bubbles with e-coating over zinc plating

[marcellorossi]

Hallo collagues,
I would like to describe an issue to seek possible solution.
I have a tubular component, which is Zinc plated (12 microns) & subsequently has #Coating (25 microns).
We see some bubbles (or blisters) in the surface (see photo), and e-coating supplier says that it's due to too thick Zinc layer in combination to e-coating. He suggests to reduce Zinc to 8 micron, and the problem will disappear.
But final customer is asking to have 12 microns Zinc plating, and they are sure it can work, based on other similar items.
Do you know what is best practice to solve the bubble issue, in case of zinc plating + e-coating?

 

[WKTaylor]

Tubing metallic material is...?
Tubing surface preparation is...? per...?
Zinc plating type is...? applied per specification...?
Paint coating 'type/specification' is...? applied per specification...?

Regards, Wil Taylor

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[marcellorossi]

I was not able to get all these data from manufacturing guys.
However they told me that they found an issue with zinc layer: it was too big > 18 microns, when they reduced to 12 microns the bubbles disappeared.