cracks reappearing in hood

[LanceB]

I recently had my 81 painted, there were cracks in the hood where the hinges are. My body man said he thought we were going to have to scrap the hood, but he was able to repair it and he buried aluminum sheets in the hood to reinforce it. The first month looked great, no sign of repair at all. I looked at it in the garage today and now there are outlines appearing, almost as if the fiberglass has sunk. Has anyone dealt with this before, and will it eventually go away with enough repairing?

 

[mike weyman]

if it's showing up now it will only get worse.i've done a bunch of stress crack repair on mine and only used fiberglass.i have nothing showing yet (6 mos)but the car has not been driven .it could be more noticeable since the paint hardened and is now actually thinner,allowing you to see the work.

 

[tomtom72]

Hi LanceB, If you see something showing thru the paint then the mechanical forces are too great for the local repair. I respectfully submit the following that I learned working at a boat body shop for 11 years, part time mind you just to help support my other bad habit. Any surface crazing (spider web like cracks) can be a result of the substrate loosing it's laminate strenght & integrity. Any GRP ( Glass Rienforced Plastic ) panel has a laminate schedule ( the type and # of layers of glass cloth saturated by resin ). If the panel de-laminates then the surface eventually shows some sign of the laminate layers working independently instead of together. I do not know what the laminate schedule and laminating methode is for vettes. I've heard so many things that I don't know fact from fiction. I would really have to know the particulars of an 81 hood to offer a useful diagnosis. However if a vette's body panels are pressure molded, that process I know nothing about and I would be of little use.

Please do not think that I am questioning the integrity of your repair shop's performance. I am not, however I have seen some well intentioned work done incorrectly on GRP. Boats are different than cars but working GRP has some universal basics that often are not known by people outside the marine field. If it's your pleasure PM or e-mail me I would be more than happy to discuss what I learned about GRP. Sorry for the long response, Happy Holidays, Tom

 

[CQRT]

Tom:
Just a quick compliment on the thoroughness of your reply - - I've learned alittle about good and bad fiberglass over the years from owning a couple of Sea Rays along with eight Corvettes.
Although we're never too old to learn, I feel frequently put off by some posters in this forum who take a "my way or the highway" kind of attitude without concern about the time, energy or pride individual owners might have in their work.
Thanks for a thoughtful, respectful explanation and while we're at it, thanks to the moderators and sponsors of the forum. Hopefully, Lance will get his hood squared around.
Best wishes to all for the holidays.
Regards-

 

[tomtom72]

Hi CQRT, Happy Holidays to you & your's also! Thank you for taking my response in the spirit I had intended. I have been the benificiary of so much kind help from my fellow members here that I wanted to give some in return. I guess we all feel that way and I think it's a reflection of our sense of community, which comes down from the top.

Anyway I would offer this after reflection today while I was washing my new toy. I had a C3, a 72 and I seem to remember the hood being a two piece design: inner & outer bonded together??? The hinge anchor points being two protruding bolts on the hood side then the hinge lever attached to the fender. I wish I had my 72 shop manuals. If I am correct about the bolts bonded to the hood, then the crazing on the painted side of the hood is a result of the "glue" that holds the bolts in place giving up. The only effective repair is to separate the inner & outer panels and see exactly what mechanical method was used to hold the bolts in place. Then having discovered that an appropiate method would present itself. The only danger when bonding GRP to metal is the bonding area needed to carry the load and the bonder must be up to the task. I just can't remember for sure what the underside of my 72's hood looked like! I do know from boats that anytime metal was used as a backing plate it was done only two ways: a stand alone backing outside & separate from the laminate or buried in a suitably thick laminate with some specialized stress distribution media as a buffer between the metal and the laminate. Sorry LanceB I have yet to do anything but think out loud! Tom