In-Service Movement vs. Green-to-Dry Shrinkage
When selecting timber for an epoxy river table, woodworkers frequently examine total green-to-dry shrinkage values. While total shrinkage is critical during the initial drying phase from fresh timber down to seasoned lumber, it reveals very little about how a finished piece behaves inside a climate-controlled home. By the time epoxy is cast along the live edge, the wood is already seasoned. In an indoor living room or dining area, the tabletop does not cycle from green to dry; instead, it undergoes modest seasonal moisture shifts of just a few percentage points.
For this reason, the volumetric shrinkage coefficient—measured as the percentage of volume change per 1% change in wood moisture content—is the metric that matters most for long-term river table integrity. Derived from the technical sheets published by CIRAD Tropix 7, this value tracks how aggressively wood expands or contracts during seasonal humidity swings. High-movement species exert severe mechanical shear against rigid epoxy seams, which can lead to stress cracks, glue-line separation, or surface unevenness. Slabs with low shrinkage coefficients undergo minimal dimensional change per unit of moisture fluctuation, making them inherently more stable partners for cured resin.
The St/Sr Ratio: Predicting Slab Cupping and Distortion
Beyond overall volumetric movement, the direction of dimensional change determines whether a slab stays flat or distorts. The CIRAD Tropix 7 data includes the St/Sr ratio, which is the ratio of tangential shrinkage (St) to radial shrinkage (Sr). Because wood shrinks roughly twice as much along the growth rings (tangentially) as across them (radially), differential stress develops across the face of a board.
- High St/Sr ratios (above 2.0): Woods such as Cryptomeria (2.7), Rosewood Para (2.6), Itauba (2.6), Rubberwood (2.5), Jelutong (2.4), and European Oak (2.2) exhibit a pronounced imbalance between tangential and radial movement. Slabs from these species carry an elevated risk of cupping, warping, and twisting when atmospheric moisture levels rise or fall.
- Balanced St/Sr ratios (near 1.1 to 1.5): Woods such as Jequitiba (1.1), Senegal mahogany (1.1), Coconut wood (1.1), Makoré (1.3), Massaranduba (1.3), European Walnut (1.4), and African cordia (1.4) demonstrate much more uniform dimensional shifts, significantly reducing the mechanical drive toward cupping.
Ranking CIRAD Woods by Volumetric Shrinkage Coefficient
The dataset below ranks species from the lowest volumetric shrinkage coefficient (most stable in service) to the highest (least stable in service), paired with each species’ corresponding St/Sr ratio.
Most Dimensionally Stable (0.25 to 0.37% per % MC)
At the top of the stability rankings, African cordia leads with a volumetric shrinkage coefficient of 0.25 and a low St/Sr ratio of 1.4. It is followed by Rengas at 0.29 (St/Sr 1.8). A tight grouping sits at 0.33, including Ceylon Satinwood (St/Sr 1.5), Agba (St/Sr 2.3), and Cryptomeria (St/Sr 2.7). Guanacaste and Jelutong both measure 0.35, while Grenadillo and Scented Guarea sit at 0.36. Atlas Cedar, Idigbo, and European Walnut all share a 0.37 coefficient alongside balanced St/Sr ratios of 1.4 to 1.5, whereas Black wattle measures 0.37 with a higher St/Sr ratio of 2.3.
Moderate In-Service Movement (0.39 to 0.50% per % MC)
Many classic furniture woods occupy this intermediate range. Merbau measures 0.39 (St/Sr 1.6), Makoré registers 0.40 (St/Sr 1.3), and Peruvian Walnut matches at 0.40 (St/Sr 1.9). At 0.41, we find Aningeria, Cerejeira, Gedu nohor, Kauri, and Rubberwood. Kosipo and Utile both post 0.42. At 0.43, species include African walnut, Black Guarea, Iatandza, Mengkulang, as well as Jequitiba and Senegal mahogany, both of which feature an exceptionally low St/Sr ratio of 1.1.
Further along, African Padauk, Afzelia, and Iroko register 0.44 with St/Sr ratios of 1.5 to 1.6, while European Oak posts the same 0.44 coefficient but with a higher St/Sr ratio of 2.2. Woods with 0.45 include Haldu, Niangon, Piquia, Scots Pine, Tchitola, and Yemane. At 0.48 sit European Ash, European Larch, Izombe, Nyatoh, Pyinkado, and Red grandis, followed at 0.50 by Eyoum, Sycamore Maple, and Tauari.
High In-Service Movement (0.51 to 0.75% per % MC)
Species in this upper bracket expand and contract heavily with every percentage point of moisture change. Mid-tier hardwoods like Curupixa (0.51), Garapa (0.52), Berlinia (0.53), European Beech (0.54), and Bilinga (0.55) lead into dense exotic timbers. The highest coefficients in the dataset belong to Okan (0.61), Limbali (0.62), Moabi (0.64), Cupiuba (0.66), Angelim pedra (0.67), Angelim vermelho (0.68), Mora (0.68), Ekki (0.69), Red balau (0.69), and Wenge (0.69). At the very peak of in-service volumetric movement are Congotali (0.73), Cumaru (0.73), Snakewood (0.74), and Massaranduba (0.75).
| Wood | Volumetric shrinkage coefficient (% per % MC) | Ratio St/Sr |
|---|---|---|
| African cordia | 0.25 | 1.4 |
| Rengas | 0.29 | 1.8 |
| Agba | 0.33 | 2.3 |
| Cryptomeria | 0.33 | 2.7 |
| Ceylon Satinwood | 0.33 | 1.5 |
| Guanacaste | 0.35 | 2.0 |
| Jelutong | 0.35 | 2.4 |
| Grenadillo / Grenadille d’Afrique | 0.36 | 1.7 |
| Scented Guarea (Bossé Clair) | 0.36 | 1.7 |
| Black wattle | 0.37 | 2.3 |
| Atlas Cedar | 0.37 | 1.5 |
| Idigbo | 0.37 | 1.4 |
| European Walnut | 0.37 | 1.4 |
| Merbau | 0.39 | 1.6 |
| Makoré | 0.40 | 1.3 |
| Olon | 0.40 | 1.5 |
| Peruvian Walnut | 0.40 | 1.9 |
| Aningeria | 0.41 | 1.9 |
| Cerejeira | 0.41 | 1.9 |
| Gedu nohor | 0.41 | 1.7 |
| Kauri | 0.41 | 1.5 |
| Rubberwood | 0.41 | 2.5 |
| Kosipo | 0.42 | 1.4 |
| Utile | 0.42 | 1.4 |
| African walnut | 0.43 | 1.6 |
| Black Guarea (Bossé Foncé) | 0.43 | 1.6 |
| Iatandza | 0.43 | 1.8 |
| Jequitiba | 0.43 | 1.1 |
| Mengkulang | 0.43 | 1.9 |
| Senegal mahogany | 0.43 | 1.1 |
| African Padauk | 0.44 | 1.6 |
| Afzelia | 0.44 | 1.5 |
| Iroko | 0.44 | 1.5 |
| European Oak | 0.44 | 2.2 |
| Haldu | 0.45 | 2.0 |
| Niangon | 0.45 | 2.1 |
| Piquia | 0.45 | 1.4 |
| Scots Pine | 0.45 | 1.6 |
| Tchitola | 0.45 | 1.9 |
| Yemane | 0.45 | 2.1 |
| Cedrorana | 0.46 | 1.8 |
| European Ash | 0.48 | 1.7 |
| European Larch | 0.48 | 2.0 |
| Izombe | 0.48 | 1.8 |
| Nyatoh | 0.48 | 1.9 |
| Pyinkado | 0.48 | 2.0 |
| Red grandis | 0.48 | 1.7 |
| Eyoum | 0.50 | 1.8 |
| Sycamore Maple (Great Maple) | 0.50 | 1.7 |
| Tauari | 0.50 | 1.6 |
| Curupixa | 0.51 | 1.6 |
| Bintangor | 0.52 | 1.3 |
| Coconut wood | 0.52 | 1.1 |
| Garapa | 0.52 | 1.8 |
| Tasmanian oak | 0.52 | 2.0 |
| Berlinia | 0.53 | 2.1 |
| Etimoe | 0.53 | 1.7 |
| Tatajuba | 0.53 | 1.4 |
| Ayan | 0.54 | 1.6 |
| European Beech | 0.54 | 2.0 |
| Keruing | 0.54 | 1.9 |
| Louro vermelho | 0.54 | 2.0 |
| Mango (Machang) | 0.54 | 1.5 |
| Rosewood Para | 0.54 | 2.6 |
| Bilinga / Opepe | 0.55 | 1.7 |
| Dabema | 0.55 | 2.2 |
| Freijo | 0.55 | 1.5 |
| Pau mulato | 0.55 | 2.1 |
| Jacaranda | 0.56 | 1.5 |
| Mutenye | 0.56 | 1.8 |
| Niove | 0.56 | 1.3 |
| Suren | 0.56 | 1.7 |
| Zebrano | 0.56 | 1.3 |
| Mecrussé | 0.57 | 1.1 |
| Ovangkol | 0.57 | 2.1 |
| Cabreuva | 0.58 | 1.6 |
| Pau marfim | 0.58 | 1.8 |
| Muirapiranga / Bloodwood | 0.59 | 1.4 |
| Itauba | 0.60 | 2.6 |
| Okan | 0.61 | 1.4 |
| Tamarindo (Groçai-rosa) | 0.61 | 1.1 |
| Yellowheart | 0.61 | 1.1 |
| Limbali | 0.62 | 1.9 |
| Moabi | 0.64 | 1.3 |
| Preciosa | 0.64 | 1.3 |
| Cupiuba | 0.66 | 1.7 |
| Mukulungu | 0.66 | 1.1 |
| Angelim pedra | 0.67 | 1.7 |
| Angelim vermelho | 0.68 | 1.7 |
| Mora | 0.68 | 1.5 |
| Yellow balau | 0.68 | 2.3 |
| Ekki | 0.69 | 1.4 |
| Red balau | 0.69 | 1.8 |
| Wenge | 0.69 | 1.5 |
| Congotali | 0.73 | 1.4 |
| Cumaru / Tonka | 0.73 | 1.4 |
| Snakewood | 0.74 | 1.8 |
| Massaranduba | 0.75 | 1.3 |
Data compiled by BigEpoxy from individual CIRAD Tropix 7 technical sheets (average values for mature wood).
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: Even among species with severe volumetric movement, grain geometry matters: Mukulungu (0.66) and Tamarindo (0.61) exhibit high total shrinkage per percent of moisture change, yet their St/Sr ratio of 1.1 shows that tangential and radial dimensions shift almost equally, resulting in minimal cupping compared to species with severe directional differences. (Source: CIRAD Tropix 7 technical sheets (index).)