I am repairing a very rusty lower windshield channel in my GP. There will be some areas that I can't really get at real well to clean up perfectly before installing the new windshield (nowhere near that point yet) but as I was working just now, I was wondering the above question.

Any windshield techs here? What will urethane stick to and what won't it stick to? I can ask the guys at work on Monday but I am kind of planning how this repair will go and have some different options to consider. The channel is pretty bad. I have to weld in a new piece for the entire bottom section that the glass sits against.

from internet

Two of the glass shops we work with have both said to not paint the pinchweld area, prime only. Also to scratch up the primer (epoxy or sealer) before appling the urethane.
Their concern as liablity with a failure of the paint layers to stick to each other or urethane to the primer.
This may be where the sanding recommendation comes from, I know they go to glass training classes.
With Butyl, which I haven't used for at least 15 years, I don't remember ever scuffing the paint. We used to spray Centari, Lucite, or clears and apply the ribbon the next day.

Something is lacking and/or the shop who is is doing my work and all the other bodyshops for 25 years needs to shut down or go to school. And they do insurance jobs. How does the factory install glass on a new car? Scuff the pinchweld first? The pinchweld with factory paint on a Jeep I just had done was not sanded prior to the glass installation. How about a freshly painted car at a shop with or or without baking? Scuff first also? No failures as of yet after all these years. I'm inclined to call them and ask if their procedure gives reason for concern. If a butcher prepped the factory paint poorly before painting it would matter little if it was scuffed anyway. The paint to paint is what would fail, not the urethane to paint.

pretty sure that stuff sticks to anything

I have found than nothing sticks to POR once it is dry.  POR makes an etch primer in a spray can that will stick to POR tho.

The windshield guys that really know thier stuff will not apply urethane to fresh paint or paint of any kind.  ONLY primers/epoxys.

I think if i was you i would treat only the rusty areas with por,  then before the por has fully cured,  like about 2 hours later,  apply windshild primer.  It is called pinch-weld primer,  its black and bites into amost anything. 

This pinchweld primer is what all the glass installers swab onto the body before they lay down the urethane.  Any glass installer will have it.

Best part for you is that it is black,  so you can swab it all over your window chanel and not have to worry about the color!

beaumontguru wrote:

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The windshield guys that really know thier stuff will not apply urethane to fresh paint or paint of any kind.  ONLY primers/epoxys.

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         What about new cars?   I thought they put the glass in after car was painted??

sorry i was off line carl, as a former winshield tech , no urathane sticks to any type of wet paint very well or for long, i did lots of rust repare in the shop from bad winshield installs, i would us a epoxy primer then paint then urathane primer then urathane. you also have to prime the inside of the winshield to protect the urathane from the UV light.their is clear primer and black primer use the black

i used to fix them with the small touch up bottles but spray can cnd tire works well it just has to be dry same as the urathane primer