Epoxy over Hot Dipped Galvanized 2

[dik]

I know there is a problem with zinc saponification with some coatings over a pre-galvanised material.

Is there a similar problem with the application of epoxies over zinc coating? I will check with specific coating suppliers.

Dik

 

[hokie66]

If the galvanizing is new, you will need surface preparation first, probably an etch primer or whip blasting. If the galvanizing is aged, this would not be required. As you are doing, best to check with the coating manufacturer.

 

[dik]

Thanks, Hokie... but I was hoping for some specific information about problems with epoxies and zinc coating. I've used vinager for a wash to 'kill' the surface with other coatings... but, I've not used zinc with an epoxy coating.

...it's part of a client coating spec and I want to vet it, personally before I accept this.

Dik

 

[hokie66]

I don't know about epoxies, but had experience with a proprietary space frame once, galvanized and coated with polyurethane. Already partly erected when we did adhesion testing, which failed. They had to disassemble it, take it back and remove the polyurethane, prepare the surface and recoat. Expensive lesson learned for the space frame supplier.

You are right to be concerned.

 

[SJones]

MIL-HDBK-1110, Clause 4.4.4

Steve Jones
Materials & Corrosion Engineer

http://www.oilandgaspeople.com/cv/11499664

http://www.linkedin.com/pub/8/83b/b04

 

[dik]

Thanks Steve, do you know of a link to the text? Doing a search, I get a connection failed type of message on any of links tried.

Thanks Hokie... not over yet, your comment is exactly the reason for my concern.

Dik

 

[dik]

SJones... found the book...

thanks, Dik

4.4.4.1 Epoxy Systems. Two coats of epoxy will provide longterm protection to galvanizing in interior service, as will one coat of epoxy and one coat of aliphatic urethane to galvanizing in exterior service.

Epoxy Coating System for Exterior Galvanizing Surface
Preparation Primer Topcoat SSPC SP 1 one coat MIL-P-24441 one coat MIL-C-85285 Formula 150 Type II
3 mils dft 2 mils dft

Epoxy Coating System for Interior Galvanizing Surface
Preparation Primer Topcoat SSPC SP 1 one coat MIL-P-24441 one coat MIL-P-24441 Formula 150 of desired color 3 mils dft 3 mils dft

Thank you, gentlemen...