Repairing cracks in the rear deck

[ozvet350]

Father Larry,
It is again time to come to you for some clear and accuarte information. I have all of the paint off my car and am getting all of the damage repaired. The guy who is doing the work has come across a small problem getting info on the best thing to use to repair some cracks in the body. We are working on a 1970 coupe with a 1975+ front clip.

Can you give us some help with the best stuff to use to repair cracks in the body work. So far we have been trying to fix some cracks in the area of the vents behind the rear window. Of the assorted stuff so far none has been holding anywhere near good enough. So any hints and products that you can suggest would as always be gratefully accepted.

Regards
Max Brown (from Australia)

[fatherlarry]

Can you post some pics of the cracks. That would be helpful. Also, how deep are the cracks? Are they surface cracks or do they go all the way through? We can go from there.

[ozvet350]

Father Larry,
I have sent to pictures which I will explain. The first is of the rear deck area between the vents where the crack is all the way through as you can see. The send is of the front fender where I hope you can see the cracks around the dark area in the middle of the shot. The dark area is a test of a resin to see what sort of bond we get and the cracks are surface. I have two questions from my guy doing the repairs as he does do fibreglass work, but not cars and definately not Corvettes.

1. What surface preparation is required.

2. What resin system should we use to get the best bond of a patch.

So please do not think you would be belittling us by being as simple as possible with your answers. We are trying to make sure that we get the best results so that my new paint job will not have any of these cracks reappearing in a year or two.


Thanks for you Aussie friend Max

[ozvet350]

Father Larry,
Here is the second shot.

[fatherlarry]

It looks like the one on the fender is below the factory joint bead and let's assume that it is all the way through.

As far as materials, I would buy a fiberglass clear resin with liquid hardner, and fiberglass sheeting which can be purchased at either an auto body supply store or a boat marine store. I would also buy some shredded fiberglass to mix in with the resin.


Let's start with the fender. I would cut a patch out of the fiberglass sheeting, 3 -4 inches larger in diameter then the crack. Get 40 grit sandpaper, or a small air grinder and grind the inside of the fender the same diameter as the patch, so that the patch will fit into it. Try not to go through, but indent a little so the patch fits right in. On the outside of the fender, try to grind open the cracked area to create a concave V shape so that the resin will penetrate through to the other side when applied. Grind around the cracked area on the outer surface of the fender around 2-3 inches with the air grinder disc, leaving it very rough. Blow out and clean inner and outer surfaces thoroughly. Mix your resin with the hardner, get your patch, dip it into the resin (wear gloves), apply the patch on the inside of the fender and with a 1 1/2 inch brush or 3 inch squeegy smooth it evenly on the inside. It's almost like patching a crack in a wall. Work quickly because the hardner will activate and starts to get hot and hard fast. When applying the liquid hardner, try not to add too much, because it will harden too quickly, but add enough or it won't get hard at all. Just read the directions and follow. I would experiment with the hardner and resin first before applying the patch. When you feel ready, then apply to inside of fender. Once you see it starting to get hard, get ready for the outside. Now mix your resin with hardner and mix in the fiberglass shreds and apply to the outside surface. Use a squeegy and your first application should be pushed in lightly so it joins with the inside patch. Then apply a nice even coat on the outside. Let sit for an hour or so, and then sand the inside of the fender first, where the patch is, starting with 40 grit sandpaper and finishing off with 80 grit sandpaper. Try to leave the inside smooth, so it doesn't look like any patch was put in. Then put a nice tight coat of autobody filler (also known as bondo) inside the fender to fill in any sand or grind marks. Don't forget to clean or blow out area before putting bondo. Now block out the outside of fender, using the 40 grit for the first cut and 80 for the second, just like you did on the inside of fender, but finish the outside with 100 grit sandpaper, to leave a smooth finish which blends in with the fender. Blow out and clean and then put a nice tight coat of bondo on the outside of fender. Block out bondo on inside and outside fender with 100 grit sandpaper, when bondo dries. Apply same process for the rear crack.

I hope this helps. I'm sure the autobody supply store that you buy your materials from will also be able to recommend some good products and will be able to give you some finishing tips. There are a lot of materials out there and a lot of different brands. I would check with some autobody shops and see what materials and brands they use.
:smoke:

[ozvet350]

Father Larry,
Thanks for the great rundown on what to do, I will pass it onto my guy and he should get great assistance from it.

Thanks
Max