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Ted Mooney, P.E. RET
Pine Beach, NJ

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Removing white spots / storage stain on galvanized metal

2002

Q. Hi,

I am wondering if I have an arguing point with the galvaniser over white rust that resulted to black marks on the galvanized surface. As I recall from an article from finishing.com, white rust occurs when the zinc corrodes. And I believe it does rust on these black spots or marks. Right? The galvaniser is telling me that it's something they can't control. The black marks are giving the parts poor appearances.

black spots on galvanizing black spots on galvanizing2

Where I come from - Malaysia, many users are not at all initiated to understand coatings/finishing. Is grinding on galvanized parts to get rid of 'teardrops' from the galvanizing process acceptable/allowed?

I would be grateful if you could give me your opinion.

Thank you.

Regards,

Jeremy Yap
- Malaysia

"Hot Dip Galvanizing of Steel Structures"
by Kuklik & Kudlacek
galv_structures2016

on AbeBooks

or eBay or

Amazon

(affil links)

"Handbook of Hot Dip Galvanization"
by Maass & Peissker
galv_hot_dip_handbook2011

on AbeBooks

or eBay or

Amazon

(affil links)

A. From what I can tell of the pictures the bundles of material appear to be tightly packed and outside. If they are stored flat, any moisture would be trapped on and throughout the material. This causes a chain reaction that can attack the galvanized coating. If you have black areas it is probably bare. If you have areas that are white in color you can brush it away with a wire brush and check for readings with a magnetic gauge to see if it is bare steel. Bundles should be stored inside if possible, but at least stored at an angles in a bundle that is spaced in rows to allow any moisture to drain away from the material.

If you have spikes or "teardrops" they can be evenly filed away without effecting the coating. If you get down to bare metal you will need to repair it with a good cold galvanizing compound Cold Galvanizing Compound / Zinc Rich Paint.

Mike Stroia
Gregory Industries - Canton, Ohio
2002

A. You can ask your supplier to coat the galvanised sheets with some special rust preventive to prevent this white rust formation. I know a few products used successfully in galvanised products for controlling white rusts.

Indrajit Banerjee
- Kolkata, West Bengal, India
2002

A. Hello,

The black spot on galvanized surfaces is commonly called corrosion etching, apart from other factor, aluminum concentration needs to be controlled, drying condition has to be improved and use of PWG grade zinc will help to minimize the formation of black spot. use of certain percentage of tin--<1.3% and antimony < .05% will help to beat the problem of black spot.

Mahbub Hossain
Galco Steel(bd)LTD - Narayangonj, Dhaka, Bangladesh
2002

Multiple threads merged: please forgive chronology errors :-)

The effect of rough white spots on galvanized steel electric masts on durability

Q. One contractor has delivered to the site (which is sea port site) a number of 30 m electric masts made of galvanized steel. These were stored near the sea raised on wooden platforms by half a meter. White rust has appeared. Some spots of the white rust areas are rough in texture whereas the other parts of the white rust areas are smooth like the rest of the galvanized steel areas. Measurement of the thickness of galvanization on all spots gave higher results than required. The thickness at the rough spots seems to be more than the rest of the white rust spots. I am concerned about the rough spots. The contractor as well as the material supplier and factory engineers suggest applying a rich zinc paint after cleaning with special chemicals. Please advise of the effectiveness of the proposed treatment.

Dr. Jamal Omari
Ministry of Municipal Affairs & Agric. - Doha, Qatar
2004

A. This white rust is probably also what is known as "wet storage stain" and results from damp parts not getting enough fresh air to form corrosion-resistant corrosion products. While I can't say if these parts are satisfactory or not, I can note that wet storage stain usually isn't nearly as serious as it looks because the corrosion products are so voluminous compared to the amount of zinc that was actually consumed to generate them.

If you search this site or galvanizeit.org for "wet storage stain" you'll find some further input.

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

White Rust treatment

Q. I have a lot of galvanized angles, shipped from North America to Indonesia. All of them have White Rust on them. I need to paint them with an Acrylic Latex and am looking for information on surface prep. I have tried pressure washing, Scotch Brite pads with water, wire brushing. I am wondering -- once the white powder is removed is the White Rust process stopped -- or will it continue on, under the paint? thanks.

Kermit Severson
consumer - Surabaya, Indonesia
2005

2005

A. Painting hot dip galvanized steel is not an easy task and I have no direct personal experience. A friend in South Africa had a truckload of galvanized pipes that white rusted and he effectively used dilute acetic acid ⇦this on eBay or Amazon [affil links] (vinegar) to clean them. In Northeastern USA a company routinely paints FRESHLY galvanized product and has a trade name for this product. I doubt they would share their technology. In the proceedings of The International Galvanizing Conferences (a series of books) there are several technical articles on painting galvanized products. Also the series of books "Zinc Abstracts" there are likely references to painting and pretreating galvanized steel for painting. There may be a limited number of paint companies with knowledge of pretreating and painting galvanized product.
Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA

A. PREPARATION OF GALVANIZED SURFACE IS NOT AT ALL DIFFICULT; CHEMICALS FOR REMOVING SUPERFICIAL AND CHEMICAL IMPURITIES ON THE GALVANIZED SURFACE, AND FOR FORMING ZINC PHOSPHATE COATING ON THE SURFACE ARE AVAILABLE: SPRAY PROCESS OR DIP PROCESS.

S. MEENAKSHISUSNDARAM
- CHENNAI, INDIA
2005

A. I have achieved a measure of success at my seaside home using a locally produced product made by a local company called Plascon. they sell a galvanized iron cleaner that is scrubbed on using scotch brite pads, rinse well with clean water and allow to dry. Prime with a coat of their yellow galvanized iron primer. Then two coats of Wall and All. The two latter products are water based. I used this treatment on new iron railings around my property about 4 years ago and they are still looking good. I have no connection whatsoever with Plascon company.

Peter Flicker
Retired - Cape Town, South Africa
2007

Q. If I use white passivation and white rust still formed where is the problem and bad storage can lose the passivation effect, if white rust formed on pipes how could I remove it easily?

Mouhmad Hammad
asp - Jordan
2006

A. Sir:
About 20 years ago an industrial friend in South Africa told me how he cleaned a truckload of white rusted hot dip galvanized pipes using vinegar ⇦in bulk on eBay or Amazon [affil links] toothpaste and light sandpaper. Nothing has come off. Please help. How do I remove them. Thanks for your response.

Lynda Dunn
- Mount Pleasant, South Carolina
2006

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Ed. note: No pic was attached in your e-mail titled "Graphics_for_Letter_46161", Lynda.

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