Does hardner get old?

[Unruh]

I'm planning to paint a fender with Omni MAE and use Shopline JC661 clear over it using JH6680 Medium Topcoat hardner. I read in a thread by NCWaye in Tractor Talk that he refers to hardner that might be "out of date". I used half of my can of harder maybe three years ago and refilled the can with argon gas before screwing on the cap. How can I tell if it's still good or not good? Spray a test on an old barrel? The clear will never harden without hardner, will it? I don't see a "use before" date on the can.
 

[CNKS]

I have used it a year old with gas in it and kept in the refrigerator without problems. My guess would be that it is still ok, but if mine I wouldn't risk it. I don't remember the numbers, but I think PPG says the shelf life unopened is 2 years, opened 2 weeks without gas. The 2 weeks is probably conservative, mainly there for body shops to reduce complaints, in my opinion.
 

[souNdguy]

if it was something i wanted to look good.. i'd get a new can.. 3ys opened is a loooong time..
 

[Loren in WI]

yes it has a shelf life after opening. The humidity that enters the can will cause it to not work. It is not that body shops are fussy it is that it has to have a chemical reaction to work right. I would suggest that you buy it in a small contyainer and use it up promply. 25 years of shop time sharing knowledge with you. It cost alot to do it once, what to try it twice?
 

[GordoSD]

Deep six it. As others said it cost a lot to do it right ONCE!
 

[jfred]

The PPG paint rep had told me that the way to know if it is alright to use after being opened for awhile is to take a look at the paint just after you mix the hardner in. If it starts to look in any way like cottage cheese, stop right there and throw it out before pouring it into your gun. If it mixes up like normal it will be fine. Again that's just what he told me. I have to admit, I have mixed together some PPG hardner that was probably nearing 3 years old once and it worked just like it should. But I could've just gotten lucky!