MaineVette wrote:rbryce1 wrote:Learned from my 1st rebuild that fiberglass work shrinks, especially polyester fiberglass. Had to do shrinkage repairs for almost 9 months before I got them all.
Really? I didn't know that...
Time to do a bit of research...
I mostly had problems where new panels were joined to existing panels, where two panels were joined together or where we actually fabricated shapes directly on the car, the last being the worst. Had most of mine in the custom wheel wells (made them, didn't buy them) and where the hood was joined to the fenders to create the tilt nose and where the custom (custom designed and hand laid clip) front clip joined the fenders. From what I have seen of your work so far, shrinkage should be at a minimum, as you have not really done anything without bonding strips that I can recall. Polyester resin has solvents that must evaporate to cause the curing process. As it does this, the material shrinks, but not always evenly. I am not speaking as a chemist, but as someone who has witnessed these results, read in books as to why it occurred, and had to fix them (the last being the most significant!). I was also warned of this by the Corvette body man who did most of the custom work on the car. His name is John Jamison (
http://www.jamisoncustomcorvette.com/Default.asp ) and is one of the best Corvette bodymen I have ever known. I understand that today's epoxy resins do not shrink hardly at all, as there are no solvents to evaporate out, but a chemical bonding reaction to cause curing. I am using all epoxy this time. A bit harder to work with (very difficult to use a brush on mat and must roll out air bubbles) , about 3 times longer cure periods (I'm not in a rush to finish next week like a body shop would be) and costs 3 times more (the restore will cost about $18,000, so the extra 200 bucks is a drop in the bucket). Epoxy, I have personally witnessed on my own experiences, holds 10 times better than polyester and is 20 times stronger as well as more flexible when it needs to be. Epoxy will also bond to most any material. I used a plastic container to mix a batch and did not use all of it. After it cured, I noticed I had left the brush in the container. With polyester resin, I would simply flex the plastic container and the resin would pop away and be easily removed. I could not flex the container where the resin was, only above the resin line, could not pull the brush out of the resin, or even move the brush in the container. Eventually, after extremely hard pulling, the brush handle broke off of the metal frame, and the container, epoxy resin, part of the wood handle, the metal frame and brush bristles remained as a solid part. Say what you want, I'm sold on epoxy!! About 25 years ago, my floor boards were deflecting in front of the seats (where your feet go). I glassed that area with polyester and mat. The deflection was reduced (but not eliminated). Three months ago, during the repairs to my cage, I noticed the glass was separated slightly where the new glass joined the old floor. I pried on it, and POP, the entire new glass portion popped out, like it was made from a mould of the existing floor! It stuck really hard, but never really bonded. I know the floor was prepped correctly, so I can only conclude that there was something in the original fiberglass floor panels that the polyester resin didn't like to bond with. My floor boards were again able to be flexed about a 1/2" with pressure, and were cracked where the seats mount. This time I laid one layer of mat/cloth combined material (don't remember the actual name of it, got it at Fiberglass Coatings, Inc.) and epoxy resin and it is now like steel, absolutley NO deflection at all. Also used the epoxy mat/resin and a material Fiberglass Coatings sells called Superbond, an epoxy paste filler with the consistency near that of Vaseline (you can thicken it to your needs with a thickener they sell). Once cured, cannot pry it off, can sand/grind on it to form anything and does not shrink that I can see so far. My windshield frame was rusted through at the bottom, and I filled this area with Superbond. Was able to bond with the metal on the windshield frame perfectly, was able to shape in 3 dimensions to match the contour of the frame, able to re-create the lip that holds the windshield and came out perfect. Have photos. New metal parts for this were $400.00 (for 1973 and later, not available in 1968 design, which was different as you know. This cost me 20 bucks and 1/1000 the work and it can't rust again.
Well I'm done rambling, anything else you would like to know about what I have found, just ask. Back to work. I am rebuilding the passenger side #4 body mount today. Boy is that a chore. You don't know how lucky you were not to have to rebuild them, especially on a convertible like mine!! Just be patient before you paint. Drive it for 3-4 months in primer and look for shrinkage, fix it and drive it 3-4 more months. Repeat as necessary before you paint. You will not regret it. If it shrinks right after you paint, you will probably consider Hari-Kari after all that work!
Enjoy, Bob
