There can be several factors why this happens:
- Not enough catalyst has been used.
- The resin has been spread to thin. The minimum recommended depth is 5mm.
- The outside temperature is too cold. On cold days the resin will cure but will take longer.
- It is not recommended to use in conditions below 10°c
- *TIP* Expose the resin to U.V light (Sunlight or U.V lamp) to promote the curing process