What are you applying the coating to? and what coating material are you using?

Dik

Applying polyurethane wet paint to stamped SECC (electro-galvanized) steel.

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Mad Mango,
Are you using a primer on this ,or going with a one shot coat. I have not had good results with this , unless the electro galv is pre treated.
B.E.

You are judged not by what you know, but by what you can do.

The SECC is washed and oven dried, but there is no primer. The application looks decent, there was just a request for some standard on the drawings to allow for rejection of light/heavy application, orange peeling, etc. I have seen some PDFs online defining Class A/B/C surfaces (automotive origins I think), where A is a highly visible surface, B equates to side surfaces, and C are surfaces like the bottom and rear that are not normally seen by an end user.

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Many coating systems do not work well with zinc base... called zinc saponification. You have to find a coating that is specifically formulated for coating zinc based products.

Dik

What's the end application, i.e., outdoor/indoor, etc.?

In any case, http://quicksearch.dla.mil/ with a search for polyurethane pulls up a bunch of mil specs

TTFN (ta ta for now)
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Thanks for that search link IRstuff, I had it years ago, then lost it. One of those out of sight, out of mind things. This product is indoors, locked away in a closet or server room, in the dark.

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My main concern would be adhesion. Make sure you do adhesion testing. The kind where you make a cross with a knife, then try to peel it off. I'll leave it to you to find the details.

Hokie, the debonding of a coating from a zinc surface may take months to occur... and it may survive the initial test. Test is an actual ASTM Specification...

Dik

You may wish to contact US Coatings or SSPC. Both should have NACE representatives on staff to help steer you in the appropriate direction, though your initial suspicion is likely correct.

I'm currently deal with this same exact issue and I've found that I'm going with what dik has suggested; the ASTM D3451 standard. The ASTM D3451 is a guide covering the selection and use of procedures for testing coating powders and powder coatings and as such references many additional specific standards and guides the user to choose the standards most appropriate to their application.

You will always have problems with the coating if you are just washing and drying prior to application. The material needs pre-treatment (cleaner and phosphate).
Polyurethane should have no problems coating zinc......alkyds will saponify.

There may be a similar American publication. From my Project Notes:


ARCHITECTURALLY EXPOSED STRUCTURAL STEEL SHALL BE FABRICATED AND INSTALLED IN ACCORDANCE WITH AESS STIPULATED IN CISC CODE OF STANDARD PRACTICE

FINISH CATEGORY USED:
PROVIDE THE STIPULATED FINISH CATEGORY TO THE FOLLOWING ELEMENTS U/N:
ALL STRUCTURAL STEEL AND METAL FABRICATIONS: [AESS 1 | AESS 2]

AESS 2: FEATURE ELEMENTS VIEWED AT A DISTANCE > 6 M
SUITABLE FOR “FEATURE” ELEMENTS VIEWED AT A DISTANCE GREATER THAN SIX METRES. THE PROCESS INVOLVES BASICALLY GOOD FABRICATION PRACTICES WITH ENHANCED TREATMENT OF WELD, CONNECTION AND FABRICATION DETAIL, TOLERANCES FOR GAPS, AND COPES

AESS 3: FEATURE ELEMENTS VIEWED AT A DISTANCE <= 6 M
SUITABLE FOR “FEATURE” ELEMENTS, WHERE THE DESIGNER IS COMFORTABLE ALLOWING THE VIEWER TO SEE THE ART OF METALWORKING. WELDS ARE GENERALLY SMOOTH BUT VISIBLE; SOME GRIND MARKS ARE ACCEPTABLE. TOLERANCES ARE TIGHTER THAN NORMAL STANDARDS. THE STRUCTURE IS NORMALLY VIEWED CLOSER THAN SIX METRES AND IS FREQUENTLY SUBJECT TO TOUCHING BY THE PUBLIC

AESS 4: SHOWCASE ELEMENTS
SUITABLE FOR “SHOWCASE OR DOMINANT” ELEMENTS, WHERE THE DESIGNER INTENDS THE FORM TO BE THE ONLY FEATURE SHOWING IN AN ELEMENT. ALL WELDS ARE GROUND, AND FILLED EDGES ARE GROUND SQUARE AND TRUE. ALL SURFACES ARE SANDED/FILLED. TOLERANCES OF FABRICATED FORMS ARE MORE STRINGENT – GENERALLY ONE-HALF OF THE STANDARD TOLERANCE. ALL SURFACES ARE TO BE “GLOVE” SMOOTH

AESS C: CUSTOM ELEMENTS
SUITABLE FOR ELEMENTS WHICH REQUIRE A DIFFERENT SET OF CHARACTERISTICS THAN SPECIFIED IN CATEGORIES 1, 2, 3 OR 4

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