Classic cars forum & vehicle restoration.

Rdover · Joined: 26 Nov 2007 Posts: 413

I am entering the last stages of my 1912 Alldays restoration which is all about painting the chassis black from the nasty orange colour used in the 1980s in South Africa.

Where I have surface rust or can remove parts to strip or bead blast there is no problem but what I can't do is totally dismantle to rid the car of every last vestige of orange.

What will happen if I acid etch prime over 1980s paint? Assume that the paint is well adhered, grease free etc but without its own layer of primer.

Cheers
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Richard

RobMoore · Joined: 16 Jan 2011 Posts: 105 Location: Peterlee

It will most likely react with the paint, however you can minimise and even avoid it if you apply very light dustcoats and gradually cover.
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Rdover · Joined: 26 Nov 2007 Posts: 413

Thanks
I'll go for the traditional sanding, and painting method for those parts I cannot strip entirely. That's my Xmas holidays planned!
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Richard

ukdave2002 · Joined: 23 Nov 2007 Posts: 4106 Location: South Cheshire

Hi , I have used acrylic etch primer over cellulose and 2k without problems, maybe try a small patch first. Barrier coats are availble if there is a reaction.

I also treat any bare steel whether corroded or not to a coat of 40% phosphoric acid, either brushed on or in one of those simple trigger / pump sprays, clean it off after an hour or so with panel wipe and prime straight away.

Dave

Rdover · Joined: 26 Nov 2007 Posts: 413

ukdave2002 · Joined: 23 Nov 2007 Posts: 4106 Location: South Cheshire

Hi Richard

Yep you are right, but the concentration of acid in etch primer is pretty low, fine for keying/bonding to newish metal, but I don't think it was ever designed to neutralise corrosion.

My approach may be a bit belt and braces, Shocked

but given £10 of phosphoric acid will coat a whole car shell, and doesn't add a great deal of time to the overall process I think its worth it.

When I painted my MGA, the body had been professionally acid dipped a few weeks earlier and dry stored, I gave the bare (and visually corrosion free) metal a coat of phosphoric acid prior to etch priming, and was quite surprised at the number of "darker" patches that formed. These were due to the acid reacting with what must have been early and not visible to the eye rust. I couldn't say whether the acid etch would have neutralised this, it may well have done as it was so light, but would be so annoying if paint faults occurred some time later.

Cheers

Dave