I think my biggest problem with smashing rules, is that you can sit there all day and smash stones with your axe, sword, or even fists and not damage your weapon at all.
I made this rather simplistic (in my opinion) rule. When you hit an object, any damage reduced by hardness is sent back to the weapon hitting it. The returned damage is only affected by half the weapon's hardness and is not returned a second time. For this purpose, a monk can treat his fists as iron at 7th level, and adamantine at 16th level.
It makes sundering a bit more complicated, but brings a lot of verisimilitude. Since sundering shouldn't be happening all the time, this shouldn't be a huge issue.
Makes sense to me. I almost never have players trying to break objects, so I've never had to think much about it.
Greetings,
It's really a nice idea. And, honestly, not so hard to use it (will not make the game slow down).