79vetter

I have read the posts on here that state that Gel Coat is old school and that Epoxy primer is the way to go. I found a painter for the '78 - he says he's been doing Vettes for 30 years. He likes to spray a Gel Coat and then a BC/CC system.

Will Gel Coat work and work well long term or is it a mistake to use nowadays?

zwede

Gel coat is fine as a base to block sand on. If the original panels have been over sanded before, gel coat is good in that it adds strength back to the panel.

You still need to primer the gel coat before BC/CC.

wombvette

Earlier cars, but not on `78. It has SMC panels and gel-coat is not really compatible.

porchdog

gelcoating was big in the 70's to hide bodywork under lacquer paint. most would spider web after a while. i am a believer in epoxy . but if you do gelcoat be careful which resin you use.

Scott Marzahl

Can't gelcoat SMC!! You'll need a new painter that knows WTF he is doing.

porchdog

but i was trying to be nice i did it in the 70's and saw many that just blew up come winter. i use nothing but epoxy now. i stopped using polyester on them also.

0grandmastercorvette

Due to the porous properties of the press molded fiberglass. Not using gelcoat can cause problems with allowing SOME paint problems to "come to life".

Back in the day there was lacquer primer which didn't seal up the fiberglass as well as it needed to do. GM didn't gelcoat Corvettes because for some reason, the blistering, bubbling, crazing, and checking of the body and paint was not an issue for them to consider in a PRODUCTION enviroment. Then came the SMC body panels which stopped these issues...for the most part but...not entirely. SMC still has some problems of its own.

PROFESSIONALLY SPEAKING:
Gelcoat is the way to go. There is no product on the market that compares to gelcoat or has all of its capabilities. Many people use other products that they find work for them and that is their choice...and by me, whatever "trips your trigger" is fine by me becasue I am not going to tell others that they are wrong in their choices and what works for them. But you can not compare any product to gelcoat.

All I am saying is that NOTHING is like gelcoat...PEROID.

When gelcoat is applied correctly and at the proper thickness, it provides a protective covering to your fiberglass that makes it stop many of the issues that press molded fiberglass has going against it far better than other products and this also includes polyester primer which is very, very close to gelcoat but yet not the same. Once again... I am not saying that spraying on something else won't work...but I choose to use gelcoat.

Gelcoat will give your primer or sealer a solid foundation to adhere to without any problems with surface sensitivity and solvent reaction which can occur with other products. Not always ... but problems can occur due to many of these products take a while for them to get to a TOTAL CURE stage. This is evident when a fresh paint job has to be repaired for some reason and when the same products are applied to the sanded layers of the repair area. The solvents can attack these layers and cause a problem with blistering or swelling or shrinkage in the future which creates a "bulls eye" which means that they were not TOTALLY CURED. They were and are still soft in term of hardness and that is where they differ with gelcoat.

I have never run into a "spidering " effect due to the gelcoat. This is usually due the fiberglass being thin (in an area that is under stress when installed ) when the panel was manufactured and the factory let it go out the door anyway. I have seen more of this problem than any, especially around the hood hinge area.

23 years+ of painting Corvettes and I have not had to warranty one paint job due to failed gelcoat.

The choice is yours. You can gather how I feel about this issue. There are other ways than what I have expressed, and if they work.....then they also can not be wrong. Every painter has their way of doing what works for them...just make sure that you find a painter that has your interests on the top of the list. And thet they are going to give you a guarantee for worked performed.
"DUB"

0AmericanCustomInd

79vetter

Can or can't you gel coat SMC?

roger55

I am in the camp of Wombvette, Scott and porchdog.
Gelcoat is polyester and not compatible with SMC.

I would go with Epoxy.

And, the factory never used Gelcoat on any year period.

wombvette

Thanks, Roger

But, to be absolutely 100% correct, some 54s and some parts of pilot line cars were gelcoated. A very few, but some.

porchdog

i've gel-coated a lot of corvettes in my day. lacquer sucked over repaired glass . i've seen some failures over the years i've seen success . i just don't like pushing my luck. i like the adhesion of epoxy and the fact it stays flexible . the only problems i fight is with polyester. the only ghost on the last car were small spots of duraglass. from now on i will do all my fill with epoxy resin and mat. these 50+ year old bodies are getting really degraded and are giving people fits. always do what has worked for you.

0grandmastercorvette

DO NOT gelcoat SMC. But you can apply polyester primer over it without any problems. With proper sanding and prep.

Gelcoat is NOT compatable with SMC, BUT...polyester products are able to be applied to SMC because most of the body fillers out there are polyester based....and they are made to go on SMC along with many other materials. IF you try to use an epoxy based filler/adhesive, ( excluding West MArine epoxy resin...becasue it is resin...and has different properties) you can and often times run into a swelling issue due to it being solvent sensitive and many these epoxy adhesives are made to be applied under a panel so they do not come into contact with solvents or have to be ground down so a filler can be applied over them ...which is more than likely going to be a polyester based product. Your statement is very misleading. Just wanted to clarify that polyester products can be applied over SMC...JUST DO NOT APPLY GELCOAT ON SMC.

Just because GM didn't use gelcoat on the pre-SMC Corvettes during PRODUCTION does not make it a wise product to apply. They corrected the some of problems with the press-molded fiberglass by coming out with SMC. Many choose not to apply gelcoat due to not having the correct type of application equipment or do not know how to correctly apply it or have found a product that works for them without having to deal with using gelcoat.

For you guys and gals out there that are going to paint your Corvette and it is a pre-SMC Corvette.

If your Corvette is your "baby" or "pride and joy" and you want to make it as good of a paint job as possible.....Consider this...wouldn't you want to apply a product on the body that provides a solid shield of protection against enviromental/oil based issues. So that if you ....while driving....happen to run through an oil based product, and it slings up in your wheelhousing area and you DIDN'T KNOW IT. The sun draws it into the press molded fiberglass over time, and then one day out of the blue, while it is out in the sun....BAM...you see bubbles in your paint. I have seen it and had to repair it and also this problem can occur due to excessive use of silicone tire dressing, brake fluid leaking and also an air compressor leaking oil on the underside of your hood......even on SMC Corvettes. The problem is that many of the products used in place of gelcoat can not be applied thick enough ( because many of them can't go 20 mils thick) and harden up well enough to prevent delamination when a substance it introduce from the underside of the panel. Gelcoat can deliver a protection to your fiberglass that is like no other product.....PERIOD! At 20 mils thick, it can hold a shape very well and be solid.

Last but not least:
I have performed so many tests on the products out on the market that I USE or have considered using that I know what they will do when subjected to brake fluid, paint stripper ( containing methylene chloride), lacquer thinner, silicone tire shine, water, engine oil, transmission fluid, gas,degreaser and aluminum cleaner/brightener. Gelcoat is by far the one product that fights the best against all of the products listed above WITHOUT breaking down or becoming liquid again. And the harshest of all of them is the paint stripper.... and it does quite well on not breaking down.

Use what you wish...but for me ....if I was contracted out to paint your Corvette...and it was a pre-SMC Corvette...it would be GELCOATED. Part of my mission statement for my business is... "offer nothing but the BEST for my customers". And if they choose otherwise....at least they were offered the best.

Wish ALL of you the BEST,
"DUB"

roger55

Personally, I would epoxy the fiberglass before applying polyester filler and that would be SMC or pre-SMC. And, concerning SMC, why someone would use a product that is known to be incompatible with another go ahead and do it is a puzzle to me. Not something I would choose to do.

Weren't you misleading when the OP posted a question about a '78 (SMC) and you answered the way you did?

I understand we disagree, but I believe the "best" on pre-SMC would be epoxy on both sides of the panel. I have used spray gelcoat and don't believe it is the best. It is also a lot harder to use.

0grandmastercorvette

I have been doing this for a LONG time and have NEVER had an issue with what you are concerned about. I HAVE talked to some of the chemists, who were in the lab, creating some of these products and talked with them extensively in great detail to find out actually how far one can "push" the capabilities of the product and actually find out what occured in their tests that makes it so it can be used on pre-SMC or SMC panels. WE AGREE TO DISAGREE HERE.

By all means if you can reference to what this statement means...and you are correct...I will gladly apologize or clarify what I meant if it did not seem to make sense to those that are not in the profession, or if I ACTUALLY am WRONG in written text that I wrote. I gladly wait for your response to what you read, and what it meant to you that makes you feel that I am "misleading".

Yes , gelcoat is harder to use. So we actually agree. It takes time and the know how to apply and use it correctly...which isn't hard to do if you want to take the time. Just because it is harder to use does not make it a good choice also. We have different ways of doing things...which is fine. So if you install an aftermarket front clip or body panel that has been gelcoated during the manufacturing process...are you going to sand off the gelcoat down to the handlaid fiberglass and then apply epoxy? OR ...leave teh gelcoat alone because you know that it has a very durable protective coating on the fiberglass.

Something for you to look into...which will be a bit hard to do because you have to find the "right" person who knows the product VERY WELL and not someone who reads off of a sheet. See how long it takes... for instance PPG DP-90 epoxy primer to TOTALLY cure. You may be shocked in what you find out...because I know you won't believe me...because I know how long it takes. That is if you really care to know it at all. And the TOTAL amount of time it takes to cure can change some issues in a paint job over time. I use it, it is a great product...but it is not the "magical" product for every repair. It also has its limitations.

I am cool with you and your views...really I am...and if your work is awesome and gives you no problems...why would you change your views and procedures. Just like me...have seen problems...changed.....and now no more problems...so why change again.
"DUB"

roger55

Sorry, I thought this was pretty self explanatory. In the OP's original post, he was asking about a '78 (which is SMC). In your first response, you recommended to him to use gelcoat. Then in your follow up post, you said "Just wanted to clarify that polyester products can be applied over SMC...JUST DO NOT APPLY GELCOAT ON SMC."
So, that does need clarifying since I interpret that as a contradictory statement to the recommendation in your first post.

Enjoyed the discussion. These differing opinions are what makes things interesting and allows everyone to learn.

Roger

0grandmastercorvette

I CLEARLY understand the how it can be read as a contradiction that I wrote in quotation marks above.

I WILL CLARIFY this when I get back to work on Monday and respond with an answer. I do not have the technical /chemical information at home...and do not want to make another error.

For me...Life is often times like the old game show where when you answered the question correctly, a section of the puzzle was revealed and began the making of a picture puzzle that you have to solve in order to win the game. Well, often times I feel that I can solve the puzzle but, with information from many of the forum members and others in my life, further fills in the puzzle correctly which changes the outcome of the answer....which I thought I had the answer. Life is full of knowledge and wisdom from others.

I have also enjoyed your input and discussion in this post along with the others who posted imput also.
"DUB"

0grandmastercorvette

I am responding to the issue if polyester products can be applied over SMC. After talking to the a knowledgeable tech for Fiberglass/Evercoat and also Molded Fiberglass Products. The only concern they stated was that EPOXY based adhesives must be used in STRUCTURAL repairs for bonding which they stated was the primary concern from GM. Also that the early SMC is different from the SMC from 1984 to current. Deals with the resin makeup and the ealier is "softer" so to speak. BUT when it comes to applying a filler on SMC...A polyester product works fine...even without having to apply a layer of epoxy primer on it BEFORE applying the filler. IF you have any doubts . CALL Fiberglass/Evercoat and ask the same question I did and wait for a return call from somebody who knows their stuff. It does get quite technical and chemically informative...but the answer will be the same.

But once again...if the way you are doing it is working for you...great...But like I mentioned...I do not epoxy prime anymore before applying a filler, and have NEVER had a problem with the Fberglass/Evercoat Vette Panel adhesive/filler from failing and delaminating.
"DUB"

wombvette

I agree DUB, it will work, but I would recommend erring on the safe side and not using it. Be careful of recommendations of some manufacturers like Evercoat. Sometimes you are talking to a lab or PR person who has NO experience in the real world of body work and painting cars, but has a vested interest in selling product. They also recommend their Featherfill product for use over old paint, and that one cost me a bundle years ago when it first came out.

0grandmastercorvette

I agree with you about making sure that the person that you talk to is knowledgeable. This guy had over 20 years in the business. He was only giving me facts of how he knows is products adhere and not trying to push any one product. This conversation I had with him was strickly on the chemical level along with the other company who basically confirmed his comments due to the amount of shops in their area that use the polyester products, did not have issues with cosmetic repairs.

Being cautious is a great way to make sure that you do not have problems...but I clearly understand why you feel the way you do...but being bit by PPG epoxy primer (which they re-formulated years ago) cost me in a few jobs back when it was formulated as a 1:1 ratio, which also back the it was NOT designed to be sanded, and when it was sanded it was soft and gummy and balled up on the sandpaper, and that is why I do not use it as the first layer on SMC any longer. It takes so long for it to get to total cure, I was not comfortable in using a product that was still curing when I was attempting to apply a product that gets harder than it, and feathering it was a total pain.

If this works for you...I am glad you have figured it out. For me I have found other procedures that work out well without any come backs or failures that I have to warranty.
We are basically choosing two different paths of repair that appear to have teh same conclusion. Award winning results...which I can prove on my end....and I am sure you can also.
"DUB"