I don't do a lot of fiberglass work but occasionally a job will call for it. The fiberglass resin and hardener will sit on the shelf for 1 to 3 years before I need it and it always gives a problem when I try to use it. It just won't get hard (no, this is not a sex therapy question!). I bought new hardener (NAPA) and tried that with the old resin but it still will not set up. Can the fiberglass resin go bad? I hate to buy a quart when all I need is about 3 tablespoons. Thanks