigidity and crush resistance, with a crushing strength of 77 MPa (about 11,170 psi), a static bending strength of 116 MPa (about 16,820 psi), and a modulus of elasticity of 20,560 MPa (about 2,982,000 psi).
Its hardness is rated on the French Monnin scale at 6.5. The Monnin hardness test measures the depth of an indentation under controlled force, where a higher score signifies a harder surface. Monnin is entirely separate from the North American Janka test and cannot be directly converted into Janka pounds, but a score of 6.5 indicates a tough surface that resists tabletop dings.
Shrinkage and Movement Along Epoxy Rivers
When embedding wood slabs alongside rigid epoxy, shrinkage behavior dictates long-term stability. The CIRAD Tropix technical data records a total tangential shrinkage of 8.2 % and a total radial shrinkage of 3.9 %, yielding an St/Sr ratio of 2.1. The fibre saturation point is 22 %, and the coefficient of volumetric shrinkage is 0.55 % per % MC.
An St/Sr ratio of 2.1 indicates a moderate tendency to cup if moisture shifts occur across flatsawn faces. Because Pau mulato is dense and shrinks 8.2 % tangentially from green to oven-dry, any unsealed slab undergoing seasonal humidity changes will exert strong shear forces on the resin seam. Slabs must be equilibrated to indoor conditions before resin casting.
Drying Behavior and Kiln Risks
The CIRAD Tropix sheet notes that air drying prior to kiln drying is recommended. When seasoned, the risk of distortion is rated as slight, and the risk of checking is slight. Collapse and casehardening both carry no known specific risk. Suggested kiln drying schedules run from 53 to 65 °C (about 127 to 149 °F), calling for gradual reductions in relative humidity to safely extract core moisture.
Machining and Gluing Notes
Despite its density, the blunting effect on tools is described as normal. However, CIRAD recommends stellite-tipped saw teeth and tungsten carbide cutting tools to handle production runs cleanly. For fastening, nailing and screwing properties are good, but pre-boring is necessary to avoid splitting.
Regarding assembly and adhesion, the CIRAD Tropix notes state: High specific gravity: gluing must be especially performed in compliance with the code of practice. In an epoxy shop, this requires clean joint preparation, thorough dust removal, and careful attention to epoxy manufacturer bonding instructions.
Durability and Trade Status
Pau mulato heartwood is rated as durability class 3 (moderately durable) against xylophagous fungi and class M (moderately durable) against termites. However, it is class S (susceptible) to dry-wood borers with risk throughout the wood. Heartwood treatability is class 3 (poorly permeable). Its natural durability corresponds to use class 2 (interior or under cover, where dampness is possible). The species is not listed in the CITES Appendices under the Washington Convention 2025.
Common end-uses recorded in CIRAD include cabinetwork for high-class furniture, flooring, interior joinery, musical instruments, sculpture, tool handles, turned goods, and wood-ware.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Calycophyllum spruceanum | |
| Colour / texture / grain | Yellow brown; texture fine; grain straight or interlocked; interlocked grain slight | |
| Specific gravity (12% MC) | 0.83 | about 51.8 lb/ft³; a 2-inch-thick slab weighs about 8.6 lb per sq ft |
| Monnin hardness (12% MC) | 6.5 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 8.2 % | green to oven-dry |
| Total radial shrinkage | 3.9 % | green to oven-dry |
| Ratio St/Sr | 2.1 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.55 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 22 % | |
| Thermal conductivity | 0.27 W/(m·K) | |
| Crushing strength (12% MC) | 77 MPa | about 11,170 psi |
| Static bending strength (12% MC) | 116 MPa | about 16,820 psi |
| Modulus of elasticity (12% MC) | 20,560 MPa | about 2,982,000 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 – poorly permeable | |
| Use class from natural durability | Class 2 – inside or under cover (dampness possible) | |
| Drying | rate no information available; distortion: 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 normal; 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).
Practical Pre-Pour Checklist for Pau Mulato
- Verify that the timber is acclimated to interior relative humidity before casting, as the 0.55 % per % MC volumetric shrinkage rate will stress the epoxy bond if moisture fluctuates.
- Flatten boards with carbide tooling to ensure clean surfaces and prevent tear-out along zones of interlocked grain.
- Clean the live-edge river walls thoroughly to remove loose fibers and mill dust before applying a seal coat.
- Pre-bore all pilot holes for table base mounting screws, as the 0.83 specific gravity makes mechanical fasteners prone to binding or splitting the timber.
- Design the table exclusively for interior use, aligning with the species use class 2 rating.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: Log diameters for Pau mulato generally range from 30 to 40 cm, meaning wide river tabletops will typically require edge-glued board panels or narrower bookmatched slabs rather than giant single-slab tops. (Source: CIRAD Tropix 7 technical sheet: Pau mulato.)