Do water based paints "spoil"?

[Stephen Tashiro]

Do water based paints "spoil"? I mean "spoil" in the sense of decay, not in the sense of becoming solid.

I opened an old partially used 5 gal drum of block filler yesterday and found that it had a foul oder, somewhat like spoiled milk. About a week ago, in painting class, the instructor opened an old can of acrylic based gesso and it had a similar smell.

[Lee Schierer]

Yes over time they break down and go bad. They also go bad if they are frozen at any point.