Saving a Rusted Car with Rust Bullet Paint and Cosmoline RP-342 Coating

Corrosion is estimated to cost about $250 billion per year in the U.S. alone, so it is economically significant. The impact of corrosion hit home for me when I noticed that near the bottom of the right rear wheel well of my little 2007 sedan, a 2-3” hole had rusted right through the metal, exposing some inner chambers to water and salt and sand thrown from the wheel. The rust does not look like it has compromised the vehicle’s mechanical integrity (a real concern, since today’s cars rely on the body sheet metal for strength), but if it keeps on going it could turn my chariot into a junker.

I called an honest local body shop, and the guy told me it would probably cost more than the car is worth to fix it properly (replace the rocker panels, etc.), and  it might run $1700 just to do a patch job.

Being a (retired) chemical engineer, I decided to read up on ways to deal with rusting metal. Especially, how to arrest the progress of rust. The most serious way is to do major surgery with cutting tools, and cut out all the rust, and weld good metal back in, and paint it all well. That is out of my league. So I looked for coatings that could stop the rusting progress.

I have written an article on a different blog describing the various classes of coatings and rust converters that are available. For my project, I chose to use Rust Bullet, ordered from Amazon.

This can be painted directly on rusty metal surfaced, after scraping away all the loose rust. This stuff chemically reacts with the remaining surface rust to make it more inert, and also forms an impermeable seal over the surface, to block further water and oxygen from reaching the metal. It sticks to rusty and non-rusty surfaces. It seems to get good reviews.

One peculiarity of Rust Bullet is that if many hours have elapsed after application its surface gets so smooth that that that the next layer of Rust Bullet or top coat paint will not stick unless you sandpaper the smooth, hard, silvery surface. It’s easiest, therefore, to leave only 2 hours or so between coats of paint, to avoid the bother of sandpapering.

After two coats of Rust Bullet, I applied a top coat of Rustoleum enamel paint (white on the outside of the car, black on interior surfaces).

Some rust had started on surfaces of the inner chambers of sheet metal that had been exposed by the rusted-out hole. I could not readily reach them with a paint brush to apply Rust Bullet. I wanted to spray something that would form a coating that would inhibit further rusting. I settled on Cosmoline RP-342, ordered from the manufacturer.

This stuff sprays on like a thick oily liquid, that should soak into any rust. After maybe 2 hours, it hardens up to a very impermeable, fairly tough waxy coating. It will keep water off surfaces, though I don’t know about oxygen. Anyway, I sprayed the Cosmoline into the available openings, to try to coat the surfaces of the inner chamber parts. (If I had known about it in time, I might have chosen Eastwood Internal Frame Coating instead of Cosmoline for this step.) I was able to coat most, though not all, of the vulnerable surfaces. This was all with me lying on my side, beside/under the car, without great ergonomic access.

I then used several layers of aluminum foil duct tape (learned this trick from YouTube) to seal up the holes in the car body, then added a final coat of white or black Rustoleum. This has pretty well protected the car body there from further exposure to water/sand/sand. It should give me a couple more years of use, all for two days of picky handwork plus the cost of materials.

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