Is it normal for resin to shrink while curing?
Why Shrinkage Happens
Shrinkage occurs because the resin molecules cross-link and pack more tightly as they cure. Epoxy usually shrinks less (around 1-3%) than UV resin, which can shrink 5-10% depending on the formulation. This is a natural part of the curing process.
Shrinkage can cause problems like dimpling, warping, or pulling away from mold edges. It's more noticeable in thick pours or when the resin is not mixed correctly.
- Epoxy: typical shrinkage 1-3%.
- UV resin: typical shrinkage 5-10%.
- Shrinkage is higher in thick, fast-curing pours.
How to Manage Shrinkage
You can reduce shrinkage issues by mixing resin and hardener thoroughly but gently to avoid introducing air. Pour in thin layers for UV resin, and for epoxy, use a slow-curing formula if possible. Also, allow the resin to cure at room temperature; heat can accelerate curing and increase shrinkage.
If you're casting in a mold, a mold release can help the resin pull away cleanly without tearing. For critical dimensions, consider making a test piece to see how much your specific resin shrinks.
- Mix according to the manufacturer's ratio.
- Avoid whipping in air; stir slowly.
- Cure at consistent room temperature.
- Use mold release to prevent sticking.
Common mistakes
- Thinking shrinkage means the resin is defective; it's a normal property.
- Overheating the resin to speed curing, which can increase shrinkage and cause cracks.
- Not accounting for shrinkage when casting parts that need to fit precisely.
