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I have some stress cracks around the headlight openings and hood inserts on my 69 and was wondering if someone could suggest the best way to repair these cracks. I have the areas stripped down to the bare glass and it seems to be cracked only on the surface. Is sanding the area down and then applying fiberglass resin without the mat an acceptable fix? Thanks for any help on this one.
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Re: C3 body stress cracks
Greg - this is a common area to get stress cracks. Personally, I would vee out the cracks, and use matt and resin, or, use a good grade of bonding adhesive/filler. I suspect if you just you resin as a gel application in a stress area such as this, it will come back again....Craig -
Re: C3 body stress cracks
I am not a body man but when my car was re done I had simular cracks and the body shop drilled a tiny hole into the end of the crack ( I was told that the hole would NEVER allow the crack if it returned to move past the drilled hole)they then veed out the crack and used resin and matting to repair it.They have not returned since.I had some cracks just behind my door handels That repair I was not around to see how they fixed but a short time latter they have returnedComment
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Re: C3 body stress cracks
Hum, The old drill a hole in the end of the crack method. Interesting, but useless. May even cause more problems than it solves. This is an old urban legend that the crack is going to run, like glass on a windshield. It just aint so. Dont do it.Comment
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Re: C3 body stress cracks
Thank You wayne for bringing me up speed on the hole in the crack information.When it was exspained to me it made perfect sence.Comment
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Stop Drilling
Stop drilling a crack in aluminum is common practice in the airline industry, but I can't say if it works with composites.Comment
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Re: C3 body stress cracks
Stress cracks are the thorn in every Corvette owner’s side. If you car doesn't have any.....just wait. Sooner or later they will show up somewhere.
There are body fillers available at most automotive paint dealers that contain very fine strands of fiberglass. (we call it "cat hair" here in the Mid West) This stuff works like regular bondo except it is kind clumpy and you typically put on more than needed and work it down after it sets.
You will need to relieve the stress cracked area in your panels at least a 1/16 of an inch deep. Taper the depth of the relieved area around the edges back up to the surface level about a inch surrounding the area. Use a hand held die grinder with a 2 inch dia. 40 grit disk for this surgery. You definitely need precision to prevent grinding completely through the panel.
Wipe the residual dust from the repair with a clean rag and acetone. Mix up the reinforced bondo and mash it into the repair area. Go ahead and work it down as much as possible and distribute the cat hair evenly across the repair. The resultant repair should be about an 1/8 thick and you will work it down to the car's surface later. I generally wait 24 hours to ensure that I don't "lift" the repair before it has a chance to permanently bond to the panel.
Finish along with the rest of the car with the primer surfacer of your choice.
Good Luck,
tc.Comment
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Re: C3 body stress cracks
Thanks guys! I think I'll prep the cracks like Tracy says but use the fiberglass and matt like Craig says. I'll leave the stop drilling to the aircraft structures guys.Comment
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Re: C3 body stress cracks
Hi Greg,
I did a frame off restauration of my 69 in 1998. I've found many stress cracks in the composite of the complete front end after grinding. A professional body shop with experience in Corvettes fixed them.
But now, after 5 years they came back - all!
I think the composite material gets older and brittle.
Next year I'll repair the complete frontend again ... and again and ...
Klaus Friedrich
GermanyComment
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Re: C3 body stress cracks
Thanks for the input Klaus. Do you know if the cracks are the old ones that came back or are they new cracks,but in the same general area?Comment
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