In theory...epoxy over flash rust

MikeS

Camaro Nut
I've done my share of removing old lacquer paint off factory panels and have seen very minor rust under some areas at times and yet there were no signs of it being under the paint from the surface. I have always thought that may have been flash rust from the factory during body assembly and the primer and topcoats sealed it from further rusting by denying it moisture or O2. Being epoxy is supposed to be so good at sealing metal, in theory, can it be applied over small traces of flash rust and stop it? I figure oxidation needs 02 and moisture to occur so if you seal it then rust oxidation should cease.
I don't spray over flash rust but I am just curious if epoxy can stop it if traces of flash did exist.

Mike
 
thats pretty much what I think when I hear about people obsessed with getting the e coat off of panels because they saw flash rust under some part of it.

E coating is done by hoist, alot of square feet at a time, so leaving a hot cleaner before it gets to the rinse, its bound to flash a little. You keep the moisture and oxygen from getting to it and it cannot grow. In my industry, we purposely put oxidation on parts to protect them. Iron phosphate on steel, chromate or anodize on aluminum. Then they dip those panels in a vat, charge them with current, and the coating fills every crack, crevice, void, spot weld seam it can get to. I dont think that flash rust is getting out or growing unless that e coat is disturbed. Those are chemical oxides and flash rust is simply an oxide. I say as long as its not loose the epoxy should stick to it and seal it..

When the epoxy manufacturer wants his epoxy sprayed on bare metal, thats what you do, but I dont think there is a manufacturer that will not think he will be considered one of the "snake oils" if he advertises to spray his product over any type of rust, even minor flash rust. They cant guarantee people are not doing it, they just take the blame when that epoxy fails, regardless of if the end user mixed it correctly, properly allowed it to burn in before spraying, or even gotten a heavy enough coat on the job.
 
Hi 'Another',

Sorry, I can't bring myself to write 'idiot' when addressing you so I'll just leave it at 'Another'. :)
I've used black oxide and zinc phosphate to coat steel parts and as you know they just require either paint or oils to increase the protection. But what does iron phosphate look like on metal when treated?

Thanks,
Mike
 
mikes;n82792 said:
hi 'another',

sorry, i can't bring myself to write 'idiot' when addressing you so i'll just leave it at 'another'. :)
i've used black oxide and zinc phosphate to coat steel parts and as you know they just require either paint or oils to increase the protection. But what does iron phosphate look like on metal when treated?

Thanks,
mike

lol!
 
Outlaw;n82795 said:

Depending on how much of the additives are put into it, its usually just a whitish powder with a tint of gold, which immediately does make you think of flash rust. I get a one dip product a local chemical shop makes that he adds extra molybdate to which gives it more of the blue tint, So Iron phosphate should be coated within 24 hours. Its a product I can use thru my powerwasher. Works better if you can heat it though.

Zinc phosphate is more dark gray but needs to be sealed with oil since its so heavy, so you are starting your job by removing mineral spirit residue with Zinc.it can last longer without coating, well, until you take the oil off. Black oxide, same deal, its only good as long as the oil is in place. Once that oil is gone it starts rusting.

I never want to confuse automotive painting with industrial painting, I just try to embrace what works. Most of the parts I do are military parts or marine types of coatings that are sitting out on or around salt water. So I never intend to say one way is better than another, its just when something works in the most corrosive environment on earth, well, also in space, it might have a use when coating the undercarriage of cars.
 
I have seen rust under E-coat bad enough hat it had compromised the adhesion-touch it with an abrasive and watch large chunks come off. I wouldn't want to put masking tape on an area like that LOL
 
Hi Bob,

In those cases where you have seen rust under the e-coat, I assume there were visible signs such as a rough e-coat texture to indicate there was something under it?

Thanks,
Mike
 
I think one item is being overlooked in this discussion. That is; it's really not about "e-coat" being bad, it's the improper application or substandard materials being used in the application of the "e-coat". I use quotes because I am sure there's many definitions.

Just like anything it's only as good as the person (or heck robot) doing the work. So rather than take chances or make assumptions folks just sand it off.
 
I dont know, the fact that its flash rust and not 10 year eaten thru rust is more of the point I think that is being made. It rusted in 40 seconds, was rinsed, went to the next step, got sealed in. No more moisture or oxygen gets to it, it will not continue to rust. When you put iron oxide on certain steel, it almost looks like flash rust. I think thats more of the point from the first question, sorry if I turned it into E coat, its just the procedure used its not like the parts are outside rusting in the rain and snow before the top coating is applied. We all know that e coat is just what they do in china and indonesia on automotive parts because they cannot ship them raw steel in the boats on the salt water. They are just selling it as a primer, but there are good things to it, mainly being an immersion process for full coverage.
 
after blasting a car i wash well with dawn soap . i bring them in and blow dry them right away. the flash rust is mostly iron deposits in the water . an orange tint does not bother me. and i have started removing all the ecoat now as many parts do not have ecoat on them just some bs black coating.
 
I heard what hey call e-coat today is not the same that was used previously. I have spare NOS GM fenders and door skins in the shed I bought back in the mid-80's and the e-coat still looks great with no signs of oxidation. One panel I bought in the 80's that I had to use had e-coat that was very hard to sand off.
 
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