Comparing White Ash and White Oak for Tabletops
Choosing between White ash and White oak for an epoxy river table involves balancing mechanical strength against seasonal wood movement. Because cured epoxy does not expand or contract with ambient humidity changes the way timber does, physical properties such as shrinkage rates and dimensional change coefficients play a critical role in joint integrity. Figures cited below originate from the USDA Forest Products Laboratory Wood Handbook (FPL-GTR-282).
Weight and Density
At 12% moisture content, White ash has a specific gravity of 0.60, whereas White oak measures 0.68. This difference makes White oak slabs noticeably heavier when building large conference surfaces or thick dining tops. Higher density can give a finished table a substantial, grounded feel, but it also increases the dead load on table bases and mounting brackets.
Dent Resistance and Bearing Strength
For high-traffic dining tables and desks, resistance to everyday dings and compression under heavy hardware is essential:
- Side hardness: White oak provides a side hardness of 1,360 lbf at 12% moisture content, while White ash measures 1,320 lbf. Both species offer high resistance to surface denting from dropped silverware, writing implements, or everyday use.
- Compression perpendicular to grain: Under heavy base plates or steel legs, White ash shows a slight advantage with a fiber stress at proportional limit of 1,160 lbf/in², compared to 1,070 lbf/in² for White oak at 12% moisture content.
Stiffness and Strength for Spans and Overhangs
River tables often feature wide expanses where wood flitches flank a central epoxy canyon, requiring good resistance to sag and bending:
- Modulus of elasticity (MOE): White oak exhibits a modulus of elasticity of 1.78 million lbf/in² at 12% moisture content, closely matched by White ash at 1.74 million lbf/in². Both species provide outstanding stiffness across wide unsupported spans and seating overhangs.
- Modulus of rupture (MOR): In ultimate bending strength, White ash measures 15,400 lbf/in², while White oak tests at 15,200 lbf/in² at 12% moisture content. The structural capability of clear wood in both species exceeds ordinary tabletop demands.
- Shear parallel to grain: White oak reaches 2,000 lbf/in² in shear strength at 12% moisture content, while White ash tests at 1,910 lbf/in².
Seasonal Movement and Shrinkage
Differential movement between wood and cast resin creates shear stresses along the glue line. Slabs with lower overall shrinkage and a low ratio between tangential and radial movement remain more stable through seasonal humidity swings.
From green to ovendry conditions, White ash exhibits radial shrinkage of 4.9%, tangential shrinkage of 7.8%, and volumetric shrinkage of 13.3%. Its tangential-to-radial (T/R) shrinkage ratio is 1.6. By comparison, White oak shrinks 5.6% radially, 10.5% tangentially, and 16.3% volumetrically, yielding a T/R ratio of 1.9.
The dimensional change coefficients per 1% change in moisture content further illustrate this behavior: White ash has a radial coefficient of 0.00169 and a tangential coefficient of 0.00274. White oak moves more with each percentage point of moisture change, with a radial coefficient of 0.00194 and a tangential coefficient of 0.00376. White ash therefore places less mechanical stress on the resin interface during indoor humidity fluctuations.
Green Moisture and Decay Resistance
Freshly cut heartwood shows a green moisture content of 46% in White ash and 64% in White oak. For sapwood, White ash measures 44% green moisture content, while White oak reaches 78%. Slabs must be thoroughly dried to equilibrium before resin work begins.
Regarding durability, the USDA classifies White oak heartwood as Resistant to decay, while White ash heartwood is classified as Slightly or nonresistant. For indoor dining furniture, fungal decay is rarely a factor, but White oak provides natural resistance if a tabletop is placed in covered outdoor or high-moisture settings.
Figures from the USDA Wood Handbook (FPL-GTR-282), Tables 4-1, 4-3, 5-3b, 13-5 and 14-1. Clear, straight-grained specimens; real slabs vary.
| Property | White ash | White oak |
|---|---|---|
| Specific gravity (12% MC) | 0.60 | 0.68 |
| Side hardness, lbf (12% MC) | 1,320 | 1,360 |
| Modulus of rupture, lbf/in² (12% MC) | 15,400 | 15,200 |
| Modulus of elasticity, million lbf/in² (12% MC) | 1.74 | 1.78 |
| Compression perpendicular to grain, lbf/in² (12% MC) | 1,160 | 1,070 |
| Radial shrinkage, green to ovendry (%) | 4.9 | 5.6 |
| Tangential shrinkage, green to ovendry (%) | 7.8 | 10.5 |
| Volumetric shrinkage, green to ovendry (%) | 13.3 | 16.3 |
| Dimensional change coefficient, tangential (per 1% MC) | 0.00274 | 0.00376 |
| Dimensional change coefficient, radial (per 1% MC) | 0.00169 | 0.00194 |
| Green MC of heartwood (%) | 46 | 64 |
| Tangential/radial shrinkage ratio (calculated) | 1.6 | 1.9 |
| Heartwood decay resistance (Table 14-1) | Slightly or nonresistant | Resistant |
Which Species to Choose When
Neither species is universally superior; selection depends on your project goals:
- Choose White ash: When dimensional stability along the epoxy bond line is your highest priority, when lower overall table weight is desired, or when you want superior compression strength perpendicular to the grain under base attachments.
- Choose White oak: When your design benefits from a heavier, denser piece, when the project demands natural decay resistance, or when maximum shear strength parallel to the grain is favored.
Regardless of which species you select, ensure the lumber is properly dried to indoor equilibrium, seal raw edges thoroughly, and consult the resin manufacturer’s technical data sheet for pour depth and preparation guidelines.
Sources
Published October 28, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: When drying raw flitches before casting, keep in mind that White oak sapwood starts at 78% green moisture content (and 64% in the heartwood), compared to only 44% in White ash sapwood and 46% in its heartwood. That higher volume of initial water means thick White oak live-edge slabs require substantially longer conditioning times to reach indoor equilibrium before resin work can safely proceed. (Source: USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282, 2021).)