Could 'Tenser's Floating Disk' be used to block a door?

Question

The spell says it is immobile while within 20ft of the caster. I'm also assuming that since the items it's holding can't pass through the disk, a door couldn't either... I'm wondering if it could keep a door from being pulled out with a setup like this (disk) -| (door) where the disk is horizontal, but preventing the door from being pulled open.

Here is the spell readout:

This spell creates a circular, horizontal plane of force, 3 feet in diameter and 1 inch thick, that floats 3 feet above the ground in an unoccupied space of your choice that you can see within range. The disk remains for the duration, and can hold up to 500 pounds. If more weight is placed on it, the spell ends, and everything on the disk falls to the ground.

The disk is immobile while you are within 20 feet of it. If you move more than 20 feet away from it, the disk follows you so that it remains within 20 feet of you. It can move across uneven terrain, up or down stairs, slopes and the like, but it can’t cross an elevation change of 10 feet or more. For example, the disk can’t move across a 10-foot-deep pit, nor could it leave such a pit if it was created at the bottom.

If you move more than 100 feet from the disk (typically because it can’t move around an obstacle to follow you), the spell ends.

Let me know what you think!

Answer 1

Tricky, but I'd say yes

D&D 5E rules are supposed to follow the exact wording including definitions of words. Immobile, as defined here, includes this text:

not moving, or not able to move or be moved:

In that case, the floating disc can't be moved by someone pushing on the door so it could be used as a door blocker.

I will note that the example for the above definition is a bit dicey since the example given is:

He is in a cast to keep his spine immobile.

This isn't so much a case of literally being immovable but rather that it would be a bad thing to have happen.

I will also note that the spell description doesn't cover details about the disc being moved by outside forces. It does mention that it can't handle over 500 pounds of weight, but that is more to do with vertical load rather than horizontal force.

Answer 2

Yes(?), but...

The rules do not directly cover this so it would be a DM ruling. That said, the spell does cover force applied vertically.

The disk remains for the duration, and can hold up to 500 pounds. If more weight is placed on it, the spell ends, and everything on the disk falls to the ground.

So a DM could apply the same rule to horizontal forces on the disc. If more than 500 lbs of force is applied on the blocked door, the disc goes away.

Note that, unless you have a Large creature or a battering ram, it would probably be easier to destroy the door rather than trying to apply 500 lbs of horizontal force.

Answer 3

If you take the spell's text, you'll find these two passages:

The disk remains for the duration, and can hold up to 500 pounds. If more weight is placed on it, the spell ends, and everything on the disk falls to the ground.

and

The disk is immobile while you are within 20 feet of it

There are a few ways you could interpret this. As a DM, I might note that 500 pounds is a measurement of force. Therefore, Tensor's Floating Disc can withstand up to 500 pounds of force, and if more than 500 pounds of force is applied to it, the spell fails. So if you were have it block a door, it would work unless the door had 500 pounds or more of force applied to it, in which case the spell would fail and the door would open.

I could also make the case that the disc simply stays immobile no matter what and blocks thing that try to move through it, which would make this spell really good at keeping things closed.

Lastly, I could say that immobile in this case means that the disc will not move of it's own impetus unless it's 20 feet away from the caster, in which case it would simply move out of the way of the door.

Answer 4

No. Spells do what they say they do.

In general, in 5e, spells do what they say they do, and no more. Tenser's Floating Disc doesn't say anything about blocking objects from moving through it in a horizontal direction, so it doesn't; the only way it interacts with objects or creatures is to carry up to 500 pounds of them. It can't push things or pull things; it can only carry them. It doesn't seem to be able to move through solid objects (since its movement is blocked by a pit wall), but it also doesn't take up a space on the combat grid, so creatures and things like doors can freely move through a space it occupies.