How can I determine is the old primer is lacquer?

[PsychoThruster]

I'm working on a 73 mach 1 mustang and have just finished(or so I thought) sanding down the old paint. The body is solid, there are a few spots of filler here and there, but nothing major and no rust issues. The car had one repaint in the 80's or 90's before I had it, and I have sanded off the repaint, through the original base coat, and in some spots down to the bare metal. I smoothed the car with 150, 220, then 340 grit sand paper. So my situation right now is that the car is sitting with some old paint and primer here and there, and bare metal in a few other spots that has all been smoothed and ready to accept primer. Now my problem is that I was planning to order the primer but was informed that the old primer might be lacquer which could cause massive problems once my urethane paint goes on. So is there a way to determine if this primer from nearly 40 years ago is lacquer or not? I would like to avoid stripping it to bare metal if I can.

[easymoney]

i would bet that it is lacquer if it is that old. to find out if it is lacquer rub the primer with a rag soaked with lacquer thinner and if it dissolves with the thinner it is lacquer.

[PsychoThruster]

i would bet that it is lacquer if it is that old. to find out if it is lacquer rub the primer with a rag soaked with lacquer thinner and if it dissolves with the thinner it is lacquer.

Okay, awesome. Thanks. This will also make stripping it to bare metal easier as well if it is indeed lacquer based primer.

[another2centsworth]

If it was repainted it possibly could be un-catalyzed enamal if it comes off with laquer thinner and a rag. Either way strip it.

[PsychoThruster]

Well took some lacquer thinner to it earlier today and it didn't seem to come off at all. I soaked the rag in it then proceeded to scrub as hard as I could at a few different spots and managed to succeed in getting a bit of it to smudge, but that's it. The spots I just let soak up the thinner for a few minutes showed no signs of dissolving whatsoever. In the end it seems the only time the rag picked up any residue was when I scrubbed the hell out of it. I tried this on five different spots all over the car and it was the same each time. I feel like if it was lacquer based it would come off cleaner not just smudge, and not require me to put all of my strength behind the rag when rubbing. Thoughts?

[Len]

Well took some lacquer thinner to it earlier today and it didn't seem to come off at all. I soaked the rag in it then proceeded to scrub as hard as I could at a few different spots and managed to succeed in getting a bit of it to smudge, but that's it. The spots I just let soak up the thinner for a few minutes showed no signs of dissolving whatsoever. In the end it seems the only time the rag picked up any residue was when I scrubbed the hell out of it. I tried this on five different spots all over the car and it was the same each time. I feel like if it was lacquer based it would come off cleaner not just smudge, and not require me to put all of my strength behind the rag when rubbing. Thoughts?

If it's original factory primer on a Ford then I doubt that it's lacquer. Anyway, if you're down that far, I'd recommend removing the existing coating just to be sure that you have a good substrate to lay your paint on. If you have a decent variable speed rotary sander/polisher like the one linked below you should be able to remove the remainder of the finish in a day or two then reprime with a good epoxy primer before spraying a filler primer.

Link

[James M]

I agree with the other guys. Strip all the outer surfaces of the car down to bare metal then apply a couple coats of epoxy primer. Any material (paint/primer) that you apply over old existing paint/primer is a gamble of an unknown factor that could cause the new paint/primer to crack, peel, bubble, flake off etc etc. Its not much more work to strip all the outer surfaces down to bare metal then you will have a sound foundation for you new paintjob.