why risk it? smooth on is not to expensive compared to the glass, riser block and tapers. I keep mine inside the house and have used some that was opened 4 months earlier. it looked good and still mixed well. I opened a can that was at least year old, it only had about 5 oz in it, one of the cans had a strong "ammonia" like smell to it and had a skin on top, I tossed it.