Earthfast

(Spell Compendium, page 76, DnD 3.5)

Transmutation

Level: ; Druid 2
Components: V, S
Casting Time: 1 standard action
Range: Close (25 ft. + 5 ft./2 levels)
Area: One stone structure or rock formation, up to 25 cubic ft./level
Duration: Instantaneous
Saving Throw: None
Spell Resistance: Yes (object)

Gray bands extend from your fingertips, wrapping themselves around the wall like a brace strengthening it for the coming assault.

You reinforce a rock formation or stone structure. The earthfast spell doubles the structure's hit points and increases its hardness to 10. This spell does not function on constructs.