OldSchoolDood
Let's say you have a model already primed with Rustoleum auto primer and you used Rustoleum paint for a finish. After seeing some awesome auto paint colors you want to change it. You already know the auto paint is compatible with the primer, so would it be safe to prime over the Rusto paint job and apply the custom auto color? I've seen nightmare pics of incompatible paint jobs before but I was wondering if this could be done safely.
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IME, putting a lacquer over any enamel underneath is asking for trouble. Is the new paint lacquer or enamel or other?
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OldSchoolDood
I'm not 100% certain but the Rusto enamel paint shouldn't be a lacquer. The auto finishing paint is acrylic enamel. But since I'll be priming over the old enamel paint, it should be safe to use the acrylic enamel there after?
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You would think so. But in my experience, sometimes enamels crinkle up even a previous coat from the same can. And many primers are lacquer based (Such as the rusto auto filler primer) and are risky on top of previous enamel. This is a reason why I don't buy enamels any more.Originally Posted by Gary Byrum
There's only one way to find out for sure...
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Micro Craftman/ClusterNut
Actually Gary unless the Automotive finish your looking at Says it an Acrylic Enamel on the can it's more then likely some form of Poly-Urethane (nothing more then a Plastizied Enamel). But the Catalyst and Thinners are sometimes a little hotter (stronger) then those used in Rattle Can Enamels. They would be what cause the problem IF applied too heavily the first coat or two.
I'd read the New Paint Can very closely, If in fact it is an acrylic Enamel you should be able to simply rough-up the Rustoleum surface with a bit of 320 sandpaper and shoot the new color over the old. If you need to re-primer to cover a dark color or some dings and dent repairs there shouldn't be any adverse reaction at all using the Rustoleum Primer. Just keep the first couple passing coats light and let it have a good 1/2 hour between coats to outgas, then go for a 3rd wet finish coat to bring up the gloss.
If the new Auto paint is a rattle-can Polyurethane then I'd be very careful to use a matching primer over the old Rustoleum after roughing up the surface with 240 or 320grit.
As marc_G mentioned Enamel or Poly-Urethane over Lacquers is no problem. Lacquer over Enamels is almost surely going to Lift,Craze or Crinkle.
Last edited by Micromeister; 15th August 2012 at 07:15 PM.
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OldSchoolDood
This paint was mixed at the NAPA store and is not a rattle can and the guy that mixed it said it was acrylic enamel. The guy (very savvy with paint btw) said that I could use the auto primer over the old Rusto paint (which btw worked very nicely) and I would be safe using the auto paint especially since I am applying it with an air brush. I figured since I get so many mixed opinions here on TRF that it might be wise to just go and ask the paint chemist himself. That being said, thank you all that weighed in and I'll be sure to post a pic of the finished MR 1 in the gallery.
fin
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BAR jack of all trades
The only way to REALLY know is to do a paint test... using the same materials you plan to use, and making sure they're all applied the same way and cured properly. The other alternative is to "shoot it and hope".
The rule of thumb is that you can apply enamels over lacquers but NOT lacquers over enamels. The reason is that lacquers use "hotter" more active solvents that will easily dissolve the fairly soft enamel coats beneath. Enamels, on the other hand, use "weaker" solvents which are easily handled by the harder, more brittle lacquer coats over which they're applied.
Thing is, nowdays it's very hard to discern exactly WHAT the paint formulation exactly is... lacquers are fairly uncommon anymore and one really has to look for them to find them, basically, due to volatile organic compounds regulations (VOC regs) put out by the EPA which have mandated that the hotter solvents used in lacquers be limited toward phaseout, so lacquer is basically a "specialty paint" nowdays where it's harder but more brittle surface finish or very fast dry times are better suited to the job at hand. Usually nowdays lacquer is either industrial finish, some limited automotive finishing products, and a few other minor applications. The vast majority of spray paint now is enamel, usually alkyd enamel, but basically there are SO many different formulations for it that the way they behave from brand to brand and how compatible they are with other finishes is pretty much a crapshoot. The conditions under which they're sprayed, how they're sprayed, the formulation being applied and being applied over, how much is sprayed, how long the old coat has cured, etc. all play wildcard roles...
So basically any answer you get here is going to be a 'best guess'... it might have worked for them just fine, but it might have worked for any number of reasons previously mentioned that just happened to come together just right. You might do the same thing with the same materials, but any of the "wildcards" such as environmental conditions, how you spray the material, how thickly you spray it on, how long your undercoats have cured, etc... might lead to a bad failure... so it's sort of a crapshoot...
I've heard of people applying lacquers over enamels successfully, but it's DEFINITELY NOT a beginner technique, and the risk of failure is DEFINITELY HIGH.... It mainly involves spraying ultra-light coats of lacquer many times onto the undercoats to build up the outer coat, not putting down enough of the hotter lacquer solvents to soften and craze the underlying soft layers of enamel. One mistake just putting a LITTLE too much lacquer though, and bam! huge crazed mess...
Good luck on your project! OL JR
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If it crinkles up, I recommend letting it just dry that way and then christening the rocket with the name: "I wanted it that way"
"If at first you don't succeed, Scream and Leap!"
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OldSchoolDood
LOL, that's funny! I gave it a second coat of primer today and it went very well. Fortunately the humidity was about 30+. I figure, if I'm still smelling it, it's degassing. I'll give it a few days before I shoot the finals on it. Better safe than sorry.
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You have always been here
Good luck. Taking it slow is the right thing to do here!
"If at first you don't succeed, Scream and Leap!"
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