I cant tell you what causes it as i never got to the bottom of it on my old mk2 granny but the fella that painted it for me reckoned it was a reaction to the old cellulose(sp?) paint allready on the car
Mine started off with a few small blistery bubbles on the bonnet and wings and i was told the only way to stop it was to go back to bare metal. The problem was after being in the oven having the front painted again, other problems appeared like micro blisters and cracking on other previously unaffected parts of the car.







fucking soul destroying when you spend so much time and money on something and this kind of shit happens.