Any Paint Experts in the House?

[Glassman]

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.

[jeff666]

I have used both products,

Not really had a problem with either of them, just follow the TDS.

I do however prefer solvent over WB. What is your issue ?

[Glassman]

jeff666 said:

I have used both products,

Not really had a problem with either of them, just follow the TDS.

I do however prefer solvent over WB. What is your issue ?

If a car has had a bare metal repaint, and a windscreen is bonded to that fresh paint (long after bake/cure etc) something in the adhesive is attacking the paint/clear coat/bond and it lifts off. You never got this issue with solvent.

The painters I have worked with have paid extra attention to prep and we are satisfied that it is not a factor. It's something in the PUR and adhesion promoter.

We are now trying other methods.

Interestingly, a new bodyshell from Porsche comes with a masked line/area where the PUR goes which makes the acknowledgment that the e-coat is the best substrate?

[jeff666]

Possibly paint film thickness,

Do you know if the area affected was etch primed or epoxy primed before the primer ?

I have seen in the past when doing screen out repaints that the paint behind the glue can suffer from micro blister.

Sorry I can't think of anything else really.

[jeff666]

Oh and I guess this is water based we are talking about ?

[Bluevanman]

You might do better posting on spray painters group on Facebook.
Personally I've never experienced or heard of anyone else experiencing this issue.I was always solvent but I've got friends in bodyshops that are primarily water, and they've never mentioned having a problem.
I've also used a few screen fitters and none have ever asked what paint I've used

[paintman]

If you can identify the materials used when the vehicle in question was resprayed the go-to would be the paint supplier & the paint manufacturer.

Any comment from the manufacturer of the screen sealant?

[Glassman]

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?

[Bluevanman]

Looks like bad prep to me,shell gets primed,all outer areas get a good sanding/keying but the areas that won't get seen after refit,like the screen lips,just get a light scotch or nothing at all.
Top coats go on,screen gets fitted and all is well...... until someone comes along and removes the screen and the top coat comes away with the pu sealer

[paintman]

Bad prep or adhesion issues between the surface or the layers of different paint materials (primer, base coat, clear coat).

Certain bare surfaces - in particular galvanised & aluminium - really need a primer specifically recommended by the paint manufacturer for those surfaces or problems will occur.
No reason why the same primers can't be used on steel & many primers do cover the whole range.

[Bluevanman]

paintman said:

Bad prep or adhesion issues between the surface or the layers of different paint materials (primer, base coat, clear coat).

Certain bare surfaces - in particular galvanised & aluminium - really need a primer specifically recommended by the paint manufacturer for those surfaces or problems will occur.
No reason why the same primers can't be used on steel & many primers do cover the whole range.

Epoxy primer adheres to any bare substrate, it's what any decent restorer would use

[Glassman]

This is what a 992 bodyshell looks like from factory.

[Bluevanman]

Glassman said:

This is what a 992 bodyshell looks like from factory.

That's not screen adhesive.
That's showing primer,then sealer,then painted over with top coats

[Glassman]

Bluevanman said:

That's not screen adhesive.

Oh, really?

[Bluevanman]

Glassman said:

Oh, really?

How can it be if it's been painted over

[Glassman]

Bluevanman said:

Glassman said:

Oh, really?

How can it be if it's been painted over

I fit windscreens for a living.

[Bluevanman]

Glassman said:

I fit windscreens for a living.

And ?
If that's screen adhesive how come it's body colour?

[jeff666]

Bluevanman said:

Glassman said:

I fit windscreens for a living.

And ?
If that's screen adhesive how come it's body colour?

I'm guessing old screen cut out then paintwork done hence not seeing the cut marks,

I could be wrong as you would usually clean the screen adhesive back to bare before painting.

[Bluevanman]

jeff666 said:

I'm guessing old screen cut out then paintwork done hence not seeing the cut marks,

I could be wrong as you would usually clean the screen adhesive back to bare before painting.

You said it was a shell from the factory,not one that had been repainted.
Yes you would expect the bodyshop to remove that before painting.
From my experience it's usually a bugger to remove,it adheres that well it I've ended up grinding it off ......not done any 911's mind.

[Bluevanman]

Can you get installation methods off Porsche ?
They may use a particular brand of adhesive or primer.