Fiberglass repair

[Jack A.]

I have a 61 I am restoring. It was painted about three yeas ago. I looked great. All of a sudden all of the bonding/seamed areas appear to be moving. That is probably not a good description but it is the only one I have. They have raised in some areas and sunken in others. Very little but discernable. I was wondering if there is a thread or information source for the proper treatment of these seams Some are all in the hood area by the windshield and are factory seams. These are the ones that sank a littel. I have one area where there was a repair. These seams are all at least 30 years old and redone by the local very reputable shop. It was not Bondo. Any help would be appreciated.

I should add that the car has been in the shade for the last two years and only recently exposed to our very harsh Florida heat and sunshine. It is Red.

Jack Alexander 35730

[Richard M.]

Re: Fiberglass repair

Jack,

Can you post some photos of the areas you're having issues with?

You said some seams are in the hood area by the windshield. A bit confusing. There were no factory seams in that area, other than where the surround is bonded to the firewall at the rear lip of the hood gutter. Is it possible that someone installed a hand-laid one piece front end? They use seams at the windshield cowl along a line into the outer rear corners of the hood gutters. If so you would see the seams from under the dash.

Do you have a accurate history of the bodywork, old photos, etc? That might help understand what's going on.

Rich
p.s. a one piece front end showing the top seam location.....

[Philip P.]

Re: Fiberglass repair

I think this is a normal situation with the older cars, as long as they are not delaminated. There is a section in the Corvette Restoration Handbook that talks about it, this is a good read if you do not have it. My car has one older repaint and if the sun is right you can see a couple of the the body seams, think they call it "patina".
Phil
1960/230

[Domenic T.]

Re: Fiberglass repair

Jack,
It sounds like what we called photographing, (shrinking) especially if they didn't use a 2 part primer such as epoxy primer.

The material used to surface the paint (primer) shrinks as time go's on. To avoid that I use a good 2 part epoxy primer and let it cure for over a week before sanding it to prep the surface for paint.

I have found that fillers like bondo and primers that say they don't shrink actually do shrink if they are sanded without a complete cure.

Now laquer primer dries and WILL shrink unless it dries a long long time.

Thats where we got the term '' photographing'' it was a picture of what was there, a picture of what it looked like before using a primer/surfacer.

DOM

[Steven S.]

Re: Fiberglass repair

If you are talking about factory seams, you are seeing the bonding adhesive that was used. It is about 80% cured when car is built. Over time, it will further cure and shrink. Heat will make it cure further. If your car has not seen a lot of sun/heat in the past and is just now getting it. The bonding areas are further curing and shrinking.

All fiberglass products shrink with time. Dark colors will be worse then light. The fiber pattern seen is the resin shrinking and the fiberglass mat/ chop not shrinking resulting in what is called in the industry as "print through". Gel coat helps eliminate this because it normally is applied at 20 to 30 mils (1000's of an inch) thick. Epoxy primer may not stop this due to it being too thin on the car (1 to 2 mils).

Steve

[Domenic T.]

Re: Fiberglass repair

Steven,

I have to disagree, Gell coat is a enemy of glass on vette it cracks.

Thats why all the resin is squezed out of the panels by the inner and outer mold when they are made.

I will say that epoxy gell may do it OK in small areas but fiber glass resin will crack.

Boats use gel coat, take a look.

The GM rep told me years ago that the strength is in the glass not the resin.

I think I can post pictures of my 63 where someone put gel coat on a repair and it is all cracked. I am in the process of taking all the bad work off the car.

DOM

If you are talking about factory seams, you are seeing the bonding adhesive that was used. It is about 80% cured when car is built. Over time, it will further cure and shrink. Heat will make it cure further. If your car has not seen a lot of sun/heat in the past and is just now getting it. The bonding areas are further curing and shrinking.

All fiberglass products shrink with time. Dark colors will be worse then light. The fiber pattern seen is the resin shrinking and the fiberglass mat/ chop not shrinking resulting in what is called in the industry as "print through". Gel coat helps eliminate this because it normally is applied at 20 to 30 mils (1000's of an inch) thick. Epoxy primer may not stop this due to it being too thin on the car (1 to 2 mils).

Steve

[Steven S.]

Re: Fiberglass repair

I agree, gel coat is not made to be a post painted item, but the fact still remains that it does lessen the print through from happening. I work for a major gel coat manufacturing company and would say using as a post coating is problematic since it is made for putting in the mold not as a paint. However several people have successfully gel coated a Corvette and had good results. Understanding how gel coat works and using proper catalyst and film thickness when applied is key. applying like paint will give poor results. Also the gel coat when post painted is mechanically bonded to the fiberglass vs chemical bonded as when applied in a mold. This means that it can peel as you have experienced unless the surface is clean, wax and dirt free and has a "tooth" to it so it can bond..

Steve