Hardness applies to all spells, including acid and sonic ones. However, acid and sonic (and force -- even though it's not an energy type) are not divided by 2/4 before applying the hardness. Reread below, observing the parallel structure I highlight below (emphasis added):
- Energy Attacks
- Electricity and fire attacks deal half damage to most objects; divide the damage dealt by 2 before applying the hardness.
- Cold attacks deal one-quarter damage to most objects; divide the damage dealt by 4 before applying the hardness.
- Acid and sonic attacks deal damage to most objects just as they do to creatures; roll damage and apply it [THE HARDNESS] normally after a successful hit.
Only two spells (not powers, didn't look at them) in the SRD ignore hardness -- earthquake (against buildings) and Sympathetic Vibration (Bard 6). SpC's Crumble spell is another one that says it explicitly ignores hardness. So, unless a spell says otherwise, it is subject to hardness. --Mqs 03:15, 18 January 2010 (UTC)
- Ignore hardness: Ironguard, Rust Ray
- Do not: Shatter
- Special case: Rusting Grasp.