Sword Breaker Dagger

Concerning the Swordbreaker Dagger (from Advanced Player's Guide). The dagger offers +4 to Sunder and Disarm attempts. Great for disarms, but when it comes to sunders, the dagger does the same damage as a normal dagger (1d4). This means that even a character with a decently high strength (say, 20) would be hard-pressed to sunder a an enemy's blade, as blades have a hardness of 10.

However, as noted on this page:
http://www.d20pfsrd.com/equipment---final/damaging-objects

"Vulnerability to Certain Attacks

Certain attacks are especially successful against some objects. In such cases, attacks deal double their normal damage and may ignore the object's hardness."

A sunder from a Swordbreaker dagger seems like it would be one of those "certain attacks", so my question is, to what extent? Does a swordbreaker dagger do double damage against the types of weapons it was designed to break, and does it ignore such objects hardness?

It doesnt quite work that way.

First: You make a sunder attempt. Success means you do damage.

Second: Do damage. 1d4 is mostly irrelvant to this. It is your bonuses that count. Assuming a character of around level 8 that becomes: 1d4+2(magic)+6(str)+6(power attack) = 1d4+14damage. Right there you will definitely be applying at least a little bit of damage to most materials. If your weapon is adamantine then there will be no hardness to contend with.

As for Vulnerability to Certain Attacks, I do not think sunder attempts normally qualify. I think it is intended for things like 'slashing vs rope' 'bludgeoning vs glass' etc.

- Gauss