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Mazda Paint Bubbles

2002 Mazda Protege. A couple of months ago, I noticed numerous smallish bubbles – a quarter inch to half an inch – in the paint on both rocker panels. Drat, I thought – rust. But it turns out that the bubbles are full of clear liquid – water I think – with bare, shiny steel under the water. The “paint” is thick and rubbery BTW, I think it is not ordinary body paint.



Anyway, since new bubbles keep on appearing, my plan is to strip both rocker panels to bare metal, then prime and paint them.



But I am kind of curious what is going on. How is the water getting under the paint? And why doesn’t it have enough dissolved oxygen to put even a film of rust onto the rocker panel metal?

I’m gonna take a wild, wild guess. I may be totally off base. I may even be crazy.

Modern automotive primers and paints are water-based. And many manufacturers use a special coating on the rocker panels designed to prevent chipping.

i’m gonna guess that the paint topcoat on the rocker panels was applied over wet primer, the paint cured faster than the water in the primer was able to migrate out, and you’re seeing the water that has actually originated from the primer.

Rust is iron oxide. Being sealed off from the air actually probably prevented oxygen from getting to the spots and prevented rusting. The oxygen in the water is tied up with the hydrogen, and unless the hydrogen can escape it’ll stay that way. That’ll prevent the formation of iron oxide.

Its probably a product called Rocker Schultz or similar which is a plastisol type product that remains pliable and guards against rock chips. The rockers are probably galvanized which is why there is no rust if in fact it is water under there. If you sand it, you will likely go through the galvanized coating and it will be prone to rusting. I can’t believe there is water under there but I think I would just have a body shop take a look and see what they think then go from there.

Thanks guys. I can’t believe that there is water under there either, but there is some liquid that is colorless, odorless, and not viscous. Water seems the most likely candidate.

I hadn’t considered the possibility that the metal is galvanized. It could be. On the other hand, the bare metal rusts pretty quickly once the bubble is taken off. In any case, back when they made cars out of metal, didn’t we routinely sand repairs to bare metal, prime and paint them without undue rust damage to the area repaired?

You are correct. That is the correct way to repair paint and/or surface rust problems.