How does Mending interact with corroded weapons?

Question

The Black Pudding's Corrosive Form contains the following text:

Any nonmagical weapon made of metal or wood that hits the pudding corrodes. After dealing damage, the weapon takes a permanent and cumulative -1 penalty to damage rolls. If its penalty drops to -5, the weapon is destroyed.

The Mending cantrip is as follows:

This spell repairs a single break or tear in an object you touch, such as a broken key, a torn cloak, or a leaking wineskin. As long as the break or tear is no longer than 1 foot in any dimension, you mend it, leaving no trace of the former damage.

So a few interconnected questions culminating in how does Mending interact with corroded weapons:

• Since corrosion represents material that is worn away, not a break or tear, does Mending technically even work on it?
• Would Mending mitigate the permanent and cumulative -1 penalties to damage rolls?
• Since mending heals a single break or tear, does it work on multiple consecutive breaks or tears if used back-to-back-to-back-to-back?

Answer 1

RAW, No, Mending cannot remove corrosion.

As written, the spell repairs things by joining together parts that have been separated. There are four specific samples given, and none of them change the properties of the material in any way. Corrosion represents a change in the substance of an item. It could no more remove corrosion than it could turn cheese back into milk, or bad food back into good.

To answer your other questions, no. Mending would not remove the penalties that come from corrosion. These represent fatigue and weakening of the object, not a break or tear.

As for the last part, I would say that yes, multiple usages could rejoin an object that is in more than two pieces. You are joining two parts with each application. A DM would probably be within his rights to judge that the damage of a small object broken into many piece is just too damaged for the spell to work.