Paint guys. Paint shrinking and cracking

[axisg]

Back story: Ended up in a fender bender couple months back with the 99' work truck. Got wedged between a cube van and a UPS truck on the highway. Thankfully even with 5 rigs involved nobody was hurt. I was able to drive away from scene but both fenders and mirrors needed to be replaced. Thank goodness for the parts truck to donate bumper, mirrors and headlights. I was able to re-use the existing hood.

So went with new fenders. Bought paint and used the Omni line stuff as I have in the past. Single stage ( same colour as Monte ), used their primer and hardener. With the new fenders ( darn they are thin compared to what I pulled off ) I gave them a good 200 then 400 sanding before primer then paint. I am no rktpwrd5 or Hafrod. Spray it and toss in some dirt for character and "it will work its way out" kinda finish is more my style. However the fenders surprisingly turned out fairly decent for a work truck. Pulled the hood for a couple days ( I wasn't worried about the dents ). 200, 280, 400, scuff the rest with scotchbrite so I dont burn off the edges. Primered it 3x coats. Went to work for the day and let it sit overnight on Thurs. ( hot and humid if that matters ), Scuffed it with 400 then 2x topcoats Friday morn and went to work.
Darn thing looked good enough for who it was for considering I was painting it outside in the back yard. I had 1 run that I was able to sand out Sat morn then I put on 2 more top coats.
It was over 100deg ( merican ) and humid most of that week. My air drier ( x2 ) did its thing and I had no water coming out the gun.

So now weeks later I am having issues with only the hood. The paint is shrinking and I am seeing cracking in some of the finish. Did I go too heavy with the coats ? Fenders are fine.

oh .. and I hate the chrome front bumper....

 

[spongbob]

I've heard you have to put a seal coat over any old paint or with included body work it's and extra cost but for yhe most part stop the shrinking pulling the old stuff ( paint apart ) otherwise a sand strip job is the other thing that stops that cracking shrinking . That aside "..it's worth mentioning when doing a 2 stage paint in hot weather maybe some lifting on a third heavy coat better to wait till ithe solvents flash Ed off even if it's 30 minets when doing a clear basecoat job .Nuthing like lifted paint to strip or sand and you have like 3 layers and 6 coats then the sealer starting over ?

 

[pagrunt]

Another thing is what was the humidity level. You have to have the right speed reducer based on temps & humidity. At 100 F there shouldn't be any painting.

 

[Rktpwrd]

Another thing is what was the humidity level. You have to have the right speed reducer based on temps & humidity. At 100 F there shouldn't be any painting.

This ^^^ for sure. Also the P sheets for the products you’re using need to be your bible. Exceeding the values and times they list and all bets are off.

That being said, it does sound to me like you went a little heavy on the number of coats. The flash and cure times are critical, and prep is key. There’s really no shortcuts you can take on any of these steps or you run the risk of having issues.

If don’t already have the P sheets for the products you’re using, I strongly recommend you do. They’re invaluable.