lacquer paint misc question(s)

[Nine]

I have a car I painted several years ago using acrylic lacquer...its a solid color, that I clear coated with PPGs acrylic lacquer clear. Its held up pretty nice over the years but the lacquer clear isnt as protective as I would like....so I decided to wet sand the car and cover it with a urethane clear (DAU75). Before I do that, I need fix some dings and a dent. These are going to require the repaint of some panels...Im again going to use acrylic lacquer (which has been on the shelf for 5-6 years)...once the damage is corrected, I plan to wet sand the car with 800 grit. Then lay down 3 coats of clear, wet sanding with 1200-1500 and polish to a nice shine.
Does this plan sound feasable? I have concerns with the compatability of the urethane over the lacquer. I picked DAU75 because it says it can be used over lacquer. I also have a concern about the panel match....Im sure there are going to be spots where I sand through the old clear and others where I dont and the new painted surfaces will not have clear on at all.
This is the first time Im using urethene, so Im a little worried...Ive always used lacquer....the good old days of lacqurer, shooting with no mask, laying down six coats, polishing off three...Im sure my lungs look like a skiddles add...and this is also my first use of a HVLP gun.
thanks

[Phil V]

Nine, there are several things that could go wrong with spotting in fresh lacquer then clearcoating the whole car with a urethane clear. It will be like playing Russian Roulette as far as having problems of lifting and possible delamination later.

I've been spraying paint professionally for 36 years and I have never sprayed paint without proper lung protection. If you sprayed urethane paints without good lung protection it could kill you ---------------.

[Nine]

Hi Phil, thanks for the reply....I, of course, was going to use proper breathing systems when painting with the urethene, I was just remenising the old days when I didnt use masks....

When you said fresh lacquer, I might be misunderstanding,...DAU75 says it can be used over lacquer after 24 hours....I was planning on giving it more time than that (maybe a week). What do you feel (If any) would be a satisfactory time frame to wait before putting a urethene clear over lacquer? Do you feel the spotted areas offer more of a problem than the rest of the car?
Thanks

[Phil V]

The problem with combining lacquer base with urethane clear is that lacquer is referred to as a trapped solvent paint while urethane is a chemically catalysed paint. The lacquer air dries slowly and technically never dries while catalysed paint is chemically hardened in a short amount of time. With the lacquer basecoat off gassing for an extended period of time (length depending on film build and how much lacquer thinner was used in the lacquer paint) while the urethane clear is already hard/cured. The off gassing lacquer thinner works it way to the top of the lacquer paint but gets trapped there underneath the already hard/cured urethane paint. That causes delamination problems where the clear could come off in sheets.

Now specifically to your car --- If you spot in the color in repair areas with lacquer, keep the paint build thin and allow it to set for a minimum of 24 hours then you will probably be OK if you clear that with urethane. I still occaisionally spray urethane clear over lacquer custom paint like flames on bike tanks etc but at this point I know what I can get away with and where the line is that that will cause problems later, and know enough not to cross that line. There are a lot of variables involved so no simple set of rules apply to all jobs. My suggestion is go buy some PPG DBU with its reactive reducer in the color you need. Spray out a test panel or two to make sure the color is in the ball park as far as color matching. If its a decent match then spot in your repair areas with the DBU and clear the whole car with urethane clear.
Even then the existing lacquer paint on the rest of the car will absorb some of the urethane reducer that was added to the thin the urethane clear. So even that is not a given that everything will come out with no long term problems. The right thing to do is strip the car to bare metal and start over, then you are for the most part guaranteed no short term or long term paint compatibility problems.