I haven\'t had much success using Simple Green to get older paint off. I\'ve let stuff soak for three weeks with and it barely touched the primer. It works great on paint less than a week old and at the end of a painting session I spray it all over my plastic pallet and let it soak for a few minutes. It comes out looking brand new. Recently I started using it on my brushes. It works great but I wonder if it could be doing any long term damage to them. Does anyone else here use it to clean thier brushes?