Hey guys, I was having this issue too, and the tacky finish on my flies was collecting dust & dirt and making my UV wingcases and heads appear dusty and not clear.. I emailed Loon and this is the response I got.
Murray those flies you tied me way back did have a really nice UV epoxy shell on them. I may have to try the UV clear cure as well!
Hey Steve,
There is a short answer to your question and a long answer. I'll start with the short answer in case you're not interested in the long one!
The short answer: all UV resins are subject to remaining a little tacky due to the way that the resins interact with oxygen in the air. It's not an issue of light, amount of time exposed, or anything that you're doing... it's that darn oxygen. The quick fix is to cure your resins and then wipe them down with an alcohol swab. This will remove the uncured resin from the top of the applied resin and you'll have a tack-free fly.
The long answer....
The science:
The tack that you're experiencing is the result of "oxygen inhibition", which is a fancy way of saying that oxygen inhibits the outermost layer of applications of UV-curing resins to fully set up. In other words, the application should be cured all the way through, save that outermost layer that still feels tacky. If you picture a cross section of the resin, then imagine it curing from the inside out. The outermost layer, which is exposed to the ambient air, may remain tacky even though the rest of the applied resin is fully cured.
The variables:
Overcoming the effects of oxygen inhibition and producing a tack-free surface cure is dependent upon several factors, including:
Heat generated by the UV curing system
Intensity generated over the entire UV spectrum (200-420 nm)
Exposure time
The benefit:
The tacky exterior provides a more suitable surface for bonding between subsequent layers.
I hope that help Steve. Thanks for the email!
Brett