Fibreglass Distortion

[SteveHsr]

A waviness has developed in a couple of areas in the hood of my Mark 3. It is subtle but easily seen in the glossy black surface and is about 6 inches across. My first thought was some sort of distortion due to heat, but one affected area is toward rear of scoop where there is very little engine heat. The wavy surface is both inside and out, so not just a surface defect. Car is always garaged in California with no environmental extremes. Car was painted and perfect 2 yrs ago.
It's abit of a mystery and would be good to understand before repaint. I would appreciate hearing if any of you are familiar with what I'm describing or have any ideas at all about the cause. Could it be some sort of delamination, which would suggest I replace the hood?
Your comments much appreciated,
Steve

[CRZN 427]

There is is a lot I don't know, but this sounds like "creep". Fiberglass seems to cure forever to get the last 1% (+/-) done. As a result the surface of large nearly flat areas will warp a little. In other places it might imprint on the support structure and leave waves in the surface above any structure that it contacts. You can see this in all kinds of fiberglass bodies including the 'Vetts. Eventually it might stop creeping. Different heat zones may also cause some similar distortion.

Regards Rick.

[mikeinatlanta]

People often use the word fiberglass, while it is actually a composite of fiberglass and resin. The glass is fairly generic, however, the overall characteristics are determined by the resin. In the case of FFR, they use a high quality vinylester resin that can easily handle your under hood temps if properly mixed and cured. The cure portion of this is where FFR doesn't quite finish the job, and anyone wanting a show quality finish really should. If the resin is only cured at room temperature it will never reach its full potential and the result will be minor movement and a reduced glass transition temperature (goes soft with heat). This issue is less common when the body is left to sit in the sun over a summer, but it will still never reach full potential without a proper post cure cook.

It's obviously too late for you, but others can minimize this risk by having the body placed in a powder coating over for a few hours at 150-160 before doing bodywork.

EDIT: With the heat generated by your motor and age, your hood is most likely stable now. At this point a repair should last.

[SteveHsr]

Thanks Rick, will connect your helpful info with Mike's.

[SteveHsr]

People often use the word fiberglass, while it is actually a composite of fiberglass and resin. The glass is fairly generic, however, the overall characteristics are determined by the resin. In the case of FFR, they use a high quality vinylester resin that can easily handle your under hood temps if properly mixed and cured. The cure portion of this is where FFR doesn't quite finish the job, and anyone wanting a show quality finish really should. If the resin is only cured at room temperature it will never reach its full potential and the result will be minor movement and a reduced glass transition temperature (goes soft with heat). This issue is less common when the body is left to sit in the sun over a summer, but it will still never reach full potential without a proper post cure cook.

It's obviously too late for you, but others can minimize this risk by having the body placed in a powder coating over for a few hours at 150-160 before doing bodywork.

EDIT: With the heat generated by your motor and age, your hood is most likely stable now. At this point a repair should last.

Thanks for the composite science. I assume the additional curing bake at 150-160 would add some insurance that I'm ok to repaint. Appreciate your help.
Steve