They do say cold causes shrinkage

I agree. The number that comes to mind is 12 drops of hardener per ounce for polyester resin. I've had good results using the west marine finish gelcoat with wax in the formula. Mixing throughly is also important. Once you think you've mixed it enough, mix it some more.

sm

http://www.youtube.com/watch?v=en-8SbhdF_k&feature=related

pretty good video on gel coat repair.
BTW it states 20 drops per Oz

What brand of hair spray?

1 oz of fluid is about 500 drops. If you are looking for a mixture:
1% = 5 drops
2% = 10 drops
4% = 20 drops
I use about a 2% mix for regular resin. I use about twice that much for gelcoat. Gelcoat takes longer to dry. Gelcoat is, in effect, resin, pigment (for color), and a thixotropic material. The additives retard the gelling properties of the resin.

If you really want to know and are interested do this experiment. I took some resin classes in college and one of the requirements was to see what resins, gelcoats and epoxies did with different hardener ratios. I took an icecube tray, put equal amount of the same product (ie resin) in each of twelve compartments, then catalyzed them with different amounts. Start with lower than recommended, say 1/2% and increase by 1/2% each until you get to about 6%. Do not stand too close, that 6% will smoke. See how long it takes for each to harden. Your hot one will harden in minutes and probably crack. The slow one may not harden for a couple of days. You will get a really good idea about how your resin reacts and know what you will be comfortable for you.

Dr. DeLave!!!

EXACTLY!!!

Is there a theory on slow vs quick hardening and strength?

I'm not aware of any. However, I've heard that using too much catalyst with epoxy can leave soft spots. Can't speak to the truth of it.

I can also tell you, from personal experience, that you certainly can add too much catalyst.

On one occasion I was very impatient, it was quite cold and I added lots more than called for.

The mixtures heated dramatically, then bubbled into froth and finally harden into a gooey consistency like messy foam.

It was very interesting to watch.

The final mess was (shall we say) less than useful so don't get carried away, as I did.

This looks like Dan! -kinda

The gelcoat hardening must have been related to the paper being in the panty er pantry..

Most likely the problem was not enough hardener. The other things were just a bit helpful. If you stir it well I am not sure it helps to dirty two containers. I personally only do small batches at a time so I do not waste it when it hardens quickly. I also use rubber gloves because the stuff is a pain to get off. You can also put "liquid gloves" on which keep the stuff from sticking to your skin.

What is the problem with using plastic? I use it regularly with gelcoat and polyester. Never had a problem. In fact I think I remember someone telling me that if you put plastic or waxpaper over it as it hardens then the wax stays in the polyester so the next coat will stick better.

I put cloth or chopped cloth on with polyester initially and then put plastic on, then I squeeze out as much resin as I can and then put a many times folded rag on top of that and then a piece of wood to hold it in place and then I put as many spring clamps to push on it as I can fit. This is to squeeze out more resin. My repairs come out excellent. Took me many a repair to figure this stuff out.

Anyone know where I can find carbon fiber in cloth or ribbon at a reasonable price?

Nice goggles, are those Barz?