Measure each crack at its widest and deepest point (poke a thin wire in for depth). Cracks taper to nothing at the bottom, so they hold about half of a box of the same size; round knot holes hold π/4 of their square.
Example: a crack 36" long, ¼" wide and 2" deep is 36 × 0.25 × 2 × 0.5 = 9 in³ ≈ 5 fl oz, about 6 fl oz with soak-in, poured in four ½" layers.
| Void depth | Use |
|---|---|
| Hairline to ¼" | Thin penetrating or tabletop epoxy |
| ¼"–1" | Casting / medium-pour epoxy |
| Over 1" | Deep-pour epoxy, in layers (see the layer planner) |
Tape the back of through-holes with packing tape first, dry the wood to about 8–12% moisture, and tint the fill black or with mica for a contrast look.
Multiply length × top width × depth × 0.5 (cracks taper), divide by 1.805 for fl oz, and add about 20% for soak-in. A 10 in crack ¼ in wide and ¼ in deep needs only about 0.2 fl oz, so your minimum mixable batch usually decides how much you mix.
Below about 2 fl oz of mixed epoxy, tiny measuring errors throw off the ratio and some resins cure poorly. Mix the minimum and use leftovers in a silicone mold.
A crack is an enclosed space that holds heat, so stay at or under your label's max depth; ½ in per pour is a safe default for most casting epoxies.
Small knot holes under about 1 in deep fill fine with casting epoxy. Use deep pour only for big voids and pour in layers.
More tools: resin calculator · mix ratio by weight · cure time · mold volume · tabletop coating · pouring too thick
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