I am having issues with paint cracking on the roof of my 79 between the T-tops and rear window. It is in the process of being repainted. It was completely stripped down. But, during the repainting process, the second coat is cracking. The cracks typically don't appear until the paint has been on 24-36 hours. Looking for likely causes and fixed. Thanks in advance for your input. We are using an epoxy primer and paint from the same manufacturer.

 

Not knowing where you live....or what temperatures you are painting at....and how much epoxy you are applying on the panel BEFORE you apply the paint....and HOW LONG you are allowing THAT epoxy to dry BEFORE you apply paint......my guess.....is that you are trapping the solvents in the epoxy and it is outgassing and causing these cracks in the paint that DRIED so fast...because it sealed up the epoxy that was still not quite ready for paint to be shot directly on top of it.

Regardless IF the information of the epoxy you are using states that you can shoot paint on it in 30 minutes....DOES NOT mean that you should DUE TO your current temperatures and HOW MUCH you are actually applying on the panel when you apply the epoxy.

IF there is a required amount of mil thickness of this epoxy to be applied....and you are just 'guessing' on how much you are applying. That is where you might have an issue IF you follow the flash times that they say you can shoot paint on top of it.and you are on the low side of ambient air temp.

Keep in mind about ALL paint products use ambient air temperatures as a gauge. So ambient air temp is from 70F to 85F....at 50% hu8midity.

Also NOT knowing if you are double coating the epoxy or applying two coats with flash time in between the coats and the air temps are colder than normal ambient air temps..

When you get lower than normal ambient air temps...your flash time can increase greatly to compensate for the colder temp and higher humidify. So 30 minutes can turn into an hour or two. So it depends. How much you are putting on and the temperature/humidity.

The basecoat can also cause this due to the first coat went on way to thick. And not knowing what grade of reducer you are using...I cannot offer any more on this. ...other than it needs to all come back off and done again....or at least I would if it were in my shop and this occurred. Or at least get into it and see if anything is still 'wet' or gooey

And IF you have any fears....shoot something else to make sure you are getting it to work so you do not have to do this all over again.

DUB

***EDIT***

Not that it matters to some and I know you did not ask. But I mask off the clips for the rear window trim to keep paint build up off of them so I do not run into uses when I go to reinstall the trim.