Fibreglass questions - experience

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Fibreglass questions - experience

Postby CraigB » Sun 14 May, 2017 1:55 am

At times we have had people talk knowledgeably about fibreglass. Today i lined up the rear widebody panels onto a car and i've noticed that the flat edges, used to attach to flat panel, has actually warped a bit. I tried to pull it back in line but has dried in that position. Once fibreglass is old and hard is there any chance to bend it? Perhaps add some heat? What if i sand back some of the resin and make it thinner and then try and bend and redo gell coat and maybe some more fibre to strengthen?

And advice appreciated.
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Re: Fibreglass questions - experience

Postby kimrh » Sun 14 May, 2017 1:20 pm

Craig best to heat the fibreglass and clamp it flat and leave like that for a week.
When you attach the car with panel bond you will need to pop rivet it as well to make double sure it never lifts into the future
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Re: Fibreglass questions - experience

Postby CraigB » Sun 14 May, 2017 1:26 pm

so old gelcoat will respond to heat? That's the main question. I will heat the bog areas to get that off.
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Re: Fibreglass questions - experience

Postby merc-304 » Sun 14 May, 2017 1:28 pm

StreetBeast tech - Utube [bad audio]
Jalopy journal has a piece on it also..seems heat gun is the go ..and cooling with compressed air
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Re: Fibreglass questions - experience

Postby CraigB » Sun 14 May, 2017 4:51 pm

Sounds perfect, thanks. I can work it against the spare car and leave it sitting to mould better. Will screw it centrally and then work out gradually bending and screwing as i go. Will check out the youtube too.
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Re: Fibreglass questions - experience

Postby Bartman4800 » Wed 17 May, 2017 3:08 pm

CraigB wrote:so old gelcoat will respond to heat? That's the main question. I will heat the bog areas to get that off.



Craig,

Fibreglass resin is a thermoset plastic. It will NOT soften up with heat. It will only catch fire if it gets hot enough.

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Re: Fibreglass questions - experience

Postby CraigB » Wed 17 May, 2017 8:20 pm

So Bart, any theories why it has warped? Has it dried on one side more, although i thought it would have been hard already? Any suggestions what to do? Grind back some resins on both faces, hopefully weaken it and then progressively clamp and re-mat and resin on both sides to get straight? I have to have a closer look but i think it is just the edge that has warped and given the surface area, could possibly be trimmed back. Modern bonding adhesive and rivets should make a stronger bond than what it had.
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Re: Fibreglass questions - experience

Postby Bartman4800 » Thu 18 May, 2017 12:46 pm

After stating that the resin is a thermoset, I thought about it a bit more last night.

The actual fibers in glass-fiber are glass... And glass is certainly a thermo elastic material.

So while the resin will not do much with heat, the glass might.

Also, moist absorption might have played a role there too...


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Re: Fibreglass questions - experience

Postby CraigB » Thu 18 May, 2017 12:49 pm

Very good. Well i will have a gentle and cautious 'play' and report back!
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Re: Fibreglass questions - experience

Postby merc-304 » Thu 18 May, 2017 1:23 pm

Do you know if the body panels are made with polyester or epoxy resin.
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Re: Fibreglass questions - experience

Postby CraigB » Thu 18 May, 2017 6:26 pm

no - how do i tell? What were they using in 1982 in germany?
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Re: Fibreglass questions - experience

Postby Mercmad » Fri 19 May, 2017 10:28 pm

I would also suggest looking up this guys videos on fiberglassing and even send him an email. he has made parts for ALL of the big names in cars and boats.https://www.youtube.com/watch?v=oRBEEedpuRA Once a part is warped it would better to use the old part after it has been rectified as a mould to make a better part. messing with old gelcoat can get boring and expensive. (note: never buy glass supplies from Bunnings)
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Re: Fibreglass questions - experience

Postby AMG » Thu 25 May, 2017 5:35 pm

Back in the day the resin that was likely used would be an unwaxed polyester resin.

the reaction of the catalyst, and the resin actually melts the glass during curing process, and this is why the chopped strand mat can warp, and also why a mould is required. and why a part should be left for at least 48 hrs to cure in the mould. when a part blows out like that it usually means the resin was not properly mixed with catalyst before application, and may have cured too quickly - as the reaction is an exothermic one, the heat may have caused this fault during the wet lay-up process. It also happens in large spa's pools and fibreglass boat hulls when the woven roving is dispensed through a roving gun and the resin sprayed into the roving material. Occasionally time can get away and the resin starts to go off and comes out of the gun hot, and almost cures on impact with the mould. Cases like that are due to operator error, bad mixes, or too slow / mixed up too hot etc.

Heat will have an effect on a partially degraded GRP product, and the warping is more likely to be from the gelcoat in tension with the mating surface of the glassfibre resin. i.e. where you have 2 different rates of expansion due to different materials in contact via the mating surface.

Later resins have completely different flow and adhesive characteristics, some require catalyst other than mekp. in the case of repairing the old part, use a vinylester resin, instead of polyester. Or if you have plenty of $$$ use some aramid reinforced carbon twill, and R180, mixed with surfset, which will provide UV stability.
Bond your riveted seam to the panel with Sika 252 or similar, to ensure there is sufficient adhesion between the GRP and metal.
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