New Project - First Time with Fiberglass

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PostPosted: Tue Aug 24, 2021 8:49 pm
Y'all were quite helpful with my TR6 project, which is wrapped up, or as wrapped up as any 45 British Car.

So I have purchased a 1981 Van Diemen Formula Ford (an open wheel race car) to take vintage racing. It's in wonderful mechanical shape, but the seller had an off in the spring, and the fiberglass got scratched up pretty badly.

I learned a lot on the TR6 (and a lot of what not to do). This is a race car, and will be chipped, covered in racing rubber, like run off track on occasion, etc. It's never going to run at Goodwood.

I'm no fiberglass expert, but I believe the black is gel coat not paint, and the red is paint. The scratches are through the gel coat. I may or may not go back with Black. I've got most of the logbooks, and may go back to one of the earlier liveries for the car.

Pics of the "before" and some pictures of the scratched pieces are attached.

I'm thinking single stage for the ease of repaint. But need some advice on prep before I shoot a primer and single stage. I'm not sure where to start because of the gel coat.

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PostPosted: Tue Aug 24, 2021 9:08 pm
my late brother-in-law use to repair fiberglass boats. i remember him spraying jell coat on the outsides of some of the boats they always looked good .
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PostPosted: Tue Aug 24, 2021 10:56 pm
With an existing open molded gel coat I like to sand with 400 wet or dry with a hard block. Epoxy primer will stick the best over the gel coat followed by your single stage paint. Before you start any sanding I'd make sure to do a good washing with Dawn and probably use a water based cleaner or a 50/50 mix of isopropyl alcohol and distilled water. Old gel coats like this can still have trace amounts of mold release/butter that can cause adhesion and fisheye problems. If you have any minor repairs to make I usually now just use an epoxy resin mixed with chopped up extra fine matt.
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PostPosted: Wed Aug 25, 2021 6:57 am
DarrelK wrote:With an existing open molded gel coat I like to sand with 400 wet or dry with a hard block. Epoxy primer will stick the best over the gel coat followed by your single stage paint. Before you start any sanding I'd make sure to do a good washing with Dawn and probably use a water based cleaner or a 50/50 mix of isopropyl alcohol and distilled water. Old gel coats like this can still have trace amounts of mold release/butter that can cause adhesion and fisheye problems. If you have any minor repairs to make I usually now just use an epoxy resin mixed with chopped up extra fine matt.


Darrel - That's super helpful. A couple of questions:

1. I've got lots of pre-prep left from the last project. Can I use that in place of an IPA/DI mix?
2. 400 grit makes a lot of sense to scuff the gel coat and give it some tooth for the primer. But some of the scratches are pretty deep and won't likely come out with 400. Given how flexible these parts are, particularly the main body section, I'm worried about just filling the deep scratches with filler. Both the nose and the main body piece get taken off the car regularly over the course of a race weekend. The nose has to come off to get onto the trailer for instance.
3. There are a couple of spots (stress cracks) that I will fix while I'm in there, so the idea of some chopped up mat, mixed in with the epoxy is a good one.



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PostPosted: Wed Aug 25, 2021 7:39 am
If you have to do a lot of repairs (and it looks like you do!), or knock down the gelcoat pretty far to get rid of cracks, then it's probably better to gelcoat it again, Though epoxy will work. You will have to buy a dedicated gelcoat gun, not expensive, and gelcoat (cheaper than epoxy, for use in filling). If repairing deep cracks, it's better to do them with cloth or matte, for a stroger repair. The chopped up 'glass is great for minor stuff.

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PostPosted: Wed Aug 25, 2021 7:57 am
Yeah, gelcoat is not a problem, just make sure it is a gelcoat made for air dry. Gelcoats designed for in-mold won't dry/cure properly. On those deep cracks make sure you V them with something like a Dremel tool. The bottom of the V must extend all the way to the bottom of the crack or they will come back later. Again, when you start doing any of this get stuff clean, clean, clean.... Oh, just noticed didn't answer your question on prep-sol. That stuff can bring oils/release agent to the surface without removing. The alcohol/water mix will dissolve and evaporate them instead.....
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PostPosted: Wed Aug 25, 2021 11:10 am
I may have over-sold the damage. None of visible scratches are cracks or in any way structural. But you can definitely feel them with your fingernail. There are a couple of areas near mounting points that have minor cracks (1/2") which is pretty typical in my experience with these old Formula Car parts. I have previously owned a similar vintage Reynard.

Never thought about spraying gel coat as I just assumed I'd sand down, prime and paint. I'll need to do some more research on spraying gel coat at the hobby / DIY mode.

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PostPosted: Wed Aug 25, 2021 12:39 pm
Great place to learn about gel coats and anything related to composites....
www.fiberglast.com Their learning center is a good place to start....
Metal, wood, fiberglass, we work it all... www.furniturephysicians.com We can restore the irreplaceable!



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PostPosted: Wed Aug 25, 2021 3:19 pm
being a racer and shop owner we do so much composite work from making complete bodies to repairing panels.
looks like you have a few cracks that need to be repaired.
to repair them grind down the area removing all the gel coating until you get to the fiberglass. do not try and glass over the gel coating at all.
you can for something like this use a cheap fiberglass and resin for your area home store.
the new glass will bond good to a 80 grit using anything courser than that is not recommended. you then can do a few lay ups of glass on both sides of the panel.
personally I would use woven cloth I'm not a fan of chopped mat for this type of repair.
a 6oz cloth would work good.
once you have a few lay ups done on both sides and the area has it's strength back to it it's most likely going to be a low area on the panel. this can be filler in with a coat or two of a body filler to bring the area up to level with the rest of the panel.
once the cracks are repaired you then can sand all the scratches out with 80 grit on a DA.
don't worry about sanding off the gel coat. if you have some scratches that are into the glass under the gel coat you can use a light weight body filler to fill them in. if it was a boat you could also use a firing compound but its a car not a boat so it should be submerged in water.
once your all finished with removing the scratches you can spray a few coats of a polyester spray filler ( feather-fill is a polyester spray filler) over the nose panel. there is no need to try and re gel coat the panel. again it's not a boat!
after the polyester spray filler is dry block it with some 180 and if need be you then can either spray two coats of a regular primer or sealer and going wet on wet from sealer right to your top coat color.
personally I like to spray two coats of a regular primer over the polyester spray filler.
the reason I like doing so is some times just going over the spray filler the finish isn't as nice because the spray fill is just a little more porous.
if your doing the black and red two color paint job on it I would just go with base clear. you can paint both base colors then just clear over everything at one time. by doing the black in single stage you would have to wait a few days then sand the area for the red and paint the red color.

when it comes to the itchy feeling from working with FG you can cover your arms and neck with baby powder. the baby powder will cover the pores of your skin.

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