Weird fiberglass panel issue

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Weird fiberglass panel issue

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raygun	r raygun posted 4 Years Ago HOT Topic Details
r Group: Forum Members Posts: 22, Visits: 126	I'm getting ready to make a mold from the hood of my 2011 Corvette. When I bought the car in April, it had a weird matte vinyl wrap on the hood. When I removed said wrap (ugh), I found an odd grid of what I thought, at the time, were scratches. Since I've finally found time to get started on the planned carbon hood with some heat extraction, I took a closer look at the hood. These don't really look like scratches so much as CSM. They also line up with the reinforcement on the bottom of the panel. I cannot, for the life of me, figure out what could possibly cause this. I posted a question on one of the Facebook groups. It turns out that a lot of Corvette owners have this issue, in the pattern and same places on the hood. Someone suggested that it may be related to heat from storing the car in direct sunlight. That strikes me as weird. And on someone else's car: I love the car, but... lovely GM quality strikes again. Any ideas what could cause this? Also, I'm worried that buffing and preparing the surface may just make it worse. I'd appreciate any advice y'all might have as to cause and possible solutions. I'd really like to clean this up before making a mold. Edited 4 Years Ago by raygun
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Warren (Staff)	Warren (Staff) posted 4 Years Ago ANSWER Post Details
Group: Administrators Posts: 2.5K, Visits: 7.9K	Sounds like print through. Thin gelcoat maybe, not enough tissue or thin laminate before the thicker chopped strand mat. Sometimes curing issues can make it worse - eg demoulding too soon. Could easily be possible in an OEM manufacturing system if someone was not too hot on the QC to end up demoulding like that. Also heat cycling of a resin that isn't quite post cured enough. You may end up having to skim the surface in something to smooth it out if its really bad, although if you make the mould with a thick gel, then you should have some sanding/polishing room to correct it. Warren Penalver Easy Composites / Carbon Mods - Technical Support Assistant
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raygun	r raygun posted 4 Years Ago HOT Post Details
r Group: Forum Members Posts: 22, Visits: 126	Given the other issues I've had with this car - cross-threaded brake fittings, horrible welds, etc. - I'm not all that surprised. The orange tooling gelcoat I've been using goes on pretty thick. Smoothing this out in the mold rather than potentially further damaging the hood sounds like a reasonable approach. (The hood looks bad, but not as bad as it could!) At least if I screw it up, I'll only be out $30 worth of materials rather than a new hood. Cheers and thanks for your time! Edited 4 Years Ago by raygun
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Hanaldo	Hanaldo posted 4 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	It's print through from where the inner skin is bonded to the outer skin, the adhesive will cause distortions like this. Actually even occurs on metal panels, if you look closely enough at most cars with bonded panels (roof being the easiest to spot) you will probably find where the adhesive has creased the sheet metal.
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raygun	r raygun posted 4 Years Ago HOT Post Details
r Group: Forum Members Posts: 22, Visits: 126	+x Hanaldo - 11/19/2020 9:00:14 PM It's print through from where the inner skin is bonded to the outer skin, the adhesive will cause distortions like this. Actually even occurs on metal panels, if you look closely enough at most cars with bonded panels (roof being the easiest to spot) you will probably find where the adhesive has creased the sheet metal. Thanks! So, how do I keep this from happening on my own piece? This will be my first carbon project, and my first two-piece mold. I've watched all of the (amazing!) Easy Composites videos and I've made a few fiberglass parts, but they were all pretty much lofted 2D shapes that didn't require any sort of reinforcement. This piece is about 42" x 30". I don't expect it to be show-car quality (gotta start somewhere!) but I'd rather not have this problem. Can I assume that, if the inner and outer parts are bonded with resin rather than some weird adhesive, this won't be an issue? (Hello from the nice part of Texas!)
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Hanaldo	Hanaldo posted 4 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	No, you can't really avoid it (it happens to big car manufacturers, they would stop it if they could) its just a side effect of bonding panels. You need a strong adhesive to bond the panels, but those adhesives shrink. So using one with very low shrink will help, but they all shrink to some extent so it isn't completely avoidable. This looks especially bad though, it shouldn't be so bad. Hard to know why it is this bad without knowing what materials were used and how everything was made. I would hazard a guess at quite thin fibreglass skins in combination with poorer quality materials and someone being very heavy handed on the adhesive gun. Also potentially parts that have gotten hotter than the resins/adhesives maximum service temperature.
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raygun	r raygun posted 4 Years Ago HOT Post Details
r Group: Forum Members Posts: 22, Visits: 126	+x Hanaldo - 11/21/2020 6:24:04 AM No, you can't really avoid it (it happens to big car manufacturers, they would stop it if they could) its just a side effect of bonding panels. You need a strong adhesive to bond the panels, but those adhesives shrink. So using one with very low shrink will help, but they all shrink to some extent so it isn't completely avoidable. This looks especially bad though, it shouldn't be so bad. Hard to know why it is this bad without knowing what materials were used and how everything was made. I would hazard a guess at quite thin fibreglass skins in combination with poorer quality materials and someone being very heavy handed on the adhesive gun. Also potentially parts that have gotten hotter than the resins/adhesives maximum service temperature. Well, that's disappointing. But, there's no getting around physics & chemistry. Maybe I should just rivet inner and outer panels together.
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Hanaldo	Hanaldo posted 4 Years Ago HOT Post Details
Group: Forum Members Posts: 2.5K, Visits: 28K	+x raygun - 11/22/2020 1:55:23 PM +x Hanaldo - 11/21/2020 6:24:04 AM No, you can't really avoid it (it happens to big car manufacturers, they would stop it if they could) its just a side effect of bonding panels. You need a strong adhesive to bond the panels, but those adhesives shrink. So using one with very low shrink will help, but they all shrink to some extent so it isn't completely avoidable. This looks especially bad though, it shouldn't be so bad. Hard to know why it is this bad without knowing what materials were used and how everything was made. I would hazard a guess at quite thin fibreglass skins in combination with poorer quality materials and someone being very heavy handed on the adhesive gun. Also potentially parts that have gotten hotter than the resins/adhesives maximum service temperature. Well, that's disappointing. But, there's no getting around physics & chemistry. Maybe I should just rivet inner and outer panels together. Haha yeh that would look worse 🤣 I feel I've made you more worried about it than you need to be. It is not really possible to avoid it altogether - it is possible to avoid it happening to this extent. It should not be so noticeable, generally it is one of those things that you only see if you are looking for it and you catch the reflection at the right angle.
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