Cracked Paint Under Clear Coat

Maybe laquer/ enamel thing ? Have had same thing happen with a krylon base trying to cover with laquer........not sure why, but happens 2 or 3 times out of ten.......... stopped trying to fix..... now.sand everything off & start over with grey primer......
............. Peter

Never had one crack the paint but I've got one that no matter how much primer and sanding I do there's one spot on the roof that eventually bubbles. Might take a day may take a week but it always does it. I'm wondering if it's something in the resin.

Hey Eagle,

You and SKR have the right answers to this, there are a few ways this can happen.

Mixing Paint types: SKR mentioned using a Enamel base with a Urethane or Lacquer clear, he mentioned the exact reason why it happens... the enamel stays soft underneath and as the vapors try to escape the faster drying/hardening urethane/lacquer cracks appear. I try to never mix paint types or companies if possible, however you can use Acrylic base and a Enamel clear as long as you wait for the Acrylic to dry. try to never mix enamels, urethanes or lacquers. I have found that nail polish is perfect and cheap for these cars, most Testors paints cost about 1$ well the same is with nail polish but they come in a more vast array of colors, keep in mind finger nail polishes also come in enamels and acrylics. some are thick and if you use an airbrush thin them appropriately, on enamels you may use Testors " Enamel Thinner " to thin them out if you have to.

Mils: Paint has a max thickness that is allowed before having to completely let the " job " dry. This measurement is Mils or .001. Every paint has a max Mil spec. Now when using an instrument or gauge you have to think Wet or Dry Mils, Mils will decrease or "shrink" as the paint dries, from all of this you can see now why the above makes sense on why if mixing paint was performed than no doubt one of these lead to cracking. Try to keep your wet mils boarder line with the max preferred with each type of paint, primer is also measured in mils but isn't as closely watched in 1:1 painting because most is typically sanded off trying to make the body smooth... what ive noticed is people tend to use primers when painting their bodies and id just like to mention a few things on that part of paints.

You don't always have to use primer, primer is mainly a way to cause a small thicker layer of paint film on a body to help ensure that you have the body smooth. it does in some cases act as a sealer, when using bondo or other body fillers, fiberglass, epoxy and other certain body work fillers, primer is a great sealer but they also sell SEALER. One bad thing about primer is its thick... especially if you don't pay attention and grab a high build primer, this will greatly increase your mils and with the bodies we have for these cars its harder to sand that off. Sealer is great in the way it comes out as thin as a base coat... no heavy sanding needed and it will seal your base from your epoxies and fillers so they don't absorb your base. if you've ever had dry spots on your bodies and wondered why... that's filler absorption at work.

To simplify mils for those that don't have a gauge or feel the need to buy one, keep some key points in mind when painting. Don't put extra layers of primer/sealer than you absolutely have to, if you have two contrasting colors say black front half and white rear half only primer or seal enough to cover the offset of color difference. This should be no more than 3 light to medium coats. when spraying base, use enough base to cover the primer completely this should take about 3 medium coats, the base when wet on the car should appear the same as it does from its container... now saying that when paint dries some colors don't stay the exact same color they look when dry, this is due to the type of paint and how it dries.

Now to clear, Now I know many of you have heard the stories " back in 72 I had a 57 chevy bel air and it was candy apple red... 13 coats of clear, looked like you could just take a bite out of it "
The stories have truth to them but not why you would seem, back when base coat/ clear coat came out the chemicals we used wouldn't bond together like they do today, a trick painters would use to remedy this was to add more clear...MORE chemicals... this softened the base making the clear more apt to stick. how many people have seen a 90 model chevy truck driving around... some may own one... but the clear has come off in SHEETS almost. That's from the base and clear not binding to one another. Don't think more clear is better because its not...typically 2 medium coats and a wet coat is perfect, remember to leave your dry times between coats or youll end up with a nasty mess. if you have problems with grainy looking clear than it is too hot temperature wise and your clear is drying too fast. if its too cold outside ( with most paints under 60F degrease ) the clear will become cloudy and if left this way will remain cloudy. to get that sheet of glass look, clear is better to dry slowly but not too slow.

As for the " looked as if you could take a bite out of it "... also a painters trick, painters when " Candy Apple " was introduced played with the color... it was a bit transparent and they would typically spray a silver or gold undercoating with the red on top to give it the Apple color we all know today.

I know this is an old topic, but the questions seemed to be left in the air and everyones comments seemed uncertain so I figured I would fill in an answer as to why incase years to come there is someone to run across the same problem.

when painting always wear the proper gear, and paint in ventilated areas. this stuff is bad for you... Hope ive shed some light on this subject.

- Flat

I totally understand where youre coming from, i dont have alot of slot experience and i look to all of you guys for that. If i see something that i can actually lend a hand in ill do my best, i kind of figured by now you all had figured it out but from the outside looking in if someone ran across this i didnt want it to just be left to a maybe. I have a few things that ive been doing a while like painting, fabrication, welding, body work ect. Mainly mechanic and autobody stuff. If you or anyone have any paint questions fee free to send a message i dont mind helping at all.

- Flat