Clear coat problem.

[Old Fart]

I think I know the answer but maybe someone can confirm my suspicions.

I painted a car body with Testors enamel paint, and let it dry for a few days before clear coating.  Everything looked great until about 2 weeks later when I noticed the finish had crazed badly.  Looked like mud when it dries out and cracks. 

I clear coated the paint with  pledge,  so I'm thinking there was a reaction between the enamel and the acrylic clear.  I removed the clear coat thinking it might have been the problem but the cracks are definitely in the enamel.

Anyone ever have the same problem? 

[GMCMAN52]

I had the same problem with my Tempest, I think that the enamel did not have enough time to dry. I've read where some guys let the paint cure for 7 to 10 days.

[High octane]

I think I know the answer but maybe someone can confirm my suspicions.

I painted a car body with Testors enamel paint, and let it dry for a few days before clear coating.  Everything looked great until about 2 weeks later when I noticed the finish had crazed badly.  Looked like mud when it dries out and cracks. 

I clear coated the paint with  pledge,  so I'm thinking there was a reaction between the enamel and the acrylic clear.  I removed the clear coat thinking it might have been the problem but the cracks are definitely in the enamel.

Anyone ever have the same problem? 

Did you use a lacquer clear over the enamel paint, or enamel clear? You can use enamels over lacquers, but not lacquers over enamel.

[Old Fart]

Did you use a lacquer clear over the enamel paint, or enamel clear? You can use enamels over lacquers, but not lacquers over enamel.

It was an acrylic clear coat.  Used Pledge.  Never had a problem using it over acrylics. 

[StevenGuthmiller]

The problem was that the enamel was not fully cured before the clear was applied.

This is one reason why I no longer use Testors enamels.

They take weeks to cure fully.

The acrylic cured much more rapidly than the enamel, hence the cracks.

An acrylic should be no problem over enamel paint, but the paint beneath needs to be completely dry before applying anything over it.

I used to box up my bodies that had been painted with enamel for up to 3 months before doing any polishing or the like.

Better safe than sorry.

Now I use nothing but lacquer for bodies.

Completely cured in a couple of days, at the most.

 

Steve

[High octane]

I spray my clear lacquer 24 hours after I have painted the body with lacquer colors, and never have a problem.

[935k3]

This a problem with Future over enamels. I love Future so I never use enamels on bodies for this reason. Nick(High Octane) please read the original post, he never said anything about using a lacquer clear coat so your reply is nt that helpful. I am glad you do not have any problems with what you use.

Edited May 24, 2017 by 935k3

[peteski]

The Pledge stuff (formerly known as Future)  Is a water-based acrylic coating which should be pretty much safe to use over any type of lacquer or enamel.  I agree with others that the problem was probably caused by the color coat still out-gassing under the layer of Pledge.

Drying painted parts in a food dehydrator for few days should fully cure enamel paints.

Edited May 24, 2017 by peteski

[Old Fart]

Thanks for the tips guys.  I was thinking that it might have been a reaction, but obviously I didn't allow enough time for the enamel to cure.

[Art Anderson]

The Pledge stuff (formerly known as Future)  Is a water-based acrylic coating which should be pretty much safe to use over any type of lacquer or enamel.  I agree with others that the problem was probably caused by the color coat still out-gassing under the layer of Pledge.

Drying painted parts in a food dehydrator for few days should fully cure enamel paints.

"Out-gassing" of enamel more than likely is not the problem here:   Enamel paints dry "click hard" in essentially two phases:  First, the solvent (the thinning) evaporates, and then the enamel resins harden by exposure to air.  This latter step takes longer than the "flashing off" of the thinner or solvent, which is why enamel paint takes a lot longer to cure out than say, lacquer.

Art

 

[StevenGuthmiller]

"Out-gassing" of enamel more than likely is not the problem here:   Enamel paints dry "click hard" in essentially two phases:  First, the solvent (the thinning) evaporates, and then the enamel resins harden by exposure to air.  This latter step takes longer than the "flashing off" of the thinner or solvent, which is why enamel paint takes a lot longer to cure out than say, lacquer.

Art

 

True, but the paint cannot harden if covered with something that hardens first.

I think of it a little like molten lava.

The hard shell that forms over the surface is no match for the softer stuff underneath & at some point, somethings gotta give.

Regardless of what the ultimate cause of the cracking was, it's always a bad idea to spray something that is incompatible over a paint that is not fully cured.

 

Steve

[peteski]

From my experience heat accelerates both, drying and hardening (oxidizing) of the enamels.  That is why I use the dehydrator to speed things up.

[Art Anderson]

True, but the paint cannot harden if covered with something that hardens first.

I think of it a little like molten lava.

The hard shell that forms over the surface is no match for the softer stuff underneath & at some point, somethings gotta give.

Regardless of what the ultimate cause of the cracking was, it's always a bad idea to spray something that is incompatible over a paint that is not fully cured.

 

Steve

Steve,  I can only recall just one paint job that cracked over time, and that is a Monogram '37 Ford Tudor Sedan street rod that I built in 1987, painted it with automotive lacquer too.  I've done dozens of model cars over the years with automotive lacquer, and that was the only one to have paint that cracked.

That said, I almost never use a clear coat on any model car project, but when I do, it's always been in the same brand and type of paint as the preceding primers and color coat.

Art

[StevenGuthmiller]

Steve,  I can only recall just one paint job that cracked over time, and that is a Monogram '37 Ford Tudor Sedan street rod that I built in 1987, painted it with automotive lacquer too.  I've done dozens of model cars over the years with automotive lacquer, and that was the only one to have paint that cracked.

That said, I almost never use a clear coat on any model car project, but when I do, it's always been in the same brand and type of paint as the preceding primers and color coat.

Art

I've had it happen a couple of times with automotive lacquer too, but that was when I was using Testors clear lacquer over it.

Since I've started using automotive lacquer for everything, I have had no issues.

That being said, with the OP using enamel for his color, I personally would not put anything over it, except possibly enamel clear, for the period that it takes for the base color to thoroughly dry.

With the slow pace at which enamel dries, especially Testors enamels, I think you would be opening yourself up to this sort of problem if you did.

 

Steve