[Shop-talk] Etching bare metal

[Pat Horne]

Several years ago I was stripping the frame on my 67.5 Datsun roadster using a pressure washer with a media blaster tip & was really surprised, not only how fast it stripped down to bare metal, but how fast it flash rusted. Within a few minutes of blasting, it rusted. I finally had to blast a minute or so, then dry & phosphate coat it before continuing. The phosphate I used needed to be washed off before priming which added to the process. Wish I could have found some of the phosphate that didn’t need washing but nobody stocked it. 

Peace,
Pat

Pat Horne 
We support Habitat for Humanity


On Nov 13, 2022, at 4:41 PM, John Innis <jdinnis at gmail.com> wrote:


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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