the amount of hardener you should add is proportionate to the amount of resin your using. it also depends on the temp. of the work room, how quickly you can work with it, and so on. if you add too much at one time, if will being to gell and harden before you can use it all. i usually do about 4-5 oz. of resin with about 1-2 good squirts of hardener. i would suggest just doing a small amount of resin with a small amount of hardener and just basically do a trial and error type experiment.