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November 7 - November 13, 2011

What is the best method for preparing newly galvanized steel to be overcoated with an epoxy system?



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Selected Answers

From Priya Samaroo of ftfarfan ltd on December 9, 2011:
It must be cleaned properly before applying an appropriate industrial coating. If the surface area has deposits, it must be cleaned with a heavy duty degreaser, and then you can use a direct-to-metal, water-based industrial paint.

From Adrian Granda of n/a on November 15, 2011:
     Galvanizing needs a lot of attention. Normally, you need a low profile to cover with an epoxy. I recommend  cleaning with SSPC-SP 1, then SSPC-SP 2 sanding with a sand paper number 100. Then you can apply a universal primer epoxy with appropiate adhesion to galvanizing.

From Kishore Kumar K R of Nukote on November 9, 2011:
     Degrease, then sweep blast to 20-25 microns.  Prime with suitable primer before applying an epoxy coating.

From Mohamed Ahmed of ELNG on November 15, 2011:
Hand abrading.

From boris vidic of CIS on November 14, 2011:
     Based on many situations on ships, I  recomended just a light sanding and applicastion of an epoxy holding primer. If you like, you can add a cosmetic final top coat.

From bichu rb of nsh on November 11, 2011:
     It's not required to blast galvanizing.  Just leave it if there are no defects. If there is any damage, we can touch up with organic zinc or surface-tolerant epoxy.

From frank crews of quality contractors and painting on November 7, 2011:
     Wash with a vinegar-water solution or use a light brush blast of the surface.

From James Albertoni of CA Department of Water Resources on November 14, 2011:
     Check out SSPC-SP 16. It's the new surface prep standard for galvanized and non-ferrous surfaces.

From William Feliciano of NYSDOT on December 19, 2011:
     Galvanizing may likely have been chromate-quenched to prevent white rust staining. Chromate is a definite adhesion killer. This must be removed. The point of brush blasting is to remove zinc oxides only, not to remove the galvanizing, only to etch it. Finally, allow no more than 1 hour between the brush blast/abrading and priming. Otherwise, zinc oxides will form again and impede adhesion. Polyamide epoxies are good primers. Apply at the lower allowable dry film thickness, then use a compatible topcoat. Why two coats? In our experience, pinholes and holidays in a single coat can allow moisture through, which will trigger the galvanizing to convert to oxides, which then blow out the paint system. I wouldn't paint galvanizing unless I absolutely had to. It's wise to wait two years (if you could afford that) for it to develop a zinc carbonate finish, which is very stable and a good substrate to paint.

From Carl Havemann of www.corrosioneducation.co.za on November 23, 2011:
    Degrease with a water-dispersible degreaser to 'waterbreak free' then sweep blast with garnet (fine grit), making sure the  blast operator is experienced. Can Lee tell us why he does not recommend abrasive blasting new galv surfaces ?

From Roy Bradley of Laing O'Rourke on November 17, 2011:
     It is extremely important to degrease new galvanized surfaces, which seems to have been missed by most respondents. After thorough degreasing, apply a mordant solution, then apply the epoxy direct. Alternatively, after degreasing, blast clean with a non-metallic abrasive to a profile between 20 to 30 micrometers.

From Lester Wienert of Wienert Mfg. Co. on November 14, 2011:
     Galvanized steel has good corrosion protection except in a polluted environment, where an epoxy coating may be in order. I have seen some aluminum paints actually cause corrosion - more than if there were no protective coating applied at all. I have had exceptional durability with properly formulated (corrosion inhibitor plus zinc dust ) water-thinned acrylic emulsion paints. Durability on iron water tanks is over 25 years now, and durability on galvanized steel quonset shows no peeling and very little weathering after 25 years.

From José Avendaño of Testers y Multimetros 2011 CA on November 11, 2011:
     Clean according to SSPC-SP 1 and apply a surface-tolerant epoxy primer.

From Lee Edelman of Independant on November 7, 2011:
     Galvanizing is a protective coating, and I recommend leaving it alone if there are no defects. If the specification calls for overcoating galvanized surfaces, there are several types of galv prep that can be used. I do not recommend abrasive blasting new galvanized surfaces unless specified.

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