Everything has a shelf life even if left unmixed, it may be short or long depending on the product, but it can eventually "go bad". Look on the container, it will tell you its shelf life, after the shelf life is when it starts to break down. Everythings like this, that why if you hang out around paintshops and boat supply places you can score freebies or very low costies because they havn't use it yet or sold it and the shelf life is nearly up. It can still be used soon after the date specified, but after the shelf life is up you can't store it and use it down the line. It all depends on the product its still safe after the date to use it, but its not very long.
HK
