If you look at the sunder rules, they only talk about weapons. That would imply sunder only works when talking about weapons- which is a big deal when talking about improved sunder.
However, if you look at teh shatter spell, the spell "sunders" a single nonmagical object. This object is not necessarily a weapon.
However, if you look at teh shatter spell, the spell "sunders" a single nonmagical object. This object is not necessarily a weapon.