Long time drying

[Jim]

Seeking advice: Anyone have advice on what to do when paint or clearcoat won't dry completely?
I've recently completed building a new model, but can't finish the job because the paint doesn't seem to want to dry completely. Not all of it, mind you. Just a few spots on the wings and fuselage. To explain:

My usual practice is to paint the model with acrylics, then after drying, give it a coat of clear enamel (Floquil Railroad Colors Crystal Clear-Cote) to provide a smooth, shiny surface that the decals can best adhere to. Sometimes, if it's particularly humid or cold in the workshop, this may take a day or more to dry completely. Then, after attaching the decals and letting them set, I like to give everything a final coat of Crystal-Cote to seal the decals and make everything look sharp visually.

But this time, for some strange reason, the primary layer of clear-coat won't seem to dry completely. It remains tacky in spots a good two weeks after application. I set it aside in a climate-stable space, but the tackiness persists. I'm concerned that applying decals and another coat of crystal will result in disaster. I've thought about hitting it with a heat gun or hair dryer, but the idea of what might happen gives me the fantods!

Anybody have any ideas or suggestions what to do?

[Model Maker]

Hi Jim

I did a little research and I would suspect there is either an issue with the "drying chemicals" not being evenly distributed when you applied the base coat. Or there was a humidity / temperature issue. If it's a moisture issue, I would suggest trying the hair dryer on low and keeping it a good distance away from the affected areas. Rather than a prolonged exposure to the hair dryer, it may be better to apply heat in frequent short duration applications (1 or 2 minutes). You should be able to test the temperature by testing on a scrap of wood and then touching the surface to see how hot it becomes. I would try for a "warm to the touch" duration. by adjusting the distance from the model and also the angle of air flow impingement, you should be able to obtain an acceptable temperature. In my opinion a heat gun would create too much risk.

Good luck and let us know the outcome of your efforts. - ken

If the issue is a chemical issue rather than an evaporation issue you may wish to go over the affected areas with a reapplied light coat to re-introduce the curing chemicals ensuring the temperature and humidity conditions are correct. This would be a little risky in the event the second light coat hardens and seals in the softer first coat.

[lastvautour]

I have had some success with adding a mist coat. I don't know if the underlying coat dried or if the top coat just covered the tacky area. Let us know how things work out for you.

Lou

[Ken Pugh]

In future, you may consider using an acrylic clear coat.  I have great success with them.  If you are concerned with smoothness of the coat, just do a couple of coats with light sanding after each dries and cures.  Read the instructions to make sure you are doing it right by the manufacturer.  Acrylic does cure and not just dry.  The instructions will cover what you need to know.

The best clear finish I have used is Minwax Polycrylic.  I get no yellowing over time with any acrylic clear I have used and they are very durable, protecting the model from handling damage.

[Jim]

Well, thanks you for your help, gentlemen. I tried giving it the gentle hair dryer treatment, and that seems to have done the trick. I'm always anxious about using heat for fear of loosening up the glue and causing even worse trouble. But now I can attack the decals without fear, and will soon be sharing the results with you.
Thanks again, friends. 

[lastvautour]

I may have asked before, however, what do you use for rigging?

Lou

[Jim]

I usually use monofilament fishing line — the real light 2-4 lb. test stuff used for fly fishing leader tippets. Just paint them silver or aluminum after installation.

[lastvautour]

Thank you Jim.

Lou

[Jim]

Oh, I almost forgot: I usually use light gauge wire for the "X"- or cross-bracing wires between the fore-and-aft interplane struts and drag wires, as well as the center-section and undercarriage struts (when I do rig them). I use bits of old banjo strings for the wires. Any light-gauge music wire will do.

[lastvautour]

Thank you Jim.

Lou