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Old 08-09-2018, 09:29 AM
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Fiberglass body alignment?

I'm trying to get the body adjusted on my current project (fiberglass kit car) and feel like I have taken it as far as it can go with adjustment. Most of the panels fit ok and the gaps are pretty good, but there are places where the contours of the panels don't quite match up.

I can get the panels to fit well in most places, but there is no way to get the entire gap area to match the level of the adjoining panel. An example is the hood. The hood fits well at the cowl, most of the way forward of that and matches at the front, but there is an area just behind the front with a curve that does not match the curve in the body. No mechanical adjustment will correct this.

These mismatches are around 1/16", but a couple are about 1/8". I'm wondering what the best way to get these contours leveled up is? Can I just lay on some high quality filler or should I raise the low spots with a fiberglass based product (like Kitty Hair) and then cover with gel coat? Or is there something else I should do? 1/8" sounds like a lot of regular filler.

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Old 08-09-2018, 07:17 PM
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I use mat for that.. grind off the area to be laminated to with 80 grit.. clean with acetone and lay up the mat to fill the gap and it will not take much. then sand the gaps until you like them. Epoxy prime and some fill to make the part nice and paint. I would not use gel coat on an auto body as it cracks under vibration cracks to appear in the near future..

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Old 08-09-2018, 07:45 PM
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Thanks for the reply. I may not have stated the issue well. The hood is higher in that spot than the fender by about 1/8". Should I use mat for that, too? I've did body work on steel, but never did much glass work.
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Old 08-09-2018, 08:40 PM
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In this situation, the first thing I want to do is take away any material on the high side that can be removed without affecting the integrity of the part.

Next, I'd remove all coatings from the low side, and featheredge them outside the low area.

Then I would apply mat in severe cases, or use UPOL's "Fibral" if minor. Although this is about the only situation in which I consider reinforced filler to be an option.

1/8" thickness is the recommended maximum amount of filler after sanding, that most manufacturers suggest. Since the density of fillers is closer to fiberglass than steel, personally I would push that to 3/16" with trusted name brand fillers. No sweat.

The thing is, whether it is bare glass or reinforced filler... the entire worked area ought to be glazed with filler or 2K glaze putty. Not sanded through, and blended in where the featheredges of existing coatings start. Thats the gelcoat substitute layer, glazing putty.

After the fix, I find it much faster / cheaper to use a polyester primer for initial priming because the number of coats or applications of regular build urethane primer-surfacer is usually greater plus the poly primer seems to do much better with shrinkage over fiberglass repairs. It's density is closer to that of filler or glaze whereas urethane primer is closer to paint.

That comes into play on hot sunny days, later on. Unlike materials get a chance to squirm around when hot, and isolating your bare glass or reinforced filler with a layer or plain filler or glaze coat keeps "stuff" in the fiberglass from touching paint.

Not real technical, I know. But you don't have much misfit to address so theres not a great cause for concern in my opinion.
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Old 08-09-2018, 09:02 PM
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Thanks for the detailed reply. It was technical enough to point me in the right direction and gives me some good info to work with.

I would have probably gone wrong by not removing the gel coat.
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