It is never a good idea to thin epoxy with alcohol. It is to easy to trap water (alcohol absorbs water from the atmosphere even if you start out with pure alcohol) in the mix and then you get the rubbery result. The alcohol you buy in the drug store can contain up to 50% water, use denatured alcohol if you must use alcohol. This is even worse with the quicker setting epoxies. Remember, epoxy does not DRY it CHEMICALLY CURES. The suggestion of adding heat sometime helps but leaves a weaker bond if the mix was formerly contaminated with water. Heat, if not excessive, in itself does not hurt the bond and will speed up the chemical reaction or curing process.