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The Chemistry of Rust Convertors

Rust Bullet

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Hello, greetings.

I am working in the paint industry and often-times come up with steel structure protection. Recently I have come across some waterborne acidic phosphate-type rust-converting primer recommended for cold-rolled steel and hot-rolled steel protection. This kind of primer is said to chemically react with any existing iron rust (Fe2O3. xH2O) and convert the rust into something else and hence stopping further deterioration. The exact surface chemistry is complex, but surely involves both the reduction of the ferric oxide and the formation of new phosphate layer with the iron. Its function is mainly as a tool for remedy, repair and maintenance of rusted steel, a "servicing" finish rather than OEM.

On top of this converting primer, a suitable solvent-based topcoat is usually recommended. My question is : How popular and how effective is this type of rust-converting finish on the steel protection business, and can you share more about its chemistry, its pros and cons ?

Thank you.

Benedict F [last name deleted for privacy by Editor]
paint manufacturer - Hong Kong, CHINA


Dear Benedict

Yes the phosphate coverts rust to iron phosphate which in turns retards the growth of rust. Its useful to use it when repainting old steel or even on new HR scaled steel. For 'bright' new steel I would prefer to clean and use a Zinc Phosphate Primer [affil link] instead.

Khozem Vahaanwala
Khozem Vahaanwala
Saify Ind
supporting advertiser
Bengaluru, Karnataka, India
saify logo


We are an outdoor light manufacturer, and one of our customers is buying this finishing in indonesia.

We would be also interested to do this finishing in China or have more details.

Zinc Phosphate Primer [affil link] seems to prevent rust, after cleaning the steel. But we are seeking reaction stopper after a certain degree of rust. Is zinc phosphate primer still the right reactor?


Samuel Puong
outdoor light manufacturer - Hong Kong

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