I got reproduction parts for my 53 f100. The black "primer" (?) on the bumpers (which have never been anywhere in the last eight years except my garage) is shedding in big flakes. The reproduction front fenders and valance also came with a black coating and that coating appears to be still holding on the metal. But, I'm a bit nervous about trusting that coating to be a decent primer for real paint in the next week or so. Anyone ever leave that factory black coating on reproduction parts with success? Or should I spend some time to brush off as much of it as I can?

 

Back in the 80's we would work on the company vehicles in the winter. We would get a lot of Taiwan fenders and such for the co. vehicles. All we did was hit em hard with a scotchbrite pad and put our own grey primer on and never had a problem, but then they weren't gonna be a nice old truck either. I'm sure someone with more modern experience will chime in. I got a repop fender for my daughters' Jetta a couple years ago and painted it with a puff can . It is still looking good. Wouldn't take much to sand it all off though as thin as it is. I think that is what I would do.

 

It depends on what your building. If your going to do a nice PPG paint job at $500-$800 a gallon a little extra prep would give me peace of mind. When in doubt, do a little extra.

 

What you are referring to as black "primer" is in fact "E-coat"...an electrostatically applied coating which should provide an excellent bond to the bare metal and protect it from corrosion. My experience with E-coats, from both US and offshore vendors, is that it performs as it should and when scuffed with some maroon or gray scotchbrite it will provide a good base for the primer/surfacers that I use. That said, any time that a paint/coating is flaking off then remove it all and start from bare metal with your prep before painting.
As a rule of thumb, if you sand the E-coat down until you see metal show through and the black coating does not flake or have a rough edge, then the bond is good. You should see a very gradual fade from black to silver...this applies to virtually all paints/fillers and is a great way to ensure that your primer and fillers are well bonded.

 

If it's flaking like you say that would tell me to strip it all off and re prime with good grade primer, problem solved

 

Thanks all. I am definitely taking the coating off the bumpers. Whatever it is, it wasn't intended to last. I'll take a close look at the other pieces.

 

Pictures would help but based upon your description I would agree with CharlieLed that it is e-coat. E-coat was never intended as a final coat and it is impacted pretty seriously by UV rays. It causes the bond between the metal and the e-coat to break down. If it has deteriorated as bad as you say you need to get it all off as it will continue to flake off. If you get an e-coated part it should be at least primed as soon as possible.

Your fenders may have been powder coated. OEMs dip clean, new bodies in an e-coat tank which coats the inside surfaces that never see sunlight. Then they rinse the outer panels with neutral PH water. After they go through a drier and while the bodies are still warm they are power coated by robots. Then it is back into the oven to be baked. When they come out they have a nice smooth surface with a strong bond between the powder coat and the metal body, ready for high quality paint.