Rust spots under old primer/paint?

[ncornilsen]

I'm only asking because I want to prevent this from happening to my SPI Epoxy when I apply it.

The area photographed shows bubbles in the paint itself, which turn into rust spots under the primer. the spots go away when sanded. I don't think any go through the metal. I don't know what type of primer this is... just that there is ALOT of it! I bought this hood used from someone who doesn't know its history.

These spots, and larger areas of flash rust, exist under the filler everywhere on the panel, even when the little blisters aren't visible.

Any thoughts?

 

[Jim C]

well you need to strip the hood completely, sand the metal so its clean and rust free. clean it and epoxy it. rust will only come back if its covered over

 

[elwood]

Difficult to tell from a phone screen, but to me looks like some of it might be water in airlines. Also could be water if cheap lacquer thinner was used to thin primer. Jim gave, as usual, the best advice.

 

[ncornilsen]

Difficult to tell from a phone screen, but to me looks like some of it might be water in airlines. Also could be water if cheap lacquer thinner was used to thin primer. Jim gave, as usual, the best advice.

Thanks guys!

I had no intention to leave a spec of that primer when im done, beleive me! I am just hoping to learn what caused that so i never do the same!

 

[texasking]

With SPI epoxy over clean metal, you won't have that problem. Hard to tell from that picture, but it looks like urethane primer over metal, which gives poor corrosion protection and adhesion.

 

[bill3337]

I suspect it may have been the old laquer primer that had talc in it, which was covered with a car cover and left out in the rain for an extended period of time. Eventually the water penetrates the paint by osmosis, right down and into the primer and you end up with hundreds of these little water blisters. Like they say above, sand to nice clean bare metal and epoxy right away. Should be fine in the end.

 

[Chris_Hamilton]

That type of rust also happens when applying body filler directly on steel in temps under 60 degrees. As the filler heats due to the catylization process against the cool/cold steel moisture forms and after a period of time you get what you have there. Always epoxy first then apply filler over the epoxy.

 

[Barry]

This looks normal for direct to metal primers and or lacquer primer or acid etch primer, all have a limited to metal life and the bubbles are co2 gassing from the rust.

 

[shine]

what there when start ....... be there when finished .

 

[Jim C]

what there when start ....... be there when finished .

there it is!! i was waiting for that post lmao!