Letter 1126

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I have a question about galvanized metal... what are the best coatings for galvanized roofs (corn cribs) that have rust stains on them?

Arthur Brown
Painting by Brown's

The first question is whether they are *really* rusting or not. A powdery, scrapeable, dust, with corrosion pits below is indeed indicative of true rust. But areas which exhibit a shiny, adherent, brown, rust-colored stain are not truly rusting! Rather, this is just a phenomenon that often occurs in galvanized materials (due to intermetallic alloying I guess), and is not indicative of the end of the useful life of the coating.

In either case, the booklet "Painting Galvanized Steel Structures", available from the Zinc Institute, AHDGA or AGA (http://www.galvanizeit.org/publications/publications.htm) will answer all your questions in detail. Single copies are free, I understand.

 
Ted Mooney, P.E.
finishing.com - Brick, NJ

We live in Hawaii and are planning to repaint our galvanized roof. Do we need to prime the whole roof before painting or do we prime only the rusty areas?

gerri kahili
- Hawaii

"Rust Restorers" ? My question is, do they work and if so how do they work?

I have used one type in particular called "Extend" on my truck to try to stop some small rust spots from getting out of control and it apparently works because they have not spread since the application 3 years ago.("RUSTOLEUM" makes a similar product)

I was also curious to know if there are any similar products used to coat rusted areas of galvanized roofing prior to refinishing or painting to keep the rust from resurfacing?

Kevin Mott
- Newport RI

I have wondered what kind of paint do I need to paint my galvanized steel roof. Where can buy the paint.

RANDY BUI
- BERLIN, MARYLAND, U.S.A.

Unfortunately your question is vague, Randy, because you have not indicated the age of the roof or why you are painting it. If it's quite old and rusty, any outdoor paint designed for metal that you get in a hardware store is probably okay.

If it's a new roof it will still have a chromate conversion coating on it, which will definitely cause you adhesion problems no matter what kind of paint you use. You would need to remove the chromate conversion coating, which is a whole different story.

 
Ted Mooney, P.E.
finishing.com Inc. - Brick, NJ

I want to post a question or inquiry of my own.

 

I want to answer or follow-up on this question publicly

 

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