Options for cleaning and preserving underbody without paint?

[Who.Me?]

Hi

I have a '56 Single Cab that came from California but is now in the UK, so it's going to get wet more often than it has in the past.

The underbody and frame looks like this at the moment...

It has some light surface rust and still has traces of the original grey underbody paint.

I'd like to keep the rust in check and preserve the remaining OG grey paint, so want to avoid hitting it with a wire wheel.

I think I need a phosphoric acid product, followed by a clear preserving wax, but is that the right way to go in this case?

If acid is the way to go, do I just need to power-wash and degrease the underside before spraying with the acid? There's a fair bit of bondo dust stuck to the surfaces that I need to clean off.

Would I need to neutralise the acid, or just rinse after its done its job?

Can anyone recommend a rust converter/stabiliser product that will work on the underside without just dripping off before it's done its job.

Thanks

Andy

[beetlenut]

If you power wash it and let it dry, it will probably flash rust a little bit more. Then if you use a product that has phosphoric acid in it like Ospho, it will convert that rust to iron phosphate. BUT, when any of those converter products that have phosphoric acid in them convert the iron oxide (rust) to iron phosphate, they turn it black.
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[theKbStockpiler]

I Think your under side is a perfect candidate for sand blasting but I don't think your into a big project at this point. I have considered if the work of using plastic drop cloths to seal the whole car from the work area is feasible or not with my own projects. I'm going to try it sometime because intuitively I believe it is worth it. I'll stock up on a few rolls of tape. I don't think Power Washing is going to make a hill of beans difference or add more than 1/10,000th more rust to the area. For a temp fix Rusty Metal Primer has worked okay for me on moderately rusted areas that did not see a lot of rain and absolutely no salt.
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[Who.Me?]

Thanks for the feedback.

I thought you could wash the black gunk off with phosphoric to leave clean metal, so long as you don't leave it too long?

Stockpiler - I'm trying to keep the underside as original as possible, so want to avoid blasting/stripping where possible.

Upper body is another issue though. I'm told it was given a cosmetic do-over but that it wasn't stripped back to bare metal. Unfortunately the cosmetic job included a skim of bondo, so I doubt I'd get that back to the OG paint.

[beetlenut]

[far rider]

Probably not what you're looking for but have you considered oil undercoating?
I'm in Vermont where the roads are generously salted in winter. Used motor oil is used to undercoat cars. It is sprayed on liberally and holes are drilled in closed cavities, then capped, where rust is sitting. Messy? Very. Effective 100%. You could use new oil instead of used. Obviously not a "show stopper" but it would preserve the OG paint and your underside.
It would probably be easiest to apply. Anyway, just an idea.
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[eyetzr]

Some places have banned oil spraying, I was thinking wax. I am trying to find the info that was passed to me on a waxy type coating to put on bare metal for storage. I cannot find the info. I am sure if you can find it in the UK.
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I think he meant "rare", as in "not well-done"

[Bobnotch]

[eyetzr]

Thats the stuff. Yeah messy stuff, but does work well. We wiped off the excess & it kept the rust away. There are some other products the rat rod guys use as well. Penetrol, Gibbs, both oil products but for bare metal protection
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I think he meant "rare", as in "not well-done"

[Who.Me?]

Thanks again.

Beetlenut - understood. I'd seen pictures of clean steel after phosphoric cleaning and thought rusted steel would clean back to bare steel.

Having done some more reading around, I think I'm going to try a citric acid solution on a small area as I don't think it leaves a coating (although it may need neutralising?). Apparently mixing it with wallpaper paste makes an effective gel to cling to vertical and upside down surfaces.

I'm not trying to get back to uniform bright steel ready for priming, so it doesn't matter to me if it's not as effective as phosphoric acid.

It's also easy to get hold of in powdered form and cheap, so no loss if it's no good.

In terms of coatings, we've a few wax and wax + rust suppressor options over here from Waxoyl, Dinitrol and others, so I'll give one of those a go.

[c21darrel]

Your original pic looks very familiar.

I just spent the last 3 months under my DC sanding the whole thing front to back on a creeper. I had wanted to preserve my original primer and paint on mine too. I still have great og paint in the wheel wells too. All over was less surface rust than yours. I finally gave up that hope and decided to go down to clean metal with 80 grit and phosphoric acid. Then I covered it all w/ 2 coats of Masterseries, Im going to finish with light grey frame paint. And I am in So. Cal.
Good luck on your quest, If you can clean enough of the surface rust and dirt maybe you can wax it with heavy paste car wax.
Look into this stuff too, im not sure how long it protects.
http://picklex20.com/metal-surface-preparation/
http://picklex.com/
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