Possible causes are:
- Low temperature. The epoxy will need more time to cure if your room temperature is lower than the recommended range. Applying heat to the project will help it finish curing.
- Off-ratio mixing. There may have been too much or too little hardener, which directly affects the cure time of the batch.
- Insufficient mixing. You may not have mixed long enough for the resin and hardener to be adequately mixed for a proper cure. Always mix thoroughly for a minimum of 3 minutes.
- Incorrect resin or hardener. Using UVPoxy resin or hardener with Liquid Plastic resin or hardener will cause under curing, overreacting, or other adverse effects to the batch.