I have a 69 SS396 and I am having a problem stopping rust around the back window. Not long after I got the car I stripped the vinyl top off and the rot repaired by cutting it out and replacing with solid clean sheet metal then finished with a new vinyl top. Before the new top was done all the metal work was primed with PPG dp90, several years later it started rusting under the vinyl top again and had to be stripped off again, it was surface rust, but was making the vinyl top blister between the back window and deck lid. This time I used Dupont Vara prime and Euro prime, and have just recently noticed more rust blisters in the window chanel around the nail heads that hold the trim molding clips.
At least it hasn't been painted yet or a third vinyl top put on !!!
Any body got any suggestions on what to do to cure this problem for good
Thanks,Gene

Por15 in the window channel. I think there's an online article on this at their website, www.por15.com (http://www.por15.com)

Since you're using a vinyl top. I'd coat the entire area between the back glass and trunk lid. If you were painting, then you'd have to stop at the edge of the window channel since the only drawback to Por is that automotive finishes don't adhere to it very well.

POR-15 is great stuff. Can work here if you can topcoat to stick, I think they have a conversion coatoing for that. One additional option that most glass installers turn up their noses at. After all is done, clean rust por, or etch prime-epoxy prime-color coat, backfill complete lower glass area with w/s adhesive, The thick stuff, taper into pillars. lower glass area is a gutter with no drain, (not one of GM's finer designs) H2O sits there with no place to go. vinyl top is like a sponge holds and wicks moisture. Bed clips & mldgs. into adhesive. Be sure when vinyl top is installed that it is trimmed 1/8 to 1/4" around studs. Top has to be under mldg. (of course) but not down to studs. If you still have original studs they were welded to panel, tough to clean corrosion , if they have been replaced with screw in style, take them out, replace with new ones, after area is cleaned, brush epoxy or por in holes, screw in new studs, prep and paint. NOTE We have seen a lot of rust under vinyl tops in this area, appeared to be 2 causes. primed only under top or adhesive ate thru paint. ALWAYS paint under vinyl top and allow to be fully cured before top installed. I know the back fill idea sounds really mickey mouse and can make it difficult to remove mouldings later, but it DOES work. If possible always blow out water from around front and back glass areas after washing. otherwise will fill with dirt and NEVER DRY OUT! Karl

Karl, I have to disagree with the filling of the channel with sealant. All I have ever seen when this is done is much worse rusting. Invariably water gets under it and then it REALLY CAN'T get out!
If you want to fix it for good, put drains. I did this in my brothers '64 Riv and it worked great. I drilled a hole in each corner. Then got a two inch long piece of brake tubing, cut off with the flair on it. I dropped the tube through the hole with the flair holding it from falling through. Then tack welded it in and seam sealed it around the tube just like all the seams that are unwelded. I put a piece of vacuum hose on them and ran the hose out the bottom of the quarters. The last time I saw the car it was still looking good and the job was done over 15 years ago and the car has never been garaged!

I used to do a LOT of these windows being their was two glass shops within one block of my shop. After doing a number of them I think I came up with the reason they rust so easy. And if you think about it, I just may be right. The studs seem to be the starting point of the rust. They even will rust on the sides of the car where the studs are used for molding clips. I feel that the stud "head" shielded the base of the stud from the paint. That's right, when the paint gun, or robot what ever painted the car passed over the studs the head acted like an umbrella and the base was not painted enough. Hmmmmmmm

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1965 Buick Gran Sport Convertible
1965 Buick Skylark H/T
"Fan of most anything that moves human beings"

MARTINSR- Agree the drains are the BEST option. Have used mickey mouse (my words) method in past with decent success. Had lengthly discussion with our glass installer today. discussed urethanes, primerless urethanes, quick set urethanes, pinch weld primers, butyl tape etc. Will continue with his boss tomorrow & thurs. Not beating a dead horse, just want to know more. Will report back on qualities & adhesion characteristics. Thanks, Karl

DO NOT, I REPEAT DO NOT, "bed" the molding clips in anything! I just got done with replacing the vinyl top on my 69 elky and someone used this "method" previously... not only was there rot under the 14 gallons of goop, but the moldings wer basically IMPOSSIBLE to get off without totally detroying them. After buying a whole set of NOS moldings, digging 10 year old silicone gunk out from around the molding studs, and fixing the rust, the job is done... with NO additional gunk slathered in the channel around the molding... POR 15 yes, gunk around the moldings? definitely no.

I used por15 between the window chanel and the deck lid but not in the chanel itself, that was primed before the new top was put on,the por was used after the new top was taken off. What do you all think about removing the nail head studs and using screws to hold the molding clips on, I am also thinking of taking out the rear window and blasting the window chanel clean with a small sand blaster, then using por in the chanel. After the third top goes on, the car will be kept in the garage,( a sunny weekend car)
Thanks Gene

OK GUYS Let me try this again. Repeat, drains are BEST option. Keeping lower glass channel clean & free of debris is essential to longevity, with or without drains. Blow water out if possible. On these points I believe we ALL would agree? Is it safe to say we all would agree that if there is significant rust around studs, best option is to remove studs & replace with screws or screw in replacement studs, after thorough rust removal & prep. Refinishing of area can be done with product of preference.(por 15 base and compatable products or refinishing system of choice) Would like to restate my comments regarding overall refinish of entire area under vinyl top. Many undercoats will allow moisture transition to metal underneath if not sealed with topcoat. Vinyl tops DO retain moisture & can be a catalyst for corrosion. Make sure finish is WELL cured before top install. NOW the million dollar question. To fill channel or not to fill? If you do all of the above, NO further action should be necessary. Be really careful installing clips & mouldings as ANY damage to finish will allow rust to start all over again. <<<<MY statement BEDDING MOULDING was poorly chosen and can result with the experience Joey B described.>>>> Hovever, there are excellent primerless urethane glass adhesives available. One product is Essex #U-418 Quick Cure Primerless urethane. NO I don't sell it. It is one of the materials our glass company uses. I am sure there are other brands available. It will stick! Can be used to set glass or in conjunction with butyl tape. I would propose that SOME, SELECTIVE, use of this product will be a deterrent to future corrosion. DO's & DONT's Do use underneath & around clips. Don't fill to seal edge of vinyl top. If you choose to fill channel area to reduce volume of channel, start at bottom edge of glass & taper to clip, get as far up clip surface as you can with out contacting vinyl top. Do not fill to upper edge, covering vinyl top in channel or allow urethane to come in contact with trim moulding. Hopefully this retraction & modification of previous post makes sense. It will provide a reduction of painted surface being subjected to H20, reduce volume of potential H20 storage, provide additional protection around attachment clips. It will not create future service/moulding removeal problems. According to my glass company, this product adheres. With glass being a structural component of the newer cars it has to. Gene, if you use the car as stated and keep area clean & dry, backfilling NOT necessary. Getting rid of all corrosion & using flawless process to repair/refinish/assemble should suffice. REPEAT Yes, to stud replacement if rusted in that area. grind them off, do quality prep & relocate close to, but not in same spot. Just move em over a tad. You have many choices. Karl