Problem with Johno Water Based Undercoat

[randers]

I opened a tin of Jo Water Based U/c after about 6 months and it's separated into some solid-ish pigment and no doubt other magic ingredients and some thin watery stuff. Have stirred....and stirred....and stirred....and now it's thicker but still with too many tiny lumps in to use.
Anyone had this before or suggest how to get it usable again, or is it impossible & it'll need to be chucked? Thanks for your help.
I guess the storage might not've helped - the cupboard it's in got pretty warm!
Cheers - I do appreciate you guys' help!

 

[opps]

You could spoon it through a plastic sieve but given how cheap the paint is you might find it more cost effective to bin the tin.

 

[JohnD]

You can get a paint-stirring tool, like a propellor on a rod, that goes into an electric drill. I'd be willing to do that if I was doing a fence or shed, but not for decorating the house.

Maybe air got at it, or maybe it froze in winter.