Molding FRP lip spoiler to OEM trunk

Anything goes in the world of fiberglass and plastic



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PostPosted: Thu Jun 06, 2019 6:07 pm
I hope I'm in the right subforum for this. I want to mold an FRP lip to my (of course metal) trunk. I don't have any hands on experience, but I have an idea. I don't think glueing the lip down and using bondo to smooth it out is going to work for me. I want it permanent and I want to do it right the first time. I'm fairly certain the bondo will crack if that's all I use.

I need a lot of help here

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PostPosted: Thu Jun 06, 2019 10:14 pm
Take a look at almost any manufactured vehicle with any type of "plastics" attached to it and you will notice none are molded directly on to metal. Why? The different rates of expansion/contraction of such dissimilar parts will almost immediately start splitting and cracking at the seams. So there is kind of a "workaround" for doing this.... I've done this a couple of times and was pretty satisfied with the look. I used premium painters tape and taped off the area where I wanted the spoiler. I then started to use Duraglas (short hair fiberglass filler) to build up the shape. Then layed up some fiberlgas resin and chopped up mat for a few layers and got my final shape. Then I just pulled the whole thing up off the tape and I had my new part. I then hollowed about an 1/8 inch cavity with a die grinder so I could insert a neoprene gasket. I drilled and fiberglassed a stud for each end and used that as my attachment points through the trunk.
I did have a buddy of mine that kind of went full tilt on his idea for doing a lip on his custom. He actually took a mold off his rear steel deck lid and made a "new" fiberglass lid which he could then simply shape his new rear lip into it. No dissimilar materials then, no problems.....
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!



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PostPosted: Thu Jun 06, 2019 10:58 pm
You're the same guy who replied to a thread similar to this 13 years ago, that's impressive!

Would 3M body panel bonding adhesive be a good alternative to the studs? What you and your friend have done are way more advanced than anything I can do right now. Is that the only path that would yield good results?

The approach I came up with before posting here was using the 3M adhesive to bond the lip directly to the trunk. Then.. Somehow mold it in with fiberglass. I'm not confident in my abilities to make a lip from scratch. I've only ever touched bondo to fill in low spots on body panels

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PostPosted: Fri Jun 07, 2019 7:26 am
Yes, the 3m adhesives or double sided molding tapes are good products. I don't like them a whole lot on lower sides of cars or lower front but for what you are doing they are fine. So you are thinking about using some type of stock lip piece, attaching it with a 3m product, then fiber glassing the seam to the trunk?......Yep, you could do that....just as long as you know it will fail.....when?, a week, a month, a year, but it will fail. I wouldn't even consider using a fiberglass for that....only thing that would give it a fighting chance would be something like West System epoxy with one of their filler/thickeners.
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!

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