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Ospho prep left tacky film

Q. I wire brushed, scraped, and cleaned some wheels off a 1980 Renault LeCar, which I think are galvanized steel, or at least zinc plated. I then sprayed on Ospho [affil link], which is a phosphoric acid solution, and waited overnight as per the directions. The rusted areas did turn blackish and seem to be ready for paint, but the clean, unrusted surfaces seem unaffected and have an uneven, blotchy, clear gloss film which is a bit tacky in spots. The directions say it will etch the metal, and leave a dry powder, but I see no powder at all. How can I tell if the metal has been etched? Has anyone else used Ospho on clean metal and what was the result? If I paint over the tacky film and the paint also stays tacky, I'll have a real mess.

Jay Proctor
- Lehigh Acres, Florida


A. Aren't you supposed to rinse before painting? or use a Self-Etching Primer [affil link]?

Larry Asche
- Gladstone, Oregon

A. Hi, Jay. Everything is a compromise, and I think Ospho "works" on galvanized steel but it's real strength is on rusted steel. Ospho suggests washing or wiping off the material after half an hour for nicest results on galvanized. In any case, I would now wait until it thoroughly dries, even if that is several days. Good luck.

Is there any chance that your "clean unrusted surfaces" actually have some sort of clear coat on them so the Ospho didn't even reach metal?


Ted Mooney, finishing.com
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

September 20, 2020

Q. I have painted Ospho on my aluminum garage door. However, after 24 hours it is still tacky. Am I supposed to paint the base coat when it is tacky or wait longer? Do I need to clean the door with mineral spirits?

This is my first project using this product.

Thank you,

Maria Clayton
- Dallas, Texas

September 2020

A. Hi Maria. Ospho is supposed to be usable on aluminum, so I'm not sure what went wrong. Is it possible that the aluminum has a clear coat on it such that the Ospho didn't reach metal but is just turning that clearcoat to gum?

Luck & Regards,

pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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