Corvette body work

[mike cobine]

I should add that this is for

1. original Corvette fiberglass fender panel

2. Avanti fiberglass nose panel

The second one is a guy I saw on another forum who has a big problem. Big spot of DOT 5 brake fluid on the nose and it seems to be spreading.

The first is that I managed to spill some on my '68. The panel is stripped to the red primer and the dark gray coating, unfortunately, not painted. I'd like to be sure it is out before painting.

[John M.]

Re: Corvette body work

Dennis,

I use The Ecklers gelcoat after all bodywork is done, and before applying any primer. Keep in mind, that gelcoat ONLY bonds well to either fiberglass resin or body filler. These two products are polyester based resin products, and are the same composition as polyester gelcoat. The Eckler's gelcoat is a wax-layer gelcoat. That is to say, that there is wax in the gelcoat that will rise to the surface and form a curing membrane after spraying. There are also gelcoats that can be sprayed on and then have a coat of PVA sprayed over top of it to act as a cure layer. Boat people usually use the PVA cure layer product, and it is probably eaiser to use, but I am a creature of habbit and I will probably stick with the wax-cure product as long as it is available.
If you spray either product over old paint or primer, it will not bond properly.

Gelcoat will not fully cure unless it is kept away from contact with air, and that is why a cure layer is used. You must spray the material sufficiently thick to assure that wax will rise to the surface to seal off the surface.
This the real advantage to PVA cured gelcoat in my mind, since the PVA is sprayed as a seperate layer, it is easy to assure a sufficient cure membrane.
PVA also will remove with warm water, while the wax layer will have to be sanded away with 80 grit wet-or-dry. This issue alone may someday make me switch to PVA cured gelcoat.

After the gelcoat is cured, You sand it to remove any wax from the curing layer, and any pronounced orange peel. Keep in mind, that the purpose of this material is to seal the fiberglass, and blocking the car should be avoided at this time. You do not want to sand off any more gelcoat than is necessary to get it smooth.

I then will spray Slicksand primer surfacer. It is also a Polyester primer-surfacer that has very high build properties, and I use this layer to block sand the waves out of the car.

I then go to a urethane primer/surfacer and spray a couple of coats on, and then wet-sand with 600. at this time the car is ready for color. I used to use Kondar or a similar Lacquer primer under lacquer topcoats, but I finally realized that urethane primers were a better choice on all type of top coats.
A lot of guys use PPG K36, but I use NCP 271. I don't think that NCP is any better, but I paint a lot of steel panels as well as fiberglass, and the NCP is a corrosion resistant primer. It is just easier to only stock only one group of primers and hardners in the paint cabinet.

A lot of guys will also skip the Slicksand step and go right to the urethane primer, and that is fine too. For a real original looking car where you do not want to remove all the waves, you are probably better off skipping the Slicksand. I like to make my cars as slick as possible, and the Slicksand gives me the fast build to allow real agressive blocking. You end up with a good portion of the material on the floor of the shop after sanding, but boy, can you make a body straight with it!

Regards, John McGraw

[John M.]

Re: I should add that this is for

Mike,

I would think that Acetone would help in diluting and bringing the fluid out of the glass, but I would not hold much hope. I worked on a hood that had DOT 3 on the backside of it, and I never got it to where it would bubble the paint after a few month. We finally scrapped the hood and put a new one on, and gelcoated the backside. I do not think that DOT 5 would penetrate near as much as DOT 3, and might be able to be pulled out with acetone. The nice thing about DOT 5, is that if it takes paint or gelcoat, it will probably be OK. The DOT 3 will take paint fine, but will blister later, but the DOT 5 should fisheye imediately if it is present, if it does not, than is probably will be fine once cured.

Regards, John McGraw

[mike cobine]

Re: I should add that this is for

So if I just add some fisheye killer for this section, you think I'd be ok? After cleaning the heck out of it, of course.

[John M.]

Re: I should add that this is for

Mike,

My guess is that if you can get the paint to lay down, it will probably stay down. There is nothing in the DOT 5 fluid that should attack the paint like DOT 3 does. If there is much Silicone still there, all the fisheye remover in the world probably will not help, but if the surface is clean, I would take a chance.

Regards, John McGraw

[mike cobine]

Re: I should add that this is for

Thanks, John.

I modified the flares on my race car years ago, using a silicone mold release on the originals. As such, around the race car it became standard practive to use fisheye killer as you never knew where silicone had been.

[Chuck S.]

Re: How Much Heat Can a Fiberglass Panel Take?

I was thinking it was in that temperature range, but now that I think about it, the temperatures for baking factory paint on fiberglass is somewhat lower than on metal-bodied cars. Maybe someone can remember what temperature GM baked the Corvette paint...that would be about your maximum.

A visit to Lord Fusor's site showed their SMC heat set adhesive taking a maximum of 180 deg for 3 hours, but that may only be for adhesive performance and unrelated to substrate maximum.

I have had fairly good luck using lacquer thinner in repeated wipings to remove FRESH oil spots if they were not yet too deep. Maybe it is still down in there deeper, but at least I couldn't see it on the surface anymore. The problem with using lacquer thinner, or any very light solvent is it flashes (dries) before it has a chance to really soak into the fiberglass. Acetone may not be quite as bad as lacquer thinner in that regard, but may give up something in effectiveness as well.

[Chuck S.]

Re: Corvette body work

I fought that K36 battle a couple of years ago...If you go with K36, you'll need a big nozzle (about 1.8mm-1.9mm), and don't try to catalyze more than a cup at a time. After an initial shaking of the can to mix all the heavy stuff, you want your cup quantity "stirred well, not shaken" after putting in the catalyst.

[John M.]

Re: Corvette body work

What Chuck says is true, and it holds true for the gelcoat or the NCP 271 as well. You will really need a gravity feed gun or a pressure fee gun with a 1.8 mm or better nozzle to shoot any of this stuff well.

Regards, john McGraw

[mike cobine]

Re: How Much Heat Can a Fiberglass Panel Take?

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.


In the case of original panels with this hardness, what do you think of the chances of actualy penetration of fluids into the panel?

If the gelcoat you apply seals them and keeps stuff out, then an original panel that has its own built-in seal should do the same, correct?

[Chuck S.]

Re: How Much Heat Can a Fiberglass Panel Take?

No gelcoat was used on original panels. John is describing a gelcoat "effect" where the accumulation of resin at the mold surface made the part surface a smooth replica of the mold. The problem is there are also glass mat fibers at or very near the surface...any oily substance applied to the surface, and left to soak, will probably follow the fibers down into the thickness of the panel.

My interpretation of Rick Snow's experience above was that gelcoat is NOT a barrier for light solvents trapped inside the panel. I expect gelcoat will work somewhat better for heavier oils simply because of the much higher vaporization temperatures of oils. It's vapors under the paint that are causing the bubbles or "solvent pop" IMO...not the migration of liquids. Gravity would be working to pull pure heavy oils down into the panel...in the case of refrigerant oil, I think the "solvent pop" effect is from R12 dissolved in the oil, not the oil itself.

[Terry F.]

Re: Corvette body work

My theory on what happened. First off, fiberglass is next to impossible to paint. GM probably knew that back in the good ol days. Shimmershines and corvette immage are only making panels that look like original panels and that is about it. It is my understanding that original panel were made with a special heated press that allowed them to use less resin than what is being manufactured today. In original panels, I believe moisture moved in and out of the panel much faster and with less resistance to the underside of the panel. When gas pressure met with the resistance of the surface paint/primer, it stopped (most of the time). Chemicals in the panels will always take the path of least resistance when trying to escape. That is why they want you to gellcoat. Taking a fiberglass car from a cool environment to hot environment pushes this process to the limit. Gassing off of the newer panels results in moisture moving primarily in two directions trying to escape because of the density of the fiberglass. The problem is only minimized when you gellcoat sufficiantly enough to prevent the process. My humblized opinion only.TERRy

[Terry F.]

Re: Corvette body work

I would not seal the underside of the panels. If anything, lightly sand them and open up the pores so the the moisture can move out of the panels. If you seal it, you will force the two surfaces (the inner surface and the painted surface) to compete with each other. The moisture will take the path of least resistance. I have also found original panels to be thinner compared to reproduction. So, the greater the distance the moisture has to migrate to get out of the panel, the more more vapor pressure that will be felt just under the surface of the paint/primer. Steel body panels don't have to deal with this at all. Fiberglass is simply the worst, most terrible material you could put a paint coating on. Granted, no one wants to gell goat there car to death but that is about the only solution because it has greater density than the reproduction panel and will act as a brick wall when the moisture tries to move in that direction. I believe my comments explain why you saw the bubbling only on the reproduction panels. Terry

[John H.]

Re: How Much Heat Can a Fiberglass Panel Take?

Chuck -

The peak temperature original panels saw at St. Louis was 280*F, in the first prime oven (60 minutes). Next-highest was in the final topcoat (partial) reflow oven, 250*F for 45 minutes. That's why Corvettes had to be polished to bring up the luster - the fiberglass panels wouldn't take the full reflow heat.

The same DuPont "magic-mirror" lacquer topcoat paint in the steel-body plants was reflowed at 325*F-350*F and didn't require polishing.

[Chuck S.]

Re: How Much Heat Can a Fiberglass Panel Take?

That's about what I thought on curing temperature, John, but I didn't want spread lies. Thanks for the feedback.

When I did the VIP tour at Bowling Green, I thought Kevin, the GM guide, told us they cured the BC/CC at 250 deg, and that metal-bodied cars were typically cured at 350 deg. He went on to explain that SMC panels wouldn't take the heat like metal. When you think about it, 350 deg, even 250 deg, is pretty hot.