Brown Sterculia Spec-Sheet Summary for Table Builders
Brown sterculia (Sterculia rhinopetala) is an African hardwood harvested primarily in Cameroon, Côte d’Ivoire, Ghana, and Nigeria. Documented in the CIRAD Tropix technical sheet, this timber produces heartwood with a distinct red brown colour, clearly demarcated from sapwood that measures from 4 to 6 cm in thickness. The wood exhibits a coarse texture and grain that runs straight or interlocked, with the interlocked grain categorized as slight. Typical log diameters range from 60 to 80 cm, providing modest to medium widths suitable for bookmatched table slabs, multi-board table tops, or river table layouts flanked by a central resin cast.
In terms of weight and strength, Brown sterculia is a dense, robust species. It presents a specific gravity of 0.84 at 12% moisture content, translating to a density of about 52.4 lb/ft³. A 2-inch-thick slab weighs about 8.7 lb per sq ft, requiring sturdy structural bases and proper support frames. Its mechanical baseline includes a crushing strength of 72 MPa (about 10,440 psi), a static bending strength of 133 MPa (about 19,290 psi), and a modulus of elasticity of 18,670 MPa (about 2,708,000 psi). For surface resistance, the species registers a Monnin hardness of 5.6. The Monnin scale is a French hardness measurement where higher values designate harder timber; it should not be converted to a Janka rating.
Dimensional movement requires disciplined shop practices when designing wood and epoxy assemblies. Brown sterculia possesses a total tangential shrinkage of 10.0% and a total radial shrinkage of 5.0%, yielding a tangential-to-radial shrinkage ratio of 2.0. Its coefficient of volumetric shrinkage is 0.68% per % MC, with a fibre saturation point of 26%. Because the drying rate is slow and carries a high risk of distortion as well as a high risk of checking, raw slabs demand careful conditioning prior to resin work. CIRAD notes quartersawn lumber is recommended to minimize defect development. At the resin bondline, high movement values mean any moisture swing after casting can exert significant stress against the epoxy interface.
Working this timber involves standard tooling but specific shop hygiene. Tool blunting is normal, permitting the use of ordinary cutting tools and saw teeth made of ordinary or alloy steel. However, the sawdust is classified as very irritant, and slight interlocked grain can cause some difficulties in planing. Fastener installation demands pre-boring because the timber tends to split when nailed. Because of the high specific gravity, CIRAD notes that gluing must be performed in compliance with the code of practice, followed by the resin manufacturer’s directions. For final finishing, grain filling is recommended to achieve a smooth, even surface over the coarse texture.
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Sterculia rhinopetala | |
| Colour / texture / grain | Red brown; texture coarse; grain straight or interlocked; interlocked grain slight | |
| 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) | 5.6 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 10.0 % | green to oven-dry |
| Total radial shrinkage | 5.0 % | green to oven-dry |
| Ratio St/Sr | 2.0 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.68 % 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) | 72 MPa | about 10,440 psi |
| Static bending strength (12% MC) | 133 MPa | about 19,290 psi |
| Modulus of elasticity (12% MC) | 18,670 MPa | about 2,708,000 psi |
| Decay (fungi) resistance | Durability class 2 – durable | |
| Termite resistance | Class M – moderately durable | |
| Dry-wood borer resistance | Class D – durable (sapwood demarcated, risk limited | |
| Heartwood treatability | Class 3 – poorly 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: no known specific risk | |
| Suggested kiln program temperatures | 53–65 °C | about 127–149 °F |
| Machining | blunting normal; saw teeth: ordinary or alloy steel; cutting tools: ordinary | |
| 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).
Frequently Asked Questions
What slab widths are possible with Brown sterculia?
According to CIRAD Tropix data, log diameters for Sterculia rhinopetala typically range from 60 to 80 cm. Because sapwood measures from 4 to 6 cm thick on the edges, builders working with single live-edge slabs will generally yield medium widths. Wide dining tabletops often require two bookmatched slabs or an epoxy river design spanning between two live-edge boards.
What does a Monnin hardness of 5.6 mean for a tabletop?
Monnin hardness is an established French test metric where higher numbers indicate greater resistance to indentation; it is not a Janka score and cannot be converted to one. A Monnin rating of 5.6 reflects a firm, solid surface well-suited for heavy-use applications such as furniture components, flooring, indoor staircases, and tabletops.
How should builders handle the high shrinkage and drying risks?
Brown sterculia has a high risk of checking and a high risk of distortion, paired with a slow drying rate. The total tangential shrinkage of 10.0% and radial shrinkage of 5.0% (ratio of 2.0) mean unseasoned boards will distort readily. CIRAD recommends quartersawn material to reduce drying defects. Kiln schedules suggested by CIRAD operate within temperatures of 53 to 65 °C (about 127 to 149 °F) to gently bring the wood down to indoor targets before casting epoxy.
How does the high specific gravity affect epoxy gluing and river joins?
With a specific gravity of 0.84, Brown sterculia is a dense wood. CIRAD emphasizes that gluing must especially follow proper codes of practice due to this density. Wood surfaces should be cleanly prepped, free of loose debris, and cast strictly within moisture equilibrium so expansion or contraction does not strain the wood-epoxy boundary.
What workshop health precautions are required when machining this wood?
The CIRAD Tropix sheet explicitly highlights that Brown sterculia creates very irritant sawdust. Woodworkers should run dedicated dust extraction and wear proper personal protective equipment during cutting, planing, and sanding. Additionally, because slight interlocked grain can cause planing tear-out, feed rates and cutter orientations should be monitored closely.
Is Brown sterculia subject to international trade restrictions under CITES?
No. Sterculia rhinopetala is not listed in the CITES Appendices (Washington Convention 2025). Heartwood natural durability is rated as Durability class 2 (durable) against fungi, Class D against dry-wood borers, and Class M (moderately durable) against termites, corresponding to use class 2 for interior applications under cover where dampness is possible.
Sources
Published October 31, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: CIRAD Tropix specifically notes that filling is recommended on Brown sterculia to achieve a good finish due to its coarse grain, which epoxy builders can address by skimming clear resin into the open pores prior to topcoating. (Source: CIRAD Tropix 7 technical sheet: Brown sterculia.)