Can someone tell me whats this is from?

[Jacksons Garage]

If your metalwork involved grinding, the grinding disc heats up the metal fragments which become hot, flying particles. The hot particles then come in contact with the epoxy primer and some are hot enough to melt their way through the primer and come in contact with the metal base. Some are just loose metal particles that rust.
If it were me, I would just scuff it and shoot it when ready. As long as you don't leave it exposed to the elements, it will be ok till you do so.
Always take the time to blow off surfaces once you grind anywhere around them.

[lyrikz]

***Ram-Man Re: My guess would be it sat too long after sandblasting before it got primer on it or if you primed it right away maybe you didnt get that area covered good with primer and humidity set in to cause the rust on the raw metal. ***

It did sit for quite a while inside the garage. THere wasnt any rust really but there was some light browning in that area. I just cleaned that up and coated over it.... It was only in one section of the cab. Is that where i messed up???

Originally Posted by 70 Suburban

Well if you did any grinding the flakes can embed in paint or even glass and start to rust....also are you sure you coated the corners well enough

I was sure i had at least a thin coat on it. Its always in the garage.

Originally Posted by cdowns

how did you clean the cab after blasting?

wax.grease remover, air. Just whateve rit took to get rid of the dirt.

Originally Posted by 67ChevyRedneck

Is that old sealant or new?

Its new epoxy. DP

Originally Posted by Jacksons Garage

If your metalwork involved grinding, the grinding disc heats up the metal fragments which become hot, flying particles. The hot particles then come in contact with the epoxy primer and some are hot enough to melt their way through the primer and come in contact with the metal base. Some are just loose metal particles that rust.
If it were me, I would just scuff it and shoot it when ready. As long as you don't leave it exposed to the elements, it will be ok till you do so.
Always take the time to blow off surfaces once you grind anywhere around them.

So overall consensus is, grind, or wire wheel the affected area and then recoat?

[mbgmike]

Thats fairly common in a crowded shop. Like stated above. We had a client refuse delivery on a S/Stl heat exchanger cause they said it was rusting and would not let it be unloaded. All it was grinding residue that rusted off another piece of equipment made from carbon steel that was close by before it was shipped. it was easy to take off but they should not have shipped it that way. Thats what it looks like to me from the pics.

[cdowns]

i find that when blasting with sand it is necessary to clean and scuff with something like rolac wheels or at the very least a scotchbrite pad to remove imbedded blasting media particles from the metal// wiping down with solvent soaked rags is not enough

[lyrikz]

Originally Posted by cdowns

i find that when blasting with sand it is necessary to clean and scuff with something like rolac wheels or at the very least a scotchbrite pad to remove imbedded blasting media particles from the metal// wiping down with solvent soaked rags is not enough

Ya, i didnt roloc it down.. I just cleaned it. ALSO, there was some browning in that section.

Im just going to wire wheel it down, grind it, clean it with some acid, rinse it off, then reepoxy over that particular area... Any other suggestions?