acrylic urethane over lacquer?

[doug]

I'm planning to repaint the firewall on my '63 Impala with black acrylic urethane. The original white paint is lacquer. I planned to clean, scuff, and shoot. Will there be compatibility issues if I put urethane over the lacquer? Thanks for any guidance you can give...
Doug

[doug]

Anyone? If acrylic urethane is no good over lacquer, what paint would you recommend? I'm trying to avoid stripping the existing paint. This doesn't have to be show car quality, but I'd like to use something with a hardener for durability. The same paint will end up on the frame, tie rods, control arms, inner fenders, etc.

If I could still search the old forum's posts, I'll bet I could find the answer to this question- but I haven't seen a way to do that. I know there are some knowledgable folks around here, I've learned a bunch already just lurking around. Thanks in advance for any guidance you can give.
-doug

[Phil V]

Doug, generally its not a good idea to spray urethane paint over a lacquer paint. If I were in your situation I would consider spraying a couple medium coats of epoxy primer over the lacquer paint. Let that sit for a while (longer than a half hour but still within the time recoat window). If you are going to have a lifting problem with the lacquer then it will lift from the epoxy primer.
If it doesn't lift then you're good to go to apply your urethane topcoat over the epoxy primer. Past experience tells me you should be fine with no short term or long term problems, in this particular situation.

[doug]

Thanks Phil. I started reading the product sheets for PPG UE topcoats and none of them seem to like lacquer bases. I guess I will shoot some epoxy first. So far the only PPG epoxy primer I've found that mentions compatibility with OE lacquer is the Delta DPLF, and even that has a disclaimer: "Caution: When DPLF is sprayed over lacquer substrates or basecoat that is not crosslinked, and then allowed to set overnight before applying another coat of primer or a topcoat, lifting can occur. This can be avoided by applying the DPLF Epoxy Primer, color and clear coat in the same day or by adding 5% of DX57 RTS DBC."

-doug

[Len]

Doug
In "most" cases a factory applied lacquer will not react poorly to an application of urethane but sometimes re coat lacquer can melt under a urethane coating causing the urethane to peel off later. If I were doing this job I'd probably apply a coat of hardened acrylic enamel in areas where the lacquer was going to remain.

When urethane was only on the market a couple years we painted a previously lacquered Porsche with Imron causing the lacquer to liquefy. The urethane slid off the car like cellophane off butter. What a mess.

[doug]

Thanks Len. That's good info. I'll post some pictures when I get around to shooting this. I've got a lot of grease to clean off!