I am having a problem with my industrial painter, and I can't seem to figure out what it is. I have castings (cast iron) that are primered by the foundry with "Checkrust Shopcoat Primer" - AKP-363 Red. They are then machined by my company, and washed. Next they go to my painter where they are sanded, wiped down with thinner, and the particulates blown off. Then another coat of primer is applied - "Devguard 4160" in Red. Then the topcoat of "Centari" Acrylic Enamel is applied - in a variety of colors.
My problem is adhesion. The topcoat, along with the 2nd layer of primer is peeling off, literally in sheets, with hardly any effort at all.
At first I thought it was a preparation issue – my painter could have been taking shortcuts, but the more I investigate, the less likely I believe that to be.
My next thought was curing time for the 2nd primer layer. So we ran an experiment: One casting was primered and allowed to cure for over 48 hours before applying the topcoat. Another casting was primered and allowed to cure for less than 2 hours before applying the topcoat. The results were the same – both units peeled extensively.
When the paint peels, it is bringing the 2nd layer of primer along with it; leaving the original layer of primer nearly intact.
My thought is this: either the 2nd layer of primer is not adhering properly with the 1st layer of primer (a chemical incompatibility?): or the solvents in the paint are penetrating the 2nd layer of primer, causing it to separate from the 1st layer of primer.
Can anyone point me in the right direction? How do I find basic knowledge on paint: hardeners, accelerators, etc. Where can I find basic knowledge on paint types and compatibility: enamels versus urethanes, versus polyurethanes, etc?
I am a novice in regards to paint types or chemicals used, so any help that can be offered would be greatly appreciated.