2 part polyurethane - shelf life once opened?


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Established Member
4 May 2012
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I'd like to use 2 part poly but just a smallish amount at a time.

I'm wondering if the varnish still reacts with oxygen like regular varnish does.

Or will it stay fine till the part B is added even if the can has been opened and exposed to air?

The catalyst normally goes off after a while- ends up looking a bit like PU glue. I imagine the base is ok for a bit longer but most makes only sell the base/catalyst together. Cost wise it's best to buy in the smallest quantity possible and use in biggish batches- I try to open the catalyst tin as few times as possible to minimise contact with fresh air.
+1 for the above.

And I'll also add that if possible, both bottles/cans, but especially the hardener, will last a fair bit longer if kept in the fridge.

Same is true for a mixed up batch - if you've got a bit left over but might need it for touch up, put the remainder of the mixed batch in the fridge in an airtight jar (I use old jam jars). It won't last long but you should be able to do the odd bit of touch up with the original mixed batch leftovers next day latest. When removing from fridge allow some time to come back up to room temp - and please note ,fridge, not freezer (DAMHIKT)!
Thanks, I'll try and be careful with it then. Good to know the hardener goes off with air too.

This is expensive stuff so the more I can preserve the better.