Dispel doesn't seem like it should work to me somehow....AMF perhaps, at a discount for only extending like an inch from the wall.
Ooh, ooh! Walls of 24 karat gold that are as strong as steel! You can't take the treasure out of the dungeon because the treasure is the dungeon!!!One minor annoyance is that, per the DMG, chalk is as hard as granite and balsa wood is as strong as ebony. Never mind that the soft ones can be worked with a butter knife while the hard ones need hammer and chisel.