Corvette body work

[Brenton Mitchell]

I installed a new jig front end, I also replaced the rear quarter panals,
All the seames have been v-grooved, glassed and shaped with body filler,the car
has been sanded with 80 grit paper,I am trying to talk my self out of gel coating the car, what are your recommendation.

[John M.]

Re: Corvette body work

I gelcoat all my bodies, and I will probably always do so. There are only 2 makers of replacement "correct appearing" fibergalss, and Corvette Image will probably not warranty the panels without using the gelcoat. If you are using their panels, you should have recieved this information as well as a caution abot using urethane or Epoxy primers over the bare panels. I use Semerschiems panels, and even though that they gelcoat both sides of their panels, I still gelcoat my bodies after all bonding and body work is done. I feel that it is unsurpassed for sealing the bare glass and body work.

I am not saying that you can't get good results from using a 2K primer right over the body work and bare glass, but I have been getting excellent results for years with gelcoat, and don't have any plans to change what has been working. The fact that the manufacturer of panels now strongly reccomends the use of gelcoat to avoid the blistering that has become almost common place with their panels, speaks volumes, in my opinion.

Regards, John McGraw

[Richard S.]

Re: Corvette body work

Brenton,

I used Corvette Image panels on my 67 and we gelcoated the car before painting. Last summer we had to leave the 67 outside the garage for a few days while we had work done to the garage. The car sat for three days with two car covers on it in 80 degree heat. When I took the covers off the Corvette Image panels had tiny bubles coming through the paint. In talking with several NCRS experts at various meets around the USA about what happened it would seem that because we did not seal the underside of the panels (we left them bear fiberglass) the humidity went right through the panels from the underside and came through the paint. I hope this information will be useful to you in your time of decision. Feel free to contact me for more information or if you have any questions.

[Dennis H.]

Re: Corvette body work

John, I am in the process of doing my 64. I have it stripped. Please elaborate on the procedure and products you use after the car is stripped up until you are ready to apply paint. Thanks Dennis

[Chuck S.]

Re: Corvette body work

Hmmm...I dunno, Rick, but something doesn't add up with that explanation. Are the experts saying your mistake was not gelcoating the inside of the panels as well?

I'm a great fan of Corvette Image...if I ever have to replace a panel it will be a Corvette Image part, but difference in manufacturing methods must be the cause of this problem IMO. This is not a criticism of Corvette Image; it simply a statement of reality and something we have to live with using reproduction parts.

General Motors suppliers made panels that didn't require gelcoating on EITHER side. Unless those car covers were like shrink wrap applied by vacuum, the humidity was exactly the same on both sides of the panel...there was no differential in relative humidity to drive water vapor across the panels and force your paint up. Double car covers in the summer sun more likely generated enough heat in an unventilated environment to vaporize residual solvents in the FRP. JMHO.

[Richard S.]

Re: Corvette body work

Chuck,

I thought of that as well. The problem is that ONLY the Corvette Image panels blistered. The car was in a shaded area most of the time so I didn't feel the sun was a factor. I sure should not have put two covers on the car though. I'm told that each original panel had blackout material applied to the underside of the panels. We left the panels bare on the underside. The clearcoat paint and gelcoat would have prevented any penetration from the top side of the panels.

[Chuck S.]

Re: Corvette body work

"...The problem is that ONLY the Corvette Image panels blistered..."

Precisely my point...When GM suppliers made the parts, they were press molded in steam HEATED molds. I suspect aftermarket manufacturing methods are not cooking as much of the volatiles out of repro fiberglass parts as Rockwell, et al.

I don't think black-out on the backside of factory panels has any affect on this problem...there is plenty of original panel area that's not blacked out. On my 70, the entire rear fenders behind the wheel well are exposed natural fiberglass from top to bottom, not to mention the deck and tail light panel. Fresh air circulation in that area is also unimpeded. If original panels were going to have this blistering problem without blackout, those parts of the cars would look awful.

[Richard S.]

Re: Corvette body work

I'm not sure I'm following you here Chuck. Are you telling Brenton that if he uses aftermarket panels gelcoating both sides of the panels will not prevent solvents from coming up through his paint??

[Chuck S.]

Re: Corvette body work

Not at all. I'm not telling anybody anything...I'm trying to determine the likely source of your paint bubbling problems with reproduction panels. My conclusions from this thread and my own reasoning:

(1) You must use gelcoat on reproduction panels unless you want problems...Corvette Image says so. However, from your own experience, using gelcoat is not enough to guarantee not having problems.

(2) Use of gelcoat on original panels may be of questionable value unless the original fiberglass has been contaminated with oils or solvents since it was originally built. That is...unless someone can suggest another reason it should be done.

(3) After completing body repairs, and BEFORE gelcoating, you may want to leave your car out in the sun as long and often as possible (maybe with multiple car covers) to help remove residual solvents from reproduction panels and bonding adhesive before commencing painting.

(4) Atmosphereic humidity and panel black-out are irrelevant to this problem. Heat from the sun and residual solvents left in the resin, especially under multiple layers of car covers, may be a contributing factor...of course, I could be all "wet" on the car cover idea; camel jockeys wear a lot of clothing in the desert for the insulating value.

"Whither Gelcoat?!!" It's a question I still have to answer for myself. No matter how many times I read these "gelcoat" threads, I can never get enough information to convince me of a decision in either direction. I've decided in each direction at least once.

[Warren L.]

Tiny bubbles

sometimes the tiny bubbles are cause the panel was defective. I know of one case where it popped during buffing. Turns out that the panel was defective in manufacture. Quite likely it would have popped when it was sitting on a hot day at 170 or more degrees surface temperature which I have seen and more on my old stationwagon

Warren

[mike cobine]

How Much Heat Can a Fiberglass Panel Take?

Many talk about leaving them in the sun to heat and bake the various items out, but if you were to speed up the process with heat, like heat lamps, radiated heat, etc., how much heat could you safely give a fiberglass panel before you begin new problems of the panel getting messed up?

Do you think you could bake out brake fluid, like the DOT 5 brake fluid?

[Chuck S.]

Re: How Much Heat Can a Fiberglass Panel Take?

Mike, I don't know...I have seen the max temperature for heat lamps on repairs somewhere. It may have been for SMC on Lord Fusor's site. Check some fiberglass repair books; I looked in Eckler's book and use of heat lamps is not covered. As I recall, the max temp I saw was higher than I would have thought, but it was for short periods, say an hour or so. Most of us amateurs are usually more interested in how we could slow curing down, rather than speed it up.

As far as boiling out silicone brake fluid with heat lamps, or most heavy oils like refrigerant oil, I think you can forget about it...what's the boiling point of DOT 5 fluid, about 575-600 degrees?

[Philip C.]

Call some of the big restore shops around

the country and ask them about this prolbem your NOT ALONE BIG TIME!!!!!!!!!!!!! esp the ones in New York Phil 8063

[John M.]

Re: How Much Heat Can a Fiberglass Panel Take?

Chuck,

I think that the problem stems from the fact that the current replacement panels made by both CI and Semershiems, bear little resemblence to the original manufacturing process. The original process used steel, heated, matched dies under very high pressure. This process made for a very dense, hard cured panel that had a resin rich layer on both sides of the panel against the die. This resin rich layer is basically the same as what we get with gelcoat on molded parts.

My understanding, is that the current "press molded" parts are anything but. I belive that they are just molded parts that have a second mold pressed against the back side to smooth out the appearance. I understand that the process does not use the high pressure or the heated die that was used on the original parts. I know that CI warns about gelcoating both sides, and uses the same statement about moisture migrating into the porus fiberglass. They also caution about using Epoxy or urethane primers over the bare glass, as they say that the heavy solvents in both these products will migrate into the glass and cause blisters in the future. I know that CI has a bad problem with blistering in their panels, and it is their contention that following these steps will avoid the problems.

The panels that I get from Semershiems, are clearly gelocated on both sides when they arrive, and I gelcoat after any bonding, bodywork, or grinding. I have never had a car blister, and I have always used gelcoat. I do not know if it is because of the gelcoat or because I am lucky, but I am going to stick with gelcoat as long as I continue to have good results from it.

Regards, John McGraw

[mike cobine]

Re: How Much Heat Can a Fiberglass Panel Take?

DOT 3
Dry 572F 300C
Wet 298F 148C

DOT 5
Wet 356F 180C

Now most forget that "wet" means exposed to the atmosphere. (But since DOT 5 doesn't absorb atmospheric moisture, is there really a "wet"?) I think this is more a reference to contaminated, like exposure to air, rust, etc. So I think you could say that fluid soaked into a fiberglass panel would be contaminated.

Also, I don't think you need to actually boil the brake fluid, but the closer you got, the faster it would migrate out of the fiberglass.

So could you get a panel 300 - 350 degrees F or more? And would contaminating it with lacquer thinner or some other solution speed the removal?