Any Paint Experts in the House?

I have a question (or discussion) for a paint specialist; not so much someone who is good at painting cars, but someone who understands the science of paint adhesion and bonding especially the switch from solvent based to water based paints.

Some examples:





https://www.instagram.com/reel/CoDMH4WIHZ3/?utm_so...

https://www.instagram.com/p/CHXu46OF6Cf/?utm_sourc...

I don't know all the bodyshops, but one I do know of one as they are used by a well known Porsche indy.

Much of what you see here can be attributed to bad, or insufficient prep, but I've put a screen in after a bare metal repaint and about a year later the owner needed the windscreen replaced after it cracked from a stone strike. The same happened: paint peeled off with the polyurethane adhesive.

I think it's significant that some cars (especially Porsche) are not painted on the windscreen bond line. The e-coat is left exposed. Other cars don't do this. Could it be something to do with galvanised metal? If you dip or blast a galvanised metal car, what happens to that substrate when you repaint it?

Oh, really?

The bodyshell in the picture was ordered from Porsche. This is how it arrived; in colour. There was a masked line where the windscreen adhesive makes contact when you eventually come to fit the glass. I p[eeled that tape off. The connection to my original post is that it is clearly seen as a better substrate for PUR to bond to.