When you rub your hand over the surface of an exterior wall and powder from paint comes off on your hand, it is probably time to paint. This is called oxidization and as paint ages, it will be a victim of the natural process. After all, with nothing but fresh air outside, it's inevitable. Home owners and property owners always ask ‘when is it time to paint my exterior surfaces’? So, now that we know the paint’s oxidization conditions are sending a message to paint, when is it a good time to paint?