Short answer: the most common reasons are: it isn't fully cured yet (many epoxies take about 7 days to reach full hardness; check your label), the room was too cold (cure slows a lot below the label temperature), the A:B ratio was off, or the piece is simply thin (thin bookmarks and keychains flex even when cured). If it's bendy after 24 hours, wait and keep it warm. If it's still soft after the full cure time on the label, the ratio or mixing is the likely cause.
| Scale | 0.01 g digital scale → | Measure the ratio exactly |
| Cups | Graduated mixing cups & stir sticks → | Graduated mixing cups |
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| What you see | Likely cause | What to do |
|---|---|---|
| Bendy at 24–48 h, hardening each day | Still curing | Wait for the label's full cure time at room temp |
| Bendy and the room was cold | Slow cure | Move it somewhere within the label's temperature range (cold-room curing) |
| Still soft or rubbery after full cure | Ratio or mixing off | Measure by the label (weight converter), mix fully, scrape sides |
| Thin piece flexes but isn't sticky | Thickness | Pour thicker or add a second layer |
| Bendy and sticky | Under-cure | See sticky resin fixes |
Use your resin's label times and your room temperature in the cure time calculator. Some resins are formulated with a little flex; the data sheet says if so.
Usually because it hasn't reached full cure yet; many epoxies list about 7 days for full hardness. Keep it in a warm room and check again.
If it's past the label's full cure time, the most likely causes are a cold room or an inaccurate ratio. A thin piece can also flex when fully cured.
If it's just slow curing, warmth and time fix it. If the ratio was wrong, it may never fully harden; recoat or recast with a measured batch.
More tools: resin calculator · mix ratio by weight · cure time · mold volume · tabletop coating · pouring too thick
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