Shelf life once opened can hardener much longer than tech sheet tells?

[KevinPainter]

Recently i sprayed a primer with hardener which was already opened once at least 5 months ago. The result however turned out okay (the hardener itself looked okay too before i mixed it with the primer, no crystalization or something).
Tech sheets tell that once a can of hardener has been opened the shelf life is only one week tops. How is it possible then that there seems nothing wrong with the "old" hardener i used?
How can you tell a hardener has turned bad?

 

[Wydir]

Hmm if hardener went bad after a week Im guilty of some bad paint work ,

If when you are finished with it and make sure there is an air tight seal I would not think there would be a problem at all

I remember when the reactive reducers were around( DBU system for PPG) you are right after you opened the reducer (DRR) it would only last a short while like a week or less sometimes.

 

[scapegoat]

Paint company are worried about moisture getting into the hardner . Like above keep the lid on tight and store at room temp .

 

[TAZ]

Yea, normally after sitting on a shelf that long, it turns to concrete. Surprised it didn't do that on you.
I would think it would be fine if it wasn't hardened.

 

[KevinPainter]

Yea, normally after sitting on a shelf that long, it turns to concrete.

Somewhere deep in my basement i just even found a once opened can of hardener which has been there for ~2 years, and it looks okay. Thanks to the tightly closed lid i think.
And ofcourse, if you left the lid slightly open it's bad after a couple of days.