I have a 1978 Coupe De Ville, which may be my next project. For those of you unfamiliar with these cars, when they were built a flimsy rubber quarter panel extension sat between the very end of the quarter and the rear edge of the bumper. There a few companies that make a rigid fiberglass extension to replace the original part. Here is my question; is there a way to bond the fiberglass extension to the metal quarter panel, and eliminate the seam, so it looks like one continuous quarter panel? What I'm looking for, hopefully, is a method, and this is the important part, that won't crack at the seam of the two dissimilar parts. I've seen this done only one other time, and it looks so much better without that annoying vertical break in an otherwise uninterrupted very long quarter panel. The car sees very limited use, but will be subjected to the hot/cold weather cycle of Pittsburgh. Thanks, Mark.

The only problem I have found is in extreme heat (AZ/so. Cal), the fiberglass to metal joint can become visible. Once it cools back down, it usually returns to normal.

The easiest way to do it is:

1) Sand/Grind the metal to a 40 - 60 grit scratch with a nice cross-hatch pattern. Don't go nuts with the grinder, just enough to get a good "tooth" in the metal for the fiberglass resin to adhere well.

2) Sand/grind your fiberglass to the same grit as above. Get some fiberglass cloth (roving woven). Wear some nitrile rubber gloves.. Cut/tear some of the cloth into strips.

3) Get a couple of cheap disposable chip brushes and cut the bristles down to about 3/4" long.

4) Mix up some polyester fiberglass resin according to the instructions. "Butter up" the metal and the filler piece with the resin. Apply some of the strips of the cloth and use a paint brush to tap and dip into the cloth, pushing out the air bubbles. Keep dipping and tapping more resin in, making sure that the air bubbles escape. Brush it with a couple of coats of resin.

5) The next day you can sand and shape the fiberglass with regular sand paper or a DA sander.

You can use regular body fillers over the sanded fiberglass. If you need more filling, you can use a product like Duraglass or "kitty hair" filler.

That's the gist of it. There's a lot of ways to do it, but that is what I have done on fiberglass to metal joints.

im doing something similar and put epoxy over bare metal and topcoated within window some fiberglass filler.

i waited an hour this morning and then went to sand the filler and it started chunking clear off the epoxy

just so you don't mess up like me i'm not sure whats going on. i followed what the epoxy people said, do you have to wait past the epoxy recoat window for it to truly bond?

or are the epoxy people full of it and i should have used the filler instructions direct to metal with a 40 grit scratch?

you can use 3m 8115 and finish with kitty hair.

Dmac,

I am not a big fan of putting fiberglass filler over epoxy primer.
As a matter of fact, I don't even like to do anything more than a light skim of filler over epoxy. If I need to do any filling over 1/8", I properly prep the bare metal and apply it directly. I feel that plastic and polyester needs a good mechanical bond with metal, since it does not have any etching or penetrating qualities.

If I am filling over epoxy, I wait until the next day and skim it with something like USC Icing, MetalGlaze or DolphinGlaze (all 2 part).

I had a sheet matal shop bend and break me up a set once. That I welded in and final shaped on car.
Not for the faint of heart. Turned out great but I had a lot of time in doing it.

DURASPANK wrote:I had a sheet matal shop bend and break me up a set once. That I welded in and final shaped on car.
Not for the faint of heart. Turned out great but I had a lot of time in doing it.

Are you talking about the same car that I have? If so, what did it cost, and how does it look? I had thought of taking the fiberglass extension to a sheet metal place, but just haven't gotten to it yet. Of course that would be the best solution, because it would be permanent.

Roughly same year. It was 20 yrs ago though. Do remember it was 350.00 in the rough.

Metal and fiberglass expand and contract at different rates. You will notice this on hot days, a ghost line will appear. Whether or not that is acceptable to you is your call. Best bet is to fab up a piece out of metal and weld it in, but if your not familiar with the process you can do more harm then good.

i know this might sound crude, but if you did what vwhobby said and then skimmed the whole panel with filler, would it still gost where the metal and glass were joined??
or maybe attach the glassed piece, get it all smoothed over ready to paint, get a mould made of the whole panel and then replace the whole panel with a frp panel and bond it inside the doors openings where it wont be seen?? alot of work tho
krem