Corvette with SMC

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Hello. Noob here. This has probably been beaten to death, but I couldn't find anything definitive. I have a 1995 Corvette with several coats of paint in some areas that I DA'd off with 180. So, it's gonna need a lot of blocking. I have sanded into the SMC in some areas. A couple spots need some fiberglass filler before proceeding. I bought 2K Primer because the description states it adheres to fiberglass. I was going to continue sanding 220, 320 and apply the primer. Should I be putting epoxy primer down before the 2K due to the SMC showing and there will be a few small repairs also. Thanks.
 
Epoxy is the best thing to stabilize bare fibers, imo. Obviously it's more critical on an older 'Vette, but if I was doing it I would start with epoxy for sure, just to be safe. Maybe not on a quickie SMC repair, but if it's gotta be nice and last a long time, epoxy for sure.
 
Epoxy only on bare fiberglass/SMC. Also being your Vette is SMC only use SMC type fillers.

UPOL makes a good SMC filler.

 
Epoxy is the best thing to stabilize bare fibers, imo. Obviously it's more critical on an older 'Vette, but if I was doing it I would start with epoxy for sure, just to be safe. Maybe not on a quickie SMC repair, but if it's gotta be nice and last a long time, epoxy for sure.
Thanks for the technical resource link. It states to use epoxy primer on bare SMC before applying any fillers or 2K primers. I'm assuming it is referring to polyester fillers as I am planning on repairing the bare SMC in spots

Edit: When I say repair I mean there are some cracks and I have to build up a small piece that got broke off
 
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Never apply any filler over bare smc/fiberglass....only over epoxy for long term results
Wouldn't I fix the cracks prior to putting on any product? I gotta V it out an put the SMC filler in. According to the above statement, this would be incorrect.
 
When I've had to V something to fix a crack using a product like I posted above I'll use it directly on the SMC. Never seen any issue doing that.

I've done SMC and fiberglass repair the same way as outlined by SEM here:

Conventional Filler or glaze I will always apply over epoxy, rather than directly on SMC or 'Glass.
 
When I've had to V something to fix a crack using a product like I posted above I'll use it directly on the SMC. Never seen any issue doing that.

I've done SMC and fiberglass repair the same way as outlined by SEM here:

Conventional Filler or glaze I will always apply over epoxy, rather than directly on SMC or 'Glass.
Thanks for clarifying that. That's how I have done fiberglass repairs in the past. My repairs are very minor. The imperfections are very small nothing at all like the above video or what you see on other YouTube videos. Do I have to let the Upol dry for hours or days to outgas before I put epoxy primer on the panel? Another thing I've read is not to use any kind of solvent on bare SMC, only soap and water. The SMC will soak up the solvent and not release it. What are your thoughts on that?
 
Anyone ever use this? A few of the self proclaimed best over on Instagram talk about using this stuff on old corvettes.

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Sounds like repurposed and renamed gelcoat, or at minimum based upon it. It would be interesting to learn why they think this is so much superior to, for instance, a normal poly primer.
 
This has come up before. Here’s what Jim had to say:

yeah duratec make alot of polyester primers and other products for the fiberglass and composites industry. they make very good stuff. i had about a dozen gallons given to me some years back. the problem with it is, its really hard and sands like a rock. when i say its hard i mean really hard. nothing like what we are used to in the autobody world. you will be block sanding until your arms fall off lol. i used it on one automotive project and i swore never again. i ended up using the stuff to coat the plywood tops on my work tables in the shop. unless its something you can use a da on then dont use it.
 
Sounds like repurposed and renamed gelcoat, or at minimum based upon it. It would be interesting to learn why they think this is so much superior to, for instance, a normal poly primer.
Some of them have said with the expansion and contraction rate of fiberglass.
 
This has come up before. Here’s what Jim had to say:
yeah duratec make alot of polyester primers and other products for the fiberglass and composites industry. they make very good stuff. i had about a dozen gallons given to me some years back. the problem with it is, its really hard and sands like a rock. when i say its hard i mean really hard. nothing like what we are used to in the autobody world. you will be block sanding until your arms fall off lol. i used it on one automotive project and i swore never again. i ended up using the stuff to coat the plywood tops on my work tables in the shop. unless its something you can use a da on then dont use it.


damn you really had to go back in the archives to dig that one up...lmao!

just a little info on smc. the reason smc needs specialized stuff to adhere to it is because that stuff comes in a big sheet and the mold release is actually built into the resin and fibers. when you grind into it to do a repair its far more difficult to get things to bond to it. any structural repair to smc cant be done with regular polyester resins because it wont sick 100% and will pop under stress. smc resins and epoxy resins are ok. your repair can be done with west system and glass for instance. when doing a fiberglass repair you go direct to the glass just like any other repair. if you just need a little body filler though then you would need to put epoxy primer down as a barrier before hand, which i believe is what barry was trying to say. for a filler though, if you just use adtech p17 filler then you dont need to worry about any of that since that is a body filler that sticks to smc and about everything else.
 
for a filler though, if you just use adtech p17 filler then you dont need to worry about any of that since that is a body filler that sticks to smc and about everything else.
Thanks Jim. I ordered the UPOL filler the other day . I could have saved $30 getting the Adtech P17. The repair process is the same, being a direct to SMC correct?
 
@Jim C That is great info Jim......pure gold. Thanks for sharing that. I always knew that you should only use SMC products on SMC but I didn't know the exact reasons why....now I do.:)
 
Wow Jim, your website is impressive. That is some phenomenal work.
Sorry for all the rookie questions folks, but I think others can benefit as well.
I have some pictures of what I am working with. Crack 1. is on the quarter panel and is from an accident, it's about an inch long, Crack 2 is on the hood about 1 inch in diameter and is hail damage. Crack 3 is from the same accident as Crack 1, I need to build a little bit like an 1/8 or 1/16 on the lower trailing edge. Should I be using epoxy resin before the filler on 1 and 2 or will the SMC filler work since it is a bonding agent? Should I block the car with a certain grit before epoxy primer? Thanks
 

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Listen to Jimc, I've done vettes all my life and only fixed a few, with the newer ones being c3 through c6 for friends.
But I have logged 1000s of hours since full SMC came out in 84 trying to save panels for shops where the poor painter listened to a paint rep that said some as fiberglass.
Some panels we could not save.

A few notes as some items here make me not want to respond, so I will throw out a few suggestions and take them as you wish.

1. Do not clean the glass with wax and grease remover or acetone, as some reps will say.

2. On raw SMC, the only thing I will use is vette panel adhesive or a two-part cartage system with a gun.
I saw one of the items listed that three weeks after the shop made the door repair pull off like a band-aid about a 2-foot section.
When I told the shop how to fix they said they would eat a new panel.
 
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