There are a few different possible reasons.
The UV Light you are using is not correct
In order to cure Loon UV resins, your flashlight needs to emit UV light between 395 – 415nm. All of Loon's UV lights work in this range. If you choose to use a UV light from another manufacturer, please check with them to make sure they emit UV light between 395-415nm.
Your batteries are not fully charged
As your batteries start to lose a charge, so will the quality of your cure. You’ll notice the resin will remain tackier, take longer to cure, or won’t bind quite right to the materials underneath. If this happens, either recharge or replace your batteries.
Your resin cures, but is still tacky
Sometimes the resin can fully cure but leave a little bit of tack on the surface. You’ll know this is the case if the resin feels hard but a little sticky. This is common and can be blamed on the way oxygen affects the chemical reaction of the resin curing. If this is the case then there are a couple of options:
- You can use a little alcohol and wipe down the cured resin. This will knock off that tacky layer and you’ll be left with the completely cured resin underneath.
- You can use a stronger UV light, or replace your batteries with fresh ones.
It's not curing on waxed thread
If the UV resin cannot bind to the materials underneath then it will crack and lift off the fly. Waxed thread is the most common culprit here, but other smooth materials will cause the same problem.