Stain, paint, etc. does have a shelf life. As with anything we use there is a good, bad and ugly. Good is using the product as recommended by the manufacturer, bad is taking it to the limits and the ugly is using a product when you know it is bad! I have actually tried and sucessfully used film that was over 20 years old. It worked, but not good. If you see curdled paint or stain, Please dispose of it properly! LOL Good thing for us old people, they use us till there is little left!