Originally Posted by JoAnnBortles
I have to agree with Ray. But there is no telling exactly what it is until you cut into one of the bubbles. I know you do not want to do that. But something is going on.
As for rust, metal is very porous, and sometimes rust can be deep in the metal, you grind and clean off the surface. It looks good and clean but underneath that rust is there and it will travel up to the surface once again. I know cos I went through this when I restored my 66 Pontiac Bonneville. 2 years later the rust returned and I was so sure I got it all.
So I have been exactly where you are. Gorgeous paint on my car and as it was a candy, there was really no way to spot repair it.
If you want to know exactly what's going on, you're going to have to dig into one of the bubbles. You can try sanding it down. Use a hard block like one of Motor Guards Run Blockers. I use these all the time in cases where I have to sand something out and not get to too far into the surrounding clear. Maybe you'll be lucky and they sand out.
Good Luck. Hope its not rust but I think it just might be.
Good call JoAnn, and thank you for adding, you are so right...it may not even be trapped moisture, it could be a rust spot from underneath and created a "pin hole" or as you said it may have been on the surface of the outer metal the whole time. If a person has been in the trade long enough and done enough vehicles, they know this is not an uncommon problem on vehicles especially older vehicles.
Usually in cases like this, moisture is the culprit that caused the metal to oxidize under the paint...when metal oxidizes it gives off gasses, these gasses cause expansion and they result in bubbles in your paint.
JoAnn, good to hear from you again, I think it's been awhile since I saw you last post.