Although galvanized coatings are highly abrasion resistant, coating damage may occur once the galvanized steel leaves the galvanizer’s facility due to extremely rough handling, installation techniques, or in-service conditions. Occassionally, small areas of the galvanized article may be bare due to unseen contaiminants the cleaning process is unable to remove. There are methods available to ensure post-galvanizing coating integrity and ASTM A780, Standard Practice for Repair of Damaged and Uncoated Areas of Hot-dip Galvanized Coatings authorizes three accepted touch-up and repair methods:

  • Applying zinc-rich paint
  • Coating with zinc solder
  • Spraying with molten zinc (metalizing)

The touch-up and repair method chosen should consider the specific use of the galvanized steel and the performance characteristics of each of the three methods. Corrosion protection should always be the primary consideration, but certain uses and conditions may warrant selection on the basis of other performance characteristics. Applying zinc-rich paint is often erroneously called “cold galvanizing,” and may be appropriate for touchup and repair but just as is the case for applying any paint, surface preparation procedures outlined in D6386 should be closely adhered to in order to ensure the best overall performance. It is important to note none of the three repair methods provides the same corrosion protection as hot-dip galvanizing. 

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Comments

ahochstein@galvanizeit.org

J. Garcia,

Zinc-rich paint (often erroneously called “cold galvanizing”) is regularly used as a repair material for hot-dip galvanizing, but the AG does not have instructions for correcting the appearance of zinc-rich paint. Please contact the manufacturer of the paint product.

J.Garcia

Cold Galvanizing spray 2nd coat was applied a few hours before heavy rainstorm.  Water spots (dark gray color) appeared on the surface of the cold galvanized surface.  The water spots are not easily removed by rubbing with finger or damp cloth.  The water does not appear to have compromized the galvanized coating.  Is there a way to remove the spots without damaging the galvanized coating?

ahochstein@galvanizeit.org

Hi Slater,

Occasionally the American Galvanizers Association gets the question of whether the galvanized coating is adversely affected by exposure to fire, since temperatures can easily exceed 1,000 F. There is a potential for coating damage (peeling), but many have found fire damage to be minimal on galvanized steel. Often a layer of carbon dust coats the galvanized surface and under this layer the coating is intact.

The following article on our website that addresses what happens to hot-dip galvanized steel in extreme temperatures:
https://www.galvanizeit.org/education-and-resources/resources/technical-faq-dr-galv/galvanized-steels-performance-in-extreme-temperatures

Slater

Thank you for your expertise,

I have four Schedule 40 galvanized pipes supporting a solar array.  Recently. the entire assembly was damaged in the Napa, CA wildfire (10/2017).  I am trying to understand if (or to what degree) the galvanized properties have been compromised?  I have read that wild fires may reach 1400F.

Thank you,

Stuart

Kaycia Woolsey

I have an older galvanized pail that I am using for a vessel sink (in an old whiskey barrel vanity).  There are some small,  rusted spots on the bucket that I’m afraid will get worse since it will continue to get wet.  I was going to spray with Rust-oleum Crystal Clear Enamel.  It stays it stops rust, but it also says not to use on galvanized metal.  What can I spray or paint the bucket with to prevent the rust from getting worse?

Thank you so much!

Alana Hochstein

Mr. Hughes,

Often times it is required to remove some galvanized coating before welding, but these areas can be easily repaired after welding.  Please see the following page on our website about welding after galvanizing:

http://www.galvanizeit.org/design-and-fabrication/fabrication-considerations/welding

Mr Hughes

Is ther any one out that can help me I have got Sum fencing people doing my fence I am having a fence peace from my gate between to steel post instead of self tapping thay are welding it after it as been galverniced will damage it and is it going to rust please can some one advice me thank you

Alana Hochstein

Hi Heidari,

After a hot-dip galvanized item has left the galvanizer’s facility, there is no maximum allowable repair size specified within ASTM specifications.  Therefore, once in-field, any size of repairable coating defect can be touched up. For more information on acceptable field-repair methods, see our article on in-field touch-up & repair:
http://www.galvanizeit.org/education-and-resources/resources/technical-faq-dr-galv/repairing-coating-damage

HeidariNavid

Hi

My question is about permitted percent for repair/tuch up ,by cold method - for example zinka spray - at hot dip galvanized specimen?

Sincerely
heidarinavid
24-sep-2015

Hyder

Dear sir ,what is the procedure of un coated or damaged area painting

rejith kannan

have any solution for galvanzing inside pipe below 2” after installation of the pipe line?

B Dhayagude

Problem of rusting of galvanized angles of transmission towers: Normally @ 1 meter tower leg is open in air and remaining bottom portion goes in concrete foundation.  After @ 1 year the 3 components of foundation which are open in air are found rusted. These 3 parts connected to each other. (Tower leg, GI earthwire connected to leg and inside small angle). THe location of foundation is in the sugercane farm after the foundation was complete. What may be the reason of such rusting?

Daniel Barlow

O. Jones,

In a highly corrosive soil, using a coating over the hot-dip galvanized coating has been successfully used to increase the service life of the steel. Coatings such as a coal tar epoxy have been shown to produce great results

O. Jones

Galvanise steel cattle yards when lifted for maintenance have soil induced corrosion on the legs.  How does one treat this corrosion to prevent it happening again or at least increase the longevity of the panel?

g.appalaraju

Dear Sir,

my question is, is weld joints allowed in galvanizing pipeine. if allowed what about weld and adjacent areas of coating. for weld edge preparation both side coating has to be removed. i am asking about these area.

Regards,
G.A.Raju.

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