Base coat cracking under the clear

[HiVoltage]

Well, first off, I'm very new to painting cars. But here is my scenario. I have a section on the back of my truck that had the paint damaged and in some sections removed by the previous owner. I think there was some sort of a protective sticker in between a the cab and the shell that when it was removed peeled paint with it.... anyway.... so the lack paint allowed surface rust to start. So, I sanded it all down with 400 and cleaned it all up. Roughed up the existing clear with 500 and prepped it all for paint. Spent a good chunk of the day masking everything off and today we sprayed.

First cleaned all surface with that degreaser stuff and a tack cloth. Then laid down a light coat of etching primer, waited 15 minutes and sprayed the second coat. Per the instructions on the primer container, we waited an hour before spraying the base coat. Now, we used 4th dimension by sherwin williams base coat. We did 2 coats of base with a 7 or 8 minutes flash time between coats. So far so good... everything looks perfect. Then we waited 30 minutes and sprayed the Acme Finish 1 clear coat. First coat laid on beautifully. Had a few thin spots, but nothing major. Waited another 7-8 minutes and sprayed the second coat. As soon as that second coat was on, the base coat began to crack and texture under the clear. Don't know why it did this. Should we have used a sealer in between the etching primer and the base coat? Not enough flash time?? Incompatibility between products?? Or just garbage products?? Anybody have any input for this noobie??

Thanks

 

[TAZ]

Welcome!

Without seeing first hand I could only guess.

My guess would be that one of the products were incompatible with the reducer, hardener or the clearcoat itself.
I could have been the etching primer that gave way, but made it appear that it the basecoat that had the problem.

Probably should have primed the areas first with a good 2-part primer, let it dry, resand and now you are ready to apply your base and clear.

Do a test panel to confirm which was the culprit.
Do just the base and clear. If nothing happens, this this would prove it was the etch primer. If the clear wrinkles the basecoat, then it was the basecoat and clearcoat incompatibility.
One other scenario is it could have been the original paint lifting or wrinkling, but I doubt this.

 

[HiVoltage]

Thanks Taz..... Think you could be right about the primer as the whole area wasnt primed.... But it was only the section that was primed that cracked. I'll try to get some pics and post them up before I sand it all back down. Do you have any recommendations on the primer? And when you say 2 stage primer, I'm guessing primer/ sealer??

 

[TAZ]

Sounds like it's the etching primer then.

As far as the 2 "part" (not stage), you can use any decent primer that is catalyzed like "5 star" 5454 and the 5457 hardener.

Just spray it, let it dry for about 4+ hours. sand it, then spray over it.

 

[HiVoltage]

Here are some pics of the cracks

 

[TAZ]

yea, I would say it's the etch primer giving away from what I see. I think if you tear away a little chunk and look at the bottom of the chunk, you'll see the culprit.
Try that, just take a little piece of the lifted area only. Turn if over, and see if you can tell if it was the etching primer.