What would cause latex paint to thicken up? I had a can of SW proclassic that thickened up. I had been using it for a several projects (trim, doors, etc) arround the house for the last year. The last 2 projects it seemed thicker than normal and was very difficult to work with. I purchased a new can and was suprised how much the consistency changed. The only thing I know for sure is that it did not freeze. Also, when I cleaned the old can out there was alott of settled material on the bottom. Would it have returned to the original consistency had I mixed it better?