[Shop-talk] Etching bare metal

[John Innis]

I often use phosphoric acid to clean and de-rust fuel tanks before coating
with an epoxy sealer.  I find it works great for getting ALL that last rust
out and etching the surface nicely.  As I am sure you recall, you must
clean and paint immediately.  Steel etched with acid will be highly
susceptible to corrosion if not coated right away.  I like to clean with
water to neutralize the acid then immediately rinse with solvent to get rid
of the water.  Denatured alcohol works great to dry the water, but might
not be compatible with all types of primer.

On Sun, Nov 13, 2022 at 3:31 PM Jim Stone <1789alpine at gmail.com> wrote:

> The last time I painted a car was in the 1980’s, which I’m pretty sure is
> before the invention of self-etching primer.  If it was around then, I
> didn’t know about it.  I learned everything I knew from reading DIY books
> and used a phosphoric acid solution to etch bare metal before priming.  I
> haven’t heard of anyone doing that anymore, but need to prime a trunk lid
> and am thinking it might be worth a phosphoric acid wash first.  I had the
> lid dipped about 10 years ago and it was left untreated all this time.
>  (Not by me, but that is a different and longer story.)  The lid has been
> sitting on the car and the underside still looks nearly perfect.  The car
> with has always been garaged but the top had a light coating of rust.  I’ve
> removed that now but there are some pits here and there (probably from
> before the dipping) and I would like to be 100% sure it is rust free before
> priming it.
>
> I have a gallon of this sitting around:
> https://www.amazon.com/Klean-Strip-GKPA30220-Gallon-Phosphoric/dp/B00945D15I
>  Is there any reason not to wash the surface with a diluted solution before
> priming?  Or, should I just use something like Rust-Oleum Rust Reformer (
> https://www.rustoleum.com/product-catalog/consumer-brands/auto/removers-and-chemicals/rust-reformer-spray/)
> and call it a day?
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