Auto body repair & detailing: CRACKING ON NEWLY PAINTED CAR, cracked paint, corrosion protection

Question
I have a problem! I recently got my car painted and two weeks later the hood started cracking(like cracks in dryed mud) all over the top. It had some of this cracking before I had it painted and my repair man had sanded it down to the metal and it is worse now than before. He is going to re-paint but we are not sure that it will not do it again. Before noticing the problem, I have the car in very hot conditions for about 8 hours. Would this have something to do with it??  I would appreicate any help! Thank you very much!

Answer
Hi Barbara,

It sounds like a classic example of a lacquer primer. "Lacquer" is older technology finish. It sands great and drys very fast but it never cures hard which always leaves the finish prone to sand scratches, dieback, and cracking. Usually this happens when the product is applied too thick which is easy to do because it drys so fast and fills up imperfections so well. It's typically not used much anymore by technicians because of the disadvantages. However there are some die hard, old school body men out there that still demand to use lacquers because that's what they're familiar with. So if the fellow who done the work brags about being in business for 30 years that's most likely the problem. If it's someone who has only been in the business for 10 years or less or who has a very reputable paint shop then most likely they will have used newer technology product which typically don't cause those types of problems unless they reach temps of 200 degrees. The next question I would ask is, Are you certain that the finish was sanded down to bare metal? The reason I ask is because I have been around automotive technicians for a long time and the typical procedure for cracked paint is to sand through the cracks to the primer and refinish from there. If the finish would have been sanded all the way to bare metal then they would have had to use an epoxy primer or some other type of primer suitable for bare metal and corrosion protection. Which they typically charge more for this procedure. My bet is he sanded through the paint finish and realized the cracking was gone or almost gone so he used a filler primer and painted it and when it hit the hot temperature as you say, the original primer underneath (Lacquer Primer which never cures hard) caused the primer and paint on top to crack again. This time it's worse because the finish on top is fresh.

Make certain that the new repair goes all the way to bare metal and then an epoxy primer should be applied or some other suitable bare metal, corrosion resistant primer. Then a sandable URETHANE (not lacquer) primer be applied and then painted. This should stop the cracking.