I am in the process of removing the paint off of my 1976 Vette. I have restored and painted a few cars over the years but this is my first Corvette. It appears I have a few things to learn about SMC panels. I have been advised to spray 2 coats of epoxy primer onto bare SMC panels when done stripping. Problem is I live in the Northeast and it will be to cold to spray epoxy during the winter months. So I'm thinking I can do my body work during the winter and spot heat areas I'm working on. So my questions are

1) Best SMC resin and body filler to use?
2) Does it matter if I apply resin and matte directly to SMC panels?
3) Can I add fillers, sand directly to SMC panels
4) I will be adding fiberglass chrome bumper mod and filling seam. Can I use SMC filler for that? Worried I will see seam after painting
5) Body has minor crack in it. Thinking grind out crack and just fill Thoughts?
6) I read some place that solvents for cleaning SMC panels is very bad. Even water is bad Any truth to that?

 

1) Best SMC resin and body filler to use?

Just find a US manufacturer of the product.

2) Does it matter if I apply resin and matte directly to SMC panels?

You need to have a clean, grease and silicone-free, surface that is sanded with 80 grit.

3) Can I add fillers, sand directly to SMC panels

Same answer as #2.

4) I will be adding fiberglass chrome bumper mod and filling seam. Can I use SMC filler for that? Worried I will see seam after painting

Do all your modifications with mat/resin. Only use fillers for the final surface prep.

5) Body has minor crack in it. Thinking grind out crack and just fill Thoughts?

Taper grind ~ 1 1/2 inches on either side to a feather edge at the crack. Best if you can replicate on the backside.

6) I read some place that solvents for cleaning SMC panels is very bad. Even water is bad Any truth to that?

Quality of cleaners is critical. I use Klean Strip Prep-All. High grade lacquer thinner is good as well.

 

Hi JamminG,
I would suggest you picked a reputable manufacturer and contact them about your project. I used Evercoat products since they are easy to get in the Mid-Atlantic states and their tech sheets were detailed so even a novice like me could choose the products that work best with fiberglass/SMC. Chemistry matters and after reading tons of posts on this site, many written by a very experienced member who went by the name of DUB (RIP), I realized fiberglass can act like a sponge so keeping that bare fiberglass clean and protected is critical. The speed you will be working at should also dictate your process. I stripped my 71 with a chemical stripper during the summer months and after it was down to bare glass I washed it, or should I say I flooded it with water and Dawn dish detergent to make sure all traces of the stripper were removed. Since I planned on putting it out in the hot sunshine for days on end and the fact that it would sit all winter long before I painted it, I did not worry at all about any residual water being trapped in the fiberglass.
Good Luck,
Mr. K.

 

Most body filler is polyester and polyester won't stick to SMC. You might think it's bonded well, but I remember some fiberglass repair I did to a hood...waaaaay back years ago when I was young. It looked great. But somehow I got picking at it, and the whole entire patch/repair 10" long x 2" wide flicked off in one piece like an old dry scab!! Effortlessly. That was eye opening.

So #1, DO your SMC repairs first. The we'll get to the priming and bodywork in a moment. For the SMC repair, use EPOXY resin (not Polyester)....and fiberglass mat and cloth as needed. Generally, if you have a crack, say, an 8" crack, you drill an 1/8" or 3/16" hole at the end of the crack so it doesn't 'creep' over time. V-out the crack with a grinder. A rough edge is great and will give the epoxy and fiberglass plenty to grab onto. Blow out the ground-out v-shaped valley good ad clean. Cut various widths of fiberglass cloth narrow (to fit into the bottom) and wider to fan out as it's built up. Cut plenty of strips because you want to pack the new strips in tight for a strong repair. So...like 6 strips to lay on top of each other is a good start. Once you get the strips cut and laid out organized. Then mix up the epoxy. What you can do for epoxy is assess how much you'll need. If it's only a handful of repairs, my suggestion is to go to the home center and buy a couple 2-3 dual-syringes of clear epoxy. Just the normal stuff. Nothing fancy. Not for boats, not for refrigerators...not for aircraft, not "like steel" ... just normal ole inexpensive clear epoxy. Mix up some in a small cup..mix up plenty. Put some on the v-out area and apply the strips of fiberglass. Then put more and more layers on top. If you need more epoxy, spoon some more on. The more strips and the more you pack it in 'tight' the stronger the repair. Ideally you would roll them in with a fiberglass roller like

THIS

THIS

. That's a nice tool to have. If you have one repair, it's probably not worth to buy it. But if you have multiple repairs, it makes for a cleaner, neater and less messy job. Put enough on that the repair is taller than the surrounding SMC. Then grind it off the next day once it's fully cured. Wear an N95 mask.

Ok...you have your fiberglass repairs done and ground down nice. Now it's time to apply an Epoxy primer. I would epoxy the whole car. You must have one day that's above 50*F if you're going to spray outside....don't you? Spray on a couple coats and roll it back in the garage. Not all primers are suitable for SMC, to quadruple-check your product's spec sheets. Get something that has some 'build' to it. If it doesn't have any 'build' then apply a 2k high-build over the epoxy ..while it's wet ..by 'wet' I mean wait a while for the reducers to flash off (a hour??) then apply your 2k as needed. Roll the car back into the garage and leave some heat on..let it cure-out. You should post a pic of your car's repair areas so we can see what you're up against. I might apply a guide-coat over the entire car while it's still a bit soft, but that's optional. Give the primer a week to cure and possibly shrink. Then sand the repaired/bodywork areas with 80# sandpaper. Blow off real well and apply your body filler over that. I really like the 3M Platinum Plus. Great product HERE. I (and many guys) do the same prime-process over steel cars...and do bodywork over the primer. You get better adhesion and better corrosion-reisistence. Try not to sand through the primer as little as possible. When you're finished with your repair re-prime over the filler, apply a guide-coat ....let cure, and fine-tune as needed.

Yes, they do make fillers you can do over different substrates, but I've read of guys having "suitable' filler later flake off. I wouldn't chance it. Do the repair over the primer and you'll never have to 'guess' if it's going to hold.

Does that answer your question?

 

You can use solvent (lacquer thinner or acetone) on the SMC but NEVER use Wax & Grease Remover (over bare smc). What will happen is the fiberglass strands will 'wick' it into the material and you can't get it out. And it'll screw up the primer/paint. Once you get the car covered in primer, you can use W&G/R. Not before.

I think if you V-out a repair 3/4" or 1" on both sides of a crack that's plenty.