dbartromvette

Hey guys I'm new here, I know this question may have been asked in the past but does epoxy primer do the same as what gel coat would do?

I am actually asking this question for my neighbor that is working on a 70 vette.


I am just trying to help him out he doesn't use the internet much!

Alan 71

Hi db,
Your friend's 70 had no gel coat on it originally. It was just fiberglass and resin.
Unless the body has been sanded or blasted so that there is exposed glass fiber I see no reason for it now.
So the epoxy primer would be the first layer of paint.
Regards,
Alan

CHarper

Hi Alan, you are kind of my Vette expert. Along the lines of the original question, I'm prepping my 82 for paint and have areas where I went thru to the glass and areas where the black gel coat is still there. I have researched the forums and net but don't have a clear path to take. Should I use high solids epoxy primer or gelcoat it again. The painter I was going to use has medical issues and is not available anymore and I have not found anyone intrust with this thing yet. I would like to shoot the primer so I can detail the body and let a real painter do the finish on it. Thanks in advance.
Charles

oldgto

So what`s a good filler for chips & gouges that do NOT go all the way down to the fibers? Would "Bondo-Glass" work for those?

blade072

Original fiberglass parts on a Corvette are made from the matched metal molded process. This goes back to the very early Corvettes.
Some of the earlier parts were made from the preform process. The later model parts were made from SMC which is sheet molding compound. The current molded parts are also SMC but might have high pressure in mold coating which is nothing more than a primer. During the molding process, and after the part is almost cured in a matched metal mold, the inmold coating is injected under very high pressure and cured. The temperatures of the steel molds during molding is around 310 degrees F.
I have designed many molds for Corvette parts and had worked for a Fiberglass Molder which was very instumental in getting General Motors to make a Fiber Glass Car.
During my recent years of owning a large machine shop, we built many matched metal molds for molders who molded parts for Corvette.
Your term of Gelcoat is a product used when hand layed up parts are made. These are usually after market parts.
Thanks, Jim

CHarper

Jim it sounds like you know more than most. Am I correct in thinking you advise using an epoxy primer on my 82?

LemansBlue68

I tried the spray gel coat that is available through one of the major Corvette parts suppliers because I heard at the time that it was the only way to "lock" the fiberglass fibers from heavy sanding in place. I tested it on my hood and it came out a mess! The gel coat blobbed on rather than sprayed and it didn't flow out at all. The final result looked like a gray orange peel. In disgust I sanded it all off. That was no party either. It was very hard stuff when cured.

After doing most of the body repairs on the rest of my car, which amounted mostly to filling low spots, I went to a Dupont epoxy primer sealer on the recommendations of an auto paint dealer near where I work. Then I used copious amounts of Slick Sand which is a spray on primer surfacer. My paint guy actually I recommended I use Slick Sand because it was much less expensive than the Dupont equivalent and in his words, "most of it will end up on the floor of the garage as dust anyway". Then after block sanding everything I sealed it again with the Dupont epoxy sealer prior to painting.

It's been 7 years since I painted the car and there is absolutely no signs of the glass fibers showing through as I was first scared into believing would happen if I didn't use gel coat.

As Alan71 said, the original GM fiberglass was not gel coated either. The surface the factory got after the parts were formed by the press molding process is what they worked with prior to painting. They simply primed over that before painting.

markids77

General consensus seems to be that no factory Corvette body panels were gelcoated. Many aftermarket parts were, especially if hand laid, but aftermarket press molded parts largely ended the practice. For anyone looking for a specific epoxy primer recommendation I would Google Southern Polyurethanes, call Barry over there and order up however much of his epoxy primer as you might need. His products seem to hae a large and vocal following here, and that's as fine a recommendation as I can think of.

Steve2147

You don't need or want epoxy. Epoxy is a primer that is used where adhesion challenges exist, paint to bare metal being the most common. It acts like contact cement and is used in place of etch primers that bonded to the metal by way of the acid interaction with the metal.

With epoxy you mix the two parts, spray it on and allow the solvents to flash off. Within the epoxy's recoat window you apply your next layer, usually a high build primer in the form of urethane or polyester. If you let the epoxy sit too long and get outside it's recoat window you have to start the process over. Just like contact cement. You let the cement dry on the two surfaces but before it cures you stick the two parts together. If you wait too long they won't stick.

No such adhesion challenges exist with fibreglass. With the properly abraded surface you go directly to a high build primer. Polyester is the recommended high build for use on fibreglass.

You can use epoxy, but it is not necessary, needs to be recoated during it's recoat window, sands poorly if you miss the recoat window and adds to film thickness.

Steve g

dbartromvette

Sorry, I should have been a little more clear when I posted the original posting. He has soda blasted the entire body. He is doing a frame off restoration. He has the frame just about completed, and it looks amazing! The car is going to be a numbers matching better than original 454 4spd car.

He is a vette lover and has 4 C3's! He just doesn't know how to work the internet too well. Thank you for all of your help, he will be amazed when I show him all the responses. Hopefully enough so that he joins and starts to share here on the forum!

Easy Mike

There is no gelcoat. I think the "black" you see is actually dark gray factory printer. I found it on my 80.

markids77

Fiberglass is porous and will absorb most anything it comes in contact with. After 30 plus years of exposure to road tar, tire shine, oil leaks, etcetera I posit that any fiberglass body is likely "adhesion challenged". If you want to risk wasting your $1100 or so topcoat paint, plus the labor to strip and redo your job because you think epoxy isn't worth the effort go right ahead. It is inexpensive insurance against a forseeable difficulty; not an absolute guarantee of good result, but better than ignoring the possibility.

Steve2147

How did the road tire, grime etc penetrate the finish that has been removed and compromise the figreglass below it? If you have any of those contaminants on the surface you're painting you shouldn't be putting epoxy over it either.

The characteristics of the bare fibreglass surface are not much different than those of a cured urethane or polyester high build. And we don't apply epoxy under additional coats of those when cured and properly abraded. All my reading and experience suggests that the quality of bond between the bare fibreglass and the polyester or urethane primer resins are as good, if not better than the epoxy bond.

I'm a strong believer in the use of epoxy. I use it on even the small bracketry when doing restoration work. But I don't use it when all it's giving me is additional film build.


Each to his own, but to keep the risks and fears in perspective, the paint manufacturers don't seem to feel you are risking your $1100 or so of topcoat paint (per the tech sheets), and they warranty it.

Steve g

blueray72

body and paint forum

csherman

I use Slick Sand - other like Feather Fill
two part - does a very good job on bare fiberglass

markids77

I believe the correct terminology is "wicking". The contamination soaks in from the underside of the panel and may not be obvious in its presence (ie blistering/cracking of paint film). A couple extra mils of paint film and a bit of extra expense gives me peace of mind, your mileage may vary.

Manuel Azevedo

No original corvette body parts ever had Gel-coating! FRP and SMC bodies are like a sponge and porous, thats why you want to seal them after years of contamination and for a good base/foundation to do your body work/painting on, you should even consider the bottom side of the glass also at lease the ones you can get too. The use of a gel-coat or an epoxy is highly recommended with the real difference between the two just personal preference. Have seen great results with both. Epoxy is probably a bit less labor intensive and SPI epoxy would be the best to use IMOP!
And no I'm no great painter at all but my projects have come out well and the best looking jobs I have seen have been with SPI products/epoxy. No I'm not connected with them either!

CHarper

Thanks for the advice on Barry. I spoke with him this morning and he is the expert I've been looking for. He walked me thru what needs to be done and sold me the products I need.

69Vett

Recommend the SPI products, great products,
and ... great personal service. talk to Barry

Steve2147

If you've got contaminants wicked through your fibreglass from the back side the type of primer you use is the least of your problems. And a layer of epoxy is not going to save a panel that will be something akin to wet paper towel. As well, the areas of finished surface where the back side of the panel is actually exposed to the elements are relatively few and very small. And almost all of those were coated with a rubberized undercoat from the factory.

As I said, if it gives you peace of mind, great. My point was only to say that one shouldn't feel their $1,100 of topcoat is at risk when they are following procedures and using the materials recommended by the paint manufacturers. For me, and others that follow the recommended procedures, all we would get is extra expense and film build.

Steve g