67 Camaro rear spoiler ... redo

Anything goes in the world of fiberglass and plastic



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PostPosted: Wed Aug 02, 2017 9:53 pm
In the process of painting my 67 Camaro I prepped the rear spoiler (which had been painted about 20 years ago) ... I sanded it down to remove most all of the previous paint leaving most of the old primer. I hit it with a coat of epoxy and 2k urethane then painted with acrylic enamel and got blister.

On further examination I discovered that the old primer from 20 years ago was not adhering to the fiberglass. The primer and paint was just a loose shell and could be lifted and peeled up in pretty large sheets. NOT GOOD!

I am scraping and sanding down to the bare fiberglass and will start from scratch on the refinish.

Memory tells me this spoiler would have only had grey lacquer primer on it, which is the main reason I am making sure everything is off before I start anew.

Once I am down to clean bare fiberglass is 220 grit sufficient to spray new epoxy and expect it to stick? I know on steel panels we want 60 or 80 to scar the surface. Fiberglass should scar easier than steel.

Once I get the epoxy on I'll hit it with 2K urethane within the recoat window.

Am I on track here? Any advice appreciated. I sure don't want this thing to end up less than wonderful this time.

I don't know a whole lot as I sit here today, but 20 years ago I knew a hell of a lot less :splat:

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PostPosted: Wed Aug 02, 2017 11:11 pm
Hmmmm.... are you sure that part is made of regular fiberglass? The way that peeled off is highly suspect. Almost sounds more like SMC (sheet molded compound). A sheet molded fiberglass part will look very much like fiberglass however it has a mold release actually right in the resin itself. SMC usually has a slightly "chalky" consistency as it ages. It is best sealed with full strength epoxy primer right on the bare surface. And I might consider dropping down to 180 for more profile. Since you're going over it with a 2k slightly rougher grit shouldn't be a problem for the epoxy/2k combo.
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PostPosted: Thu Aug 03, 2017 10:33 am
Thanks Darrel, I really don't know for certain what material this is. It does smell to me like fiberglass when I dry sand it, but with my knowledge that is not a sure answer to the question. I trust you more than I do myself.

Here is a PIC of the side that is completely stripped ... The core material is obviously light grey in color. *Looks like the dirt is in better focus than the spoiler*
Image
DSC_1329 by Larry Madsen, on Flickr

Here is a PIC of the other side which is in the process of being scrapped. You can see it is substantially covered underneath with the black factory coating that sealed the piece straight out of the box.


To my eye; I question whether this piece was even scuffed before that (now 20 year old) primer was applied way back when.
Image
DSC_1330 by Larry Madsen, on Flickr

There are a few places where the material is adhering better, but not many.

I have some 180 grit on hand, so I can hit it with that before I begin spraying.

I did not want to go too course for the strip on account of cutting top deep and deforming the spoiler.

Thanks for the guidance, if you have anything more I'd be happy to learn what it is ... but I'll proceed as you have advised.

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PostPosted: Thu Aug 03, 2017 11:04 am
Nope, that's not SMC so that's a good thing for you. Looks like a two piece mold of the wing itself with the outer shell being one piece and then the inner shell being molded separately. They then fiberglassed the edges together all the way around and ground those, shaping the edge just underneath. Might even have a foam core inside it..... That black you are seeing is probably a factory primer/surfacer. Since there has been obvious adhesion problems in the past the old prep. is definitely suspect. When you've got it pretty clean I'd do a water based prep. on it, dry for a bit, then go to the 180. Water based solvent degreasers are available from your paint jobber or just make your own with 50/50 distilled water and denatured alcohol. Wouldn't hurt to hit it with that again even after sanding.
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