..just as info. I currently have a can of POR15 that has been open for quite sometime (months) and I still use it ocassionally.
A fellow bolter, I forgot who, suggested drilling a hole in the top of the lid and pour out what you want to work with then tape it up with duct tape. I have done this quite a few times and its till good. I usually put a new piece of tape back over the hole and shake it a time or two. Just make sure the lid is clean and you rub the tape on real good.
I like this method as it will "skim" fairly quick if not careful. So, I pour out a little at a time so as not to waste it.
oh, I drilled a 1/4" hole in the center of the lid.
Hopefully this will help someone preserve what they don't use up.
Thought I'd add my 2 cents. Achipmunk is right. It will skim over and the skim is hard to crack to get to the remainder underneath.
I read somewhere that you can pour the POR-15 out into individual plastic bottles, like single serving 16oz. water bottles. They must by ABSOLUTELY DRY before filling. Anyway, you just pour from the bottles as much as you need and then gently squeeze the bottle to remove the air and reseal with the cap. It keeps the POR-15 from skimming and saves the mess from pouring from the can each time. A small piece of plastic food wrap makes the cap seal tighter too.
