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Testors spray enamel problem


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#1 Harry P.

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Posted 17 November 2012 - 02:57 PM

Ok... so I'm working on my latest model, a Pocher Alfa Monza. The body comes in several separate sections, so I decided to start with the rear end (the "cone" from the cockpit back).

The body parts are molded in red, and I want the model to be red, so all I did is sand all the imperfections out and spray red directly onto the plastic, no primer. Testors "Dark Red" enamel, 3 0z. can.

It looked great. Smooth, shiny, perfect. Just beautiful. But there was one problem... a run on the left side. I guess I could have lived with it, but instead I decided to fix it. I waited 2 days, then I wet-sanded the run until I had a nice smooth surface, and resprayed using more of the exact same paint. After a few minutes, the paint was all crackled and wrinkly, but not everywhere, only in sections. I thought that maybe it would all smooth out as it dried, but no luck. The paint looked like crap!

So I stripped it, and resprayed, just one coat. Again, smooth, shiny, perfect. And no runs this time, so no second coat.

Why did the paint self-destruct after I applied that second coat the first time around?

#2 Kris Morgan

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Posted 17 November 2012 - 03:08 PM

Some paints have a "window" for recoating. You must spray in a certain amount of time or wait quite a bit of time to shoot a second coat. Just an example,,Recoat within 3 hours or after 72 hours. I have no idea if this applies to Testors enamel, just tossing an idea out there.

#3 Ace-Garageguy

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Posted 17 November 2012 - 03:08 PM

There's a 'sensitivity window' for a lot of enamel-based paints. Sometimes, recoating can be done sucessfully within ah hour, and then not for 72 hours or more at 70deg. F. Some paint's labels give the recoat-time data, and some don't. Enamel dries on the surface first, like most paints, but the skin it forms on top is the cause of the problem. It retards evaporation of the solvents and really slows drying, and it's the skin that wrinkles when the solvents from subsequent coats hit it before it's through-cured.

This was a big problem with re-repairs back in the days when 1:1 cars were painted with enamel in bodyshops. Imagine having what happened to you, but on a full sized panel. Not fun.