Prepping surface rust for paint

JHZR2

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I had asked about rust-oleum type paints for outdoor/home use. Now I have a car application where I may want to use the same paint.

My new 1991 300d has a door lock vacuum pump under the rear seat. It is encapsulated in dense foam. At some point that foam was damp. It caused the vacuum pump motor to corrode, and caused some paint failure/loss of adhesion/surface rust under it.

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I used a die grinder and a wire wheel to knock off much of the surface rust.

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Now I’d like to prep and paint it. It seems like there was a surface adhesion issue because I was able to flake paint off to smooth primer in some spots.

What’s my best bet from here?

I was thinking ospho then prime and paint. Or even just ospho and paint. But since there is mixed bare metal and slight surface rust, should I do something else? Will self etching primer work here?

This is in a little well under the rear bench. Pretty isn’t important. But obviously I want to do a quality and neat job.

Any recommendations how to prep and paint this? Maybe even with white rust oleum that I have for other household needs? I think it would blend fine and nobody will ever see it anyway.

Thanks!!
 
3M Roloc rust buster type 3" wheel on a small angle grinder, you may also want 1 Scotch Brite disc to fine finish area.

An Etching primer would work fine, or more expensive Epoxy, followed by some Rust oleum paint.

If your going to use Epoxy, let it dry overnight before top coating, no sanding either type of primer. "If using Rust oleum in White, you must make sure you have all bare metal covered completely!

"Any" type of White pigment paint over bare metal will rust!" All White paints have Titanium Oxide, Titanium Oxide will grow rust on the topcoat If exposed to the Elements. That is one reason all solid colors on new Vehicles are clear coated, especially White!.
 
I would most certainly clean that up the best you can and look for an Epoxy Mastic type paint. They're very surface tolerant and very durable.
 
For the top coat I would use Rustoleum Professional paint. It very durable and is rated for industrial use. I have used it for several years and have seen what a great durable product it is.
 
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I have ospho and I have self etching primer. I also noticed that the Ace Rust Stop says that it can be sprayed direct to metal FWIW.
 
SEM, U-Pol and PPG’s OneChoice line has an aerosol acid etch primer if you can knock the rust down to bare metal, so does SprayMax with their 2K Epoxy primer.

Else, conversion coating is your best bet.
 
Get some good gloves and some red scotchbrite. Wet the scotchbrite with Ospho and goto town, and use various implements to get into corners better than your gloved fingers..

When the rust turns black, you can chisel it off revealing brown rust below, and Ospho scrub some more. Can do this to bare pitted metal if you wish to.

The Ospho will only lift the paint with rust under it. but will likely change the color of the paint to a lighter shade.

This method , thw whole area comes out amazingly clean, and adhesion of anything after that point is basically as good as it will get.

One can confine the area with masking tape first, perhaps something absorbent to catch potential drips at the tape edges, or plastic bags to keep ospho off the nice surfaces.

While ospho is super thin, it does not really evaporate. Apply thick on teh super rusty areas and leaving it on for 24 hours is wise.
There should be some white powder to remove before painting. The hair drier can be your friend, when time is not.

I've some rusty areas underneath, that are just not worth the effort to really treat properly.
I've just sprayed them with Ospho in a fine spray misting , and the rust is still black years later, even without painting atop it, much to my surprise.

Lung/eye protection vital when spraying it.
 
I worked ospho on the surfaces a few times. Essentially it was ospho-acetone-mechanical removal-ospho.

Finally I wasn’t getting returns.

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I had even chased under the seam sealer where more rust was lurking.

I decided to go with POR patch as the primer/sealant. This was for a few reasons

1) this isn’t a cosmetic area
2) por is designed for an acid prep surface
3) the car is galvanized, some is bare, some is OE primer, some is acid etched rust. I couldn’t find the right product that could do all three. POR patch seems to be compatible.

The biggest issue is that it is thick. It dries slightly flexible, but it’s thick. So getting it into the crevasse where seam sealer was, was a challenge. I tried to put a bead in there but working it in wasn’t very successful. I had a few air bubbles at the end, but I too coated it as I expanded the coverage. I have to do it sections at a time because there are many wires and vacuum lines passing there.

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POR patch is pretty well cured. A few soft spots where it was laid on thicker. I’m not concerned/opposed to those because it means that there is active product in contact with the surface.

I’ll cover it with white gloss paint and call it a year.
 
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