ORIGINAL: da Rock
ORIGINAL: Charlie P.
Alcohol is hydroscopic and once open 100% soon becomes 95%. It sucks water out of the air. Iso 91% is about the highest stable concentration that is readily available in drugstores. 100% alcohol would have to come from a lab supply store and would cost plenty. Solvent and stove alcohol are about 91% also. Denatured solvent alcohol still has 3% water when sealed at the factory.
Interestingly detailed information there. How soon is soon, and when does it become 90%?
If you'd like to get a feel for how fast it sucks water from the air, weigh a can and open it. After however long you wish, close it and weigh it. There should be a rate of evaporation printed right with the rate of water absorption documentation and you could apply both to see just how fast your can chugged down the water out of the air.
Or you could simply use the least watered down alcohol you can find to start off with.
Depends on your relative humidity. ;-) My basement dehumidifier sucks about a gallon a day out of the cellar air and we have humidity to spare here in Upstate NY. But you are correct in starting with as high a purity as possible. Then again, I'm still not sure you can thin polyester resin with alcohol. Personally, I use acetone when I thin epoxy, but alcohol and lacquer thinner work also.
Here is a good discussion on thinning from the West Systems site.
http://www.westsystem.com/ewmag/14/ThinningEpoxy.html
And, if you don't believe alcohol sucks up water then let your glow fuel (80 to 82% alcohol) sit around for a year or so in a partially used jug.
