Corvette with SMC

Looking at those pictures, if i was fixing those i would take a 2” grinder with a 36grit disc and dish out those cracks until they were completely gone or you were close to going through. I would mix up some west system and glass, lay up enough layers to build it up higher than the surrounding area. Let cure 24hrs. Come back and grind it flat then skin it with adtech, block smooth, epoxy primer then on with the rest of your paint process. I have heard may guys mention the vpa adhesive but i have never personally used it so i cant comment on that. Personally i always repair glass with glass.
 
Resins that say they are for SMC have always worked fine for me. They use the same cream hardener as plastic filler. In fact, I only keep that around and use it on conventional fiberglass as well. It works fine on both.
 
I've repaired some header panels that were smc with the west system resin. It's obviously more money, but I like the results.. Also on cracks like that I typically drill a small hole at the end of the cracks to stop them. I've had cracks come back and those problems went away when I started doing that.

I would have never thought to epoxy the smc before any filler, but I will adopt that process. or move onto that filler Jim C recommended.
 
Jim C said:
Looking at those pictures, if i was fixing those i would take a 2” grinder with a 36grit disc and dish out those cracks until they were completely gone or you were close to going through. I would mix up some west system and glass, lay up enough layers to build it up higher than the surrounding area. Let cure 24hrs. Come back and grind it flat then skin it with adtech, block smooth, epoxy primer then on with the rest of your paint process. I have heard may guys mention the vpa adhesive but i have never personally used it so i cant comment on that. Personally i always repair glass with glass.
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That's what I'll do. I'm going to order the Adtech and West Systems straight away. It's not that money is no object, but whatever it costs for least likelihood of failure is the way I'll go. I have been wet sanding my car because the paper last much longer. Will that have adverse effects on the bare SMC? Like will it retain water? It sits out in the elements. Thanks
 
I cant recommend the adtech enough. Its not like any other typical body filler. Its like a solid plastic when cured. Its structural and has strength to it almost like the way solid polyester resin is when it kicks off in a cup. It doesnt sand super easy like some bodyfillers because of that but its not terrible. it doesnt shrink, crack or swell. I believe its rated to 450deg also. In the marine world they dont use bodyfiller like we do. They use adtech.
 
i have used VPA for a long time. it sands just a little harder than other fillers but that is a plus for me . i dont like easy sanding filler or primers . VPA has excellent adhesion . just have to learn to apply it cleanly to reduce sanding . i use a 6in broad knife on filler and if skimming a big area i keep my 12in mud knife handy to finish . every one of those spreader lines will give you fits trying to level a panel . plastic spreaders leave waves .
 
@Jim C Is this the correct filler even though it says "Polyester Filler System"? Thanks
 

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Chris_Hamilton said:
When I've had to V something to fix a crack using a product as I posted above, I'll use it directly on the SMC and never seen any issue doing that.

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

How To Complete an SMC Repair | SEM PRODUCTS

Reduce steps and save money on your next SMC repair with SEM’s new 2-in-1 Fleet Line™ Composite Adhesive & Repair.
www.semproducts.com www.semproducts.com

Conventional Filler or glaze I will always apply over epoxy, rather than directly on SMC or 'Glass.
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This is correct, and as I explain to people, the major V-grove areas fix first, and the minor imperfections glaze or filler over epoxy.
SMC, you must be very careful what you put over it.
 
I don't know what grit to sand my car with or what to wipe it down with pre-SPI epoxy. The document states 80-grit on steel, I don't know if that applies to SMC. I've been searching since I started this thread and haven't found a definitive answer. Everybody does it different. The whole top half of the car has at least 2 paint jobs on it, factory and 1 more hail repair done at a body shop.The hood and 1 quarter had more paint. I DA'd the hood and rear of my car with 180 and I'm repairing the bad spots now. I'm taking the doors apart to sand them. The top of the doors doesn't have all the build up like the hood, The sun has beat it down. The bottom half of the car is factory and sands easily. I sanded the gill panels with 320 and was pleasantly surprised. The doors won't be bad and need no repairs. I'm thinking I can sand the doors once and they will be ready for epoxy as long as I use the proper grit. I was going to sand the urethane bumper covers with 320 like I did the gill panels. My plan is to block it before epoxy to get it halfway flat. I'm unsure what to block it or clean it with for the best likelihood of long term success. Another thing. I am planning on applying SPI urethane primer over the epoxy without sanding. Please advise. Sorry for the long post. TIA.
 
My own preference would be to epoxy anything that is not metal with 150 or finer. Typically on a job like that we will use many grits, starting with 80 (Maybe even 40 if there's lots of paint) and working up to perhaps 220. Lots of people primer over coarse scratches, I don't.
 
crashtech said:
My own preference would be to epoxy anything that is not metal with 150 or finer. Typically on a job like that we will use many grits, starting with 80 (Maybe even 40 if there's lots of paint) and working up to perhaps 220. Lots of people primer over coarse scratches, I don't.
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Thanks. Will the epoxy primer bite on 220 or even 320? I'd like to start the foundation at the best possible level.
 
It's my opinion, based on experience, that epoxy sticks really well no matter the grit, as long as the sandpaper was sharp and the surface is clean. Metal gets a coarser grit mostly because solvents don't penetrate it and help the epoxy wick into the surface as what happens when priming SMC or other materials that aren't 100% solvent resistant like metals. But it would be interesting to hear from some others on this subject.

The reason I tend to use a finer grit on non-metals is partly because solvent will penetrate those substrates and can evaporate very slowly over time. Priming over coarse grits combined with unexpected shrinkage that comes from this solvent evaporation is a recipe for failure, because the mapping of coarser grits is more visible and less likely to be easily repairable.
 
I agree on the grit. While 320 will work its prob a little on the fine side as prep for your foundation. 80 is good fir steel but softer stuff like aluminum and plastics i will do 180. Occasionally 220 but 180 is pretty much my go to grit for something like bare glass/smc
 
180 is a great compromise. For whatever reason in my shop we skip that grit and have either 150 or 220 on hand, and I like the results from 220, or at least 150 that has been "kissed" with 220 and a red scuff pad. Part of why finishing with a fine grit is a thing with me is that I worked my way up in collision shops that would prime over all kinds of bad prep work. Sometimes if the delivery of the vehicle was delayed for a few days, it was too easy to see the dulling of the finish over the repair areas, and never mind if a vehicle came back, because the shrinkage over the repair areas was awful. All the mapping of the repair was clearly visible, because it hadn't finished in finer paper. This was in various high-end SoCal repair facilities on mostly late model vehicles. In my opinion, most collision/body repairs are done in a crappy fashion if the conventional advice is followed, and I would rather nip that in the bud if possible.
 
Thanks for all the help so far. My hood, rear bumper and gill panels will be ready for primer tomorrow. I had to patch some spots in the hood and there is some bare SMC. It's pretty flat with the hand test. The bumper and gill panels I sanded through the paint in some spots, I didn't do any work on them. The bumper is urethane and the gill panels feel like plastic. I was going to shoot epoxy on all the parts and follow it with a coat of standard 2k primer on the bumper and gill panels, and 2? or 3? coats on the hood. Please advise. TIA
 
I sprayed 2 coats of epoxy on the hood today. There's a bunch of waves in it from the DA and some pinholes in the P-17 and some knicks from the razor blade (so much for the hand test). For tomorrow, do I put the glaze in the spots that need it and knock it down, then (without sanding the rest of the hood) put primer on Wednesday? It's within the window, I just want to make sure since I'm sanding part of hood should I sand the whole thing? Thanks

Edit: Also you can see the spots where the SMC ends and paint starts, where it's feathered.
 
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You can apply glaze on fresh epoxy without sanding. Then the glaze would be sanded down to level with the body prior to repriming. Typically I will block sand any areas to be reprimed, because I never want to miss a chance to make the body straighter by removing material that doesn't belong and leaving material that does. But, as long as the epoxy is in the 7 day window, you can re-apply more whether the surface is sanded or not.
 
Edit: Also you can see the spots where the SMC ends and paint starts, where it's feathered.
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Why did you not strip? This could be a problem down the road on a vette, it not like doing a metal body, just saying.
 
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