mike77

So I'm shortly going to be taking out one of my rear quarters as I seem to have a leak. I can see a small amount of corrosion just peeping out below the window gasket. I may attempt some work on it.

My question is, would it not be possible to use a product like POR15 on the metal the is hidden under the gasket?

i.e. sand the hidden area back, use de-ruster and then paint with POR15.

I've never used the stuff but have read a lot of good reviews.

Chalkboss

Mike, I have used POR15 on a few cars and as long as the rust is not horrific it does a very good job at encapsulating it and preventing spread. They say you can slap it on untreated surfaces but I cleaned mine up with a wire wheel. Really good stuff. Of course this is a band-aid fix but it does work as advertised.

Mongo

I'm curious what would be classified as horrific? right now the rust bubble in my picture looks pretty damn horrific to me.

Chalkboss

I don't know (without getting into it) if your bubble is what I would classify as horrific. I would hesitate to use it on very thin, flaky sections that are structurally compromised. The parts I used it on were rusted and had some flaking but after I cleaned them out the remaining steel was still rusted but not too thin. Sort of a judgment call, but you will know more once you get into it.

dr bob

Horrific is relative. Telltales in your picture include the serious distortion/deflection/reshaping of the trim and molding from the rust growth underneath. That little blistering area you see on the outside of the panel is the first exterior growth of a cancer that's run out of good metal to consume in the window frame. Pull that quarter-panel cover on the inside, and see how bad the inside of the steel is there, where the rubber sits now. You'll want to get that panel out intact before it goes to a repair specialist anyway.

Mongo

Are you saying my whole quarter panel needs removal???

EDIT- Sorry. I get that the interior panel needs removal. Disregard.

I suppose if at worse, the section will need to be cut and a sheet metal welded in there. I was even considering the bondo patch.

Bill51sdr

Andy,

He means the interior panel...

Pull that quarter-panel cover on the inside, and see how bad the inside of the steel is there, where the rubber sits now. You'll want to get that panel out intact before it goes to a repair specialist anyway.

Makes sense!

Captain_Slow

POR-15 products are excellent... I've used their epoxy putty, POR-15 Patch, and POR-15 rust encapsulator on several Mercedes-Benz Unimogs. In some cases the POR repairs are stronger than the original metal (floor pan repairs). However, I was never concerned about it looking or being original - these were utilitarian Unimogs that I used off road on land to harvest wind-downed trees for firewood. In areas where I knew rust would return if repaired with new metal, I would view the POR repair as permanent. So in your case it depends on how much of your window frame is gone and how much you care to have it "good as new" (i.e. new quarter panel).

Our cars range from drivers to show cars. One has to decide what is acceptable.

If wire wheeling it reveals some pitting and small holes in the frame you could sand it down level (course sanding is better than fine as POR doesn't chemically adhere...it needs "tooth" to physically adhere to the surface...very important). After sanding and applying 3 thin coats of POR-15 (curing to a slight finger drag between each coat). After the 3rd coat cures to slight finger drag fill the pits or small holes with POR-15 PATCH. I'm a huge fan of POR-15 PATCH. It's POR-15 thickened in a tube. Great for sealing rusted seams or small holes. This kind of problem is exactly what it is intended for. I usually cut a shaped spreader from a milk jug or detergent bottle, trimmed until it matches the shape of the area I'm repairing. This gives a nice smooth application. When it again cures to a slight finger drag, prime it with the POR-15 primer (not regular primer). Then apply your topcoat at least 24 hours later. A weekend job.

NOTE: POR-15 cures rapidly in the presence of humidity (this is preferred...oddly) and slowly in dry air. So you have to work quickly and pour out only small amounts. A frequently opened can will harden solid due to humidity getting in. So I buy their six-pack of small cans. Don't put a lid back on a can after opening and pouring it without putting a layer of plastic wrap over the open can (otherwise the lid will not come off again).

If this sounds like a way you'd like to go you can PM for me information. OH...and don't get it on your skin...you will be wearing it until it literally "wears off".

The Fixer

Andy,

The other quarter window should also be taken out to check for corrosion before it creeps out of the channel.

This is smart while you're all set up to stabilize the rust with POR or
remove the rust the way i mentioned.

You will have to cut the seals with a utility knife to remove the glass.

I then bought used replacement seals from 928 International. Used seals
sometimes are better as the install easy. Mine seal very well.

I also didn't use sealant when re-installing the seals so i can check in on the areas every couple years.

Mongo

When I remove the windows (yes both since I see about 2mm of a bubble poking out in the middle of the panel on the passenger side too), I intend to drill holes in the lowest areas of the metal and coat them with anti-rust primer prior to paint in order to have any water from car washes drain. I won't be using sealant since I feel the holes will provide proper drainage. I believe that because Porsche used sealant, it caused water to get TRAPPED.

My seals look very new (this car was repainted sometime in the mid 1990s according to an old receipt), and I don't believe replacement of these seals are necessary. However, this DOES tell me that whoever repainted this car did not do any fixes under those windows, but merely slapped in new seals thinking the rust wouldn't continue to corrode.

Realistically, there is no way I will be able to tackle this project this year with a kid on the way.

upstate bob

@dr Bob, can't argue with your reasoning, just don't like to see the word "bondo" in repair methods. Since I hail from a place much better known for rust (Rochester,NY) than sunny Glendale, I do know a few little things about what works well enuff for reasonable success. BTW, if I ever paint my '79 I will not go the base coat/clear coat route, however shiny it may be. I prefer the old remelt single coatings that you can easily blend in when you do a repair. (done 'em both)

Hilton

Check posts 14 and 21, and 94 in this thread:

https://rennlist.com/forums/928-foru...-progress.html

Much more horrific than yours appears to be

Hilton

A local guy who parts out wrecked 928's told me he doesn't cut the seals.

He uses a toothpick to lift the seal edge and spray lube in around the seal, then pushes it out from the inside using a padded block and bottle jack, and a helper to grab the edge of the glass once it pops out of the seal at one edge.

I intend to try this as the rear seals on my 89 are in good shape, but I have a telltale spot of rust at the bottom rear corner peeking out from under a seal.

dr bob

I hail from down the road from you a piece. Born in Ithaca, of parents in grad school there. Migrated with them to NJ and moved on to California for the relatively cheap (at the time) in-state university system. And to escape the summer heat and humidity in the northeast. My little 356 cab suffered through the summer humidity and the winter cold for a couple years there before I convinced it to migrate west. Just a couple seasons, even with no winter driving at all, started the rust devils to work on it.

Fast-forward: We can see the ocean from here, but don't get any salt effects at 15 miles or so from the nearest patch ocean. When the daytime humidity exceeds 50%, I look for storm clouds. The 928 lives in climate-stable splendor here. Where Andy lives, his car is outside but under cover, and the condensation in the generally cooler weather he gets is more of a problem for outdoor cars. My 928 just passed its twenty-fifth birthday, Andy's is a little older. Lots of opportunities to have stuff happen in all those years. Amazing that they have survived, really. In perspective, my first car should have been a pre-WWII something, rather than a couple-years-old project. I sometimes wish I'd aged as well as the this car has.

Fogey1

http://www.bloxygen.com/
This stuff works very well for paint and tung oil and probably for anything that cures in the presence of air. Heavier than air so it forms a barrier. Maybe it'd work on POR-15.

IIRC, I once figured out it's argon, so a trip to the local welding supply place should get a lifetime supply cheap. OTOH, I have a lot cans I've used it on and I still have some in the spraycan. (Not that you can tell. Even full, it feels like its empty.)