Windshield / A-pillar. How tackle this, input wanted.

[Joarek]

Im restoring my 1985 Audi Coupe quattro and im well underway. This has been a learn as you go project and i had nada experience before starting with the car.
Im feeling more and more happy with my result, but there are various parts of the car i have avoided as i didnt feel confident enough.

So this is where i could use a little input on how to tackle this best. Here is my issue:







PS: only 4 images per post??

Ok, so my concern is the backside of my patches. The A-pillar got some sort of foam inside. Thats allright and no biggie.
But how would you make sure to treat the backside from rusting again? as there are no way to get "in" back there once the patch is welded in.

I got a donor windshield i will cut out patches from to get the right profiles and such without much hassle.

[Joarek]

Some more images:

[Len]

We would sand blast the area using a small spot blaster then cut back some of the metal around the hole until we are back to solid metal then weld in pieces of metal, grind smooth then apply a moisture resistant filler to finish the shape then prime and paint. Where the metal isn't rusted through we would blast away the rust and apply filler to level the surface before priming and painting.

[Joarek]

Thanks for the reply but i think you missed my question

But how would you make sure to treat the backside from rusting again? as there are no way to get "in" back there once the patch is welded in.

[Bob K]

I spray my patches front and back with Spies Hecker Priomat Primer 3255. In addition to being a direct to metal primer it is also a very good weld through primer. During welding a small area gets burned away. If there is no access point near by then it doesn’t get treated on the back side. I live with it. You can’t get everywhere.

My guess is that rust you are working on started on the outside under some chrome trim and spread over time. Am I right?

There is a wax you can spray on to the back side of a weld if you drill a small hole to get the wand in and I use that where I have welded on rockers or near the wheel well but not on something as high as the windshield.

Bob K

[Joarek]

Thanks for the great input. I will look for some wax protection and drill a small hole as you said, that seemed like a good idea

The rust started by trapped moisture under the window rubberseal i think. It might even have been due to a careless windowreplacement that scratched up the paint exposing bare metal (who knows).

Thanks again!

[Bob K]

I never do that on window openings. I paint the outside and leave the inside alone after I weld. There shouldn’t be any water in there. Chrome trim often scratches the paint and then rust starts because of the crack. That’s the way I should have said it. Just be sure to get good paint coverage on the window opening and then be careful putting the glass in and you should be good for a very long time if you remove all the metal that’s rusty now. Don’t spray any of that wax until you are done with your car. It can make a lot of problems of you get it on something you want to paint.

Bob K

[Len]

Thanks for the great input. I will look for some wax protection and drill a small hole as you said, that seemed like a good idea

The rust started by trapped moisture under the window rubberseal i think. It might even have been due to a careless windowreplacement that scratched up the paint exposing bare metal (who knows).

Thanks again!

Bob is right, that problem started from the outside and drilling holes and coating the backside probably won't accomplish much. Using good quality primer and paint will do more to prevent rust than coating the other side of the metal.