I have a 75, definately SMC.
Any SMC in C3s?
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Any SMC in C3s?
Hi all, i am doing repair work on a 68 vette here in australia. I am grafting in a second-hand firewall section that is from a 1975 C3. The reason for this question is a very noticable color difference... now, it could be a few years of sun bleaching making the donor section whiter, but..... I know C4s were SMC and have heard rumours of SMC being used in some C3s... I need to make sure as it would effect how this repair is done. I have also been told that a change of resin occured in C3s and that could be the color difference (both still types of polyester resin though)
Any answers?....
Any answers?....
Pro
Joined: Sep 2006
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From: Carlstadt NJ
Hi all, i am doing repair work on a 68 vette here in australia. I am grafting in a second-hand firewall section that is from a 1975 C3. The reason for this question is a very noticable color difference... now, it could be a few years of sun bleaching making the donor section whiter, but..... I know C4s were SMC and have heard rumours of SMC being used in some C3s... I need to make sure as it would effect how this repair is done. I have also been told that a change of resin occured in C3s and that could be the color difference (both still types of polyester resin though)
Any answers?....
Any answers?....
Danny
Team Owner
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From: Southbound
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thanks all for the help
Thread Starter
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ok, thanks... More questions now, i have played with smc on c5s and know it is very white and marble looking. I have repaired some 71s and 72s and have found the panels to be grey all over with no color or texture differences between what you say would be say, an smc fender and the rest of the body. So, were they still using polyester resin in the new smc? With the white late model smc i know that a different resin is needed to do repairs.
Thanks all for the help
Thanks all for the help
Melting Slicks
Joined: Nov 2004
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From: Nevada City California
I haven't seen any '71 models with SMC fiberglass, unless the body has been repaired since new. I owned a pretty late car, built July 13 and it had polyester fiberglass.
I have seen '72's with rear quarters in sheet molded composite fiberglass.
I have seen '72's with rear quarters in sheet molded composite fiberglass.
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Again, C4 and C5 panels are super easy to spot as smc i know, but i have not yet seen that sort of 'smc' panel on up to 72...
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From: Fremont CA
I have always been told the 2 systems aren't very compatible with one another. Bonding agents for the 2 types of glass were different, but, I'm not the expert on body panels, I pay someone to itch for me
Corvette Image in Oregon makes ployesther panels like facotry stuff for the older Vettes. You may want to give them a call. Link: http://corvetteimage.com/
Corvette Image in Oregon makes ployesther panels like facotry stuff for the older Vettes. You may want to give them a call. Link: http://corvetteimage.com/
Race Director
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From: Plano TX
The C3 SMC is NOT the same as 84-up SMC. The C3 panels, both SMC and non-SMC had different colors depending on the supplier. I have personally seen grey, white and black.
All C3 panels can be bonded with either polyester or epoxy resin. 84-up SMC can NOT be bonded with polyester resin.
You can tell the C3 SMC panels by the marbled look. Fiberglass was a uniform color.
All C3 panels can be bonded with either polyester or epoxy resin. 84-up SMC can NOT be bonded with polyester resin.
You can tell the C3 SMC panels by the marbled look. Fiberglass was a uniform color.
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Melting Slicks
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From: Nevada City California
Every '72 Corvette that has had partial SMC panels the color was off white, but the more noticeable difference, especially the rear fenders is the thickness of the panel. Easily distinguished from the original black polyester panels.
Race Director
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From: Florida
SMC was first used in some parts on the later C2s and it's use increased every year since.
The colors varied and the resins were always a polyester based, but the length of strands and ratio of fiber to resin changed and improved almost every year in the 70's and 80's. It's an ever evolving chemistry.
The SMC info is useless. Use nothing but epoxy for all repairs.
It is the only resin that can grip polyester, vinylester, epoxy composites or any combination thereof, or any type of SMC without failure, if prepped properly.
I have a wheel apron here that someone used polyester to repair and it has failed. Should take a pic of it sometime.
The colors varied and the resins were always a polyester based, but the length of strands and ratio of fiber to resin changed and improved almost every year in the 70's and 80's. It's an ever evolving chemistry.
The SMC info is useless. Use nothing but epoxy for all repairs.
It is the only resin that can grip polyester, vinylester, epoxy composites or any combination thereof, or any type of SMC without failure, if prepped properly.
I have a wheel apron here that someone used polyester to repair and it has failed. Should take a pic of it sometime.
Melting Slicks
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From: Massapequa Park NY
Jim
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thankyou everybody, as usual, always helpful.
shoot me if i am wrong but here goes how i understand this issue now...
Polyester based resins were used from the start right through to the end of the C3 series. During that time particularly in the early 70s progressive changes were made to the manufacturing technique. these changes have become termed 'smc' or sheet moulded compound in order to differentiate from the earlier panels seen in the C2 and early C3, (grey) In reality though, right from the early days, could not panels be termed 'sheet moulded compound', that is, fibreglass sandwiched between two sides of a mould, producing smooth finishes on both sides of the panel? What differed over the years was the actual manufacturing process more than a drastic change as we see with the C4 on panels.
I reason this way to separate C3 'smc' from C4 smc which we all know is a very different resin base and fibre, requiring of course a different repair method.
what say you guys?!!!
shoot me if i am wrong but here goes how i understand this issue now...
Polyester based resins were used from the start right through to the end of the C3 series. During that time particularly in the early 70s progressive changes were made to the manufacturing technique. these changes have become termed 'smc' or sheet moulded compound in order to differentiate from the earlier panels seen in the C2 and early C3, (grey) In reality though, right from the early days, could not panels be termed 'sheet moulded compound', that is, fibreglass sandwiched between two sides of a mould, producing smooth finishes on both sides of the panel? What differed over the years was the actual manufacturing process more than a drastic change as we see with the C4 on panels.
I reason this way to separate C3 'smc' from C4 smc which we all know is a very different resin base and fibre, requiring of course a different repair method.
what say you guys?!!!
Race Director
Joined: Mar 2006
Posts: 14,112
Likes: 28
From: Florida
thankyou everybody, as usual, always helpful.
shoot me if i am wrong but here goes how i understand this issue now...
Polyester based resins were used from the start right through to the end of the C3 series. During that time particularly in the early 70s progressive changes were made to the manufacturing technique. these changes have become termed 'smc' or sheet moulded compound in order to differentiate from the earlier panels seen in the C2 and early C3, (grey) In reality though, right from the early days, could not panels be termed 'sheet moulded compound', that is, fibreglass sandwiched between two sides of a mould, producing smooth finishes on both sides of the panel?
From day 1 the panels were smooth on both sides (compared to hand or chopper gun layup) and the process of using a mold resulted in "press molded panels", not smc. Smc panels among other things had the release agent added.
What differed over the years was the actual manufacturing process more than a drastic change as we see with the C4 on panels.
There were countless changes at the chemistry level, but the biggest was to add a release agent to the mixture itself to speed production. There was also a change in the resin/fiber ratio for weight, strength and cost considerations. Less resin more fiber.
I reason this way to separate C3 'smc' from C4 smc which we all know is a very different resin base and fibre, requiring of course a different repair method.
Where did you come up with that???
The repair methods are the same.
what say you guys?!!!
shoot me if i am wrong but here goes how i understand this issue now...
Polyester based resins were used from the start right through to the end of the C3 series. During that time particularly in the early 70s progressive changes were made to the manufacturing technique. these changes have become termed 'smc' or sheet moulded compound in order to differentiate from the earlier panels seen in the C2 and early C3, (grey) In reality though, right from the early days, could not panels be termed 'sheet moulded compound', that is, fibreglass sandwiched between two sides of a mould, producing smooth finishes on both sides of the panel?
From day 1 the panels were smooth on both sides (compared to hand or chopper gun layup) and the process of using a mold resulted in "press molded panels", not smc. Smc panels among other things had the release agent added.
What differed over the years was the actual manufacturing process more than a drastic change as we see with the C4 on panels.
There were countless changes at the chemistry level, but the biggest was to add a release agent to the mixture itself to speed production. There was also a change in the resin/fiber ratio for weight, strength and cost considerations. Less resin more fiber.
I reason this way to separate C3 'smc' from C4 smc which we all know is a very different resin base and fibre, requiring of course a different repair method.
Where did you come up with that???
The repair methods are the same.
what say you guys?!!!
Spending an extra 20 bucks is money well spent for epoxy.
Pro
Joined: Sep 2007
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Does epoxy shrink over time?
Melting Slicks
Joined: May 2004
Posts: 2,084
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From: Aussie expat in Saudi Arabia
I spliced 72 egg crate grill fender sections onto the lower half of my 82 using 3M8115. 72 Fiberglass to 82 SMC, no problems. Brilliant stuff 
Last edited by saudivette; Oct 26, 2009 at 09:00 AM.
Race Director
Joined: Mar 2006
Posts: 14,112
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From: Florida
You can mix it thicker to make your own adhesive or body filler. Buy the pumps for an extra 5 bucks to get an exact mixture.
Local in Ft Lauderdale or check their website.
This epoxy has about a 1% shrinkage rate and will not shrink more after full cure. Just add a bit on initial use to sand smooth. Polyester varients have much more shrinkage.
Pro
Joined: Sep 2007
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Here is what I use a lot. Around 50 bucks for approx a gallon.
You can mix it thicker to make your own adhesive or body filler. Buy the pumps for an extra 5 bucks to get an exact mixture.
Local in Ft Lauderdale or check their website.
This epoxy has about a 1% shrinkage rate and will not shrink more after full cure. Just add a bit on initial use to sand smooth. Polyester varients have much more shrinkage.
You can mix it thicker to make your own adhesive or body filler. Buy the pumps for an extra 5 bucks to get an exact mixture.
Local in Ft Lauderdale or check their website.
This epoxy has about a 1% shrinkage rate and will not shrink more after full cure. Just add a bit on initial use to sand smooth. Polyester varients have much more shrinkage.
Thanks for the response.