Can the Mending cantrip affix any surface to any other surface?

Question

Mending (5e cantrip-spell) has these limits:

• that the damage must be a break or tear

• the damage cannot be any larger than 1 foot in any dimension

• the spell cannot restore lost magical properties

One (entrepreneurial) player of ours suggested that ANY two unrelated surfaces can be seamlessly bound, providing both surfaces were of materials formerly broken or torn (ibid). This spell does not specify any previous relation / connection - nor is Mending a Divination spell (this magic could not know which surface belonged where previous to a casting). In fact, this spell would not even know what was 'torn' and what wasn't - implying ANYTHING could be seamlessly welded onto virtually anything else.

We pointed out we have friends in StackExchange and he would not see the last of us / this was not over / do not rest too easily &/or comfortably.

He went on: 'even with any StackExchange requiring specific torn-relation necessity, one merely need affix unrelated parts first, with any glue - once said glue is broken one is ready for a Mending weld-meld'. Example: take two polished steel parts... add Elmer's® Wood Glue... let dry / snap connection... NOW you can set-weld these two parts perfectly with a magical Mend. (Unrelated: our DM went mildly non-linear at this proposition.)

Quick &/or Dirty Summation:
How related must two surfaces be in order to connect-affix-meld a square foot seamlessly with the Mending spell?

Answer 1

Mending doesn't create new bond; it restores a broken one

The answer by Exempt-Medic already covers the basics: Mending repairs a single break in a single object, not multiple breaks in multiple objects. However, I want to answer the part of your question about affixing two objects together by first gluing them, then breaking the joint and fixing it with Mending.

So, let's take the specific example you gave, in which you glue together 2 polished steel parts with wood glue. First of all, I'm not convinced that wood glue will even stick to a smooth polished steel surface at all, but that's a real-world question, not a D&D rules question. So for the sake of argument, let's assume wood glue can weakly affix 2 steel surfaces to each other.

So, you create your combined object: 2 steel pieces glued together by a very weak joint of wood glue between them. Now, you break the 2 steel pieces apart at this weak joint, and then you cast Mending to put them back together again. What do you get? Well, here's what Mending actually does:

As long as the break or tear is no larger than 1 foot in any dimension, you mend it, leaving no trace of the former damage.

In other words, you undo the damage that caused the break or tear, leaving you with the same object you had before it was broken apart: 2 steel pieces glued together by a very weak joint of wood glue. You definitely don't get 2 steel pieces magically welded together, unless that's what you started with.

Mending is a limited "undo button"

Here's another way to think about it: Mending is like an undo button. It can revert an object to a previous state, provided that the object's current state differs from that previous state in a specific way (i.e. the difference must be a single small break or tear). Mending can never put an object in a new state that it hasn't been in before, such as creating a welded steel object from 2 steel pieces affixed with wood glue.

So yes, in a certain sense, Mending really does "know" whether or not the two pieces you're trying to join back together were originally part of the same object, because it is only capable of joining them back together if they really are pieces of the same object. Just like how Hold Person "knows" what is and isn't a humanoid, in the sense that it only works on humanoid targets. In both cases, the spell doesn't really know the difference; it just fails when you cast it on an invalid target.

Answer 2

It cannot attach arbitrary objects to each other

The mending spell states:

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

All of the examples given are clearly not separate objects but parts of a single object that broke. These are all things that combine into a single object which is supported by the spell requiring you to target "an object" and not any number of objects.

Furthermore, as user Ryan Thompson points out the spell repairs a single break or tear. If you were attaching two objects you would not be restoring a single break/tear but instead either two breaks or simply none at all.

Ultimately the way this spell works will be up to your GM but having it attach any two given objects to each other is clearly outside of the scope of the spell.

Answer 3

As an addendum to the other excellent answers (which come down to "Hah, no."), I wanted to specifically go into the suggested edge case in the question where two things are haphazardly attached together with the intent for that to break and then cast Mending:

Mending a sloppy connection that was broken will give the same sloppy connection again.

Mending restores something to a state it previously had, it doesn't improve upon that. Stapling two swords together and then casting Mending on it when they fall apart will just slap the staple back, it won't magically fuse the swords together (because they never were).

So even if your player makes an excellent case for two things having been sufficiently connected for Mending to work, it will never create a better connection than the one they had.