But what about a spell that welds the door shut permanently? The spell itself is evocative, it's not lasting more than a second or two.
You've probably never welded anything. It is going to take a lot longer than two seconds to weld a door shut so that it will withstand more than someone kicking it down. Once you conjure up energy with evocation, your part is done, and the energy just does what it does. If you want to control it better, that's what thaumaturgy is for. Or you could conjure up a magical welding torch as an evocation maneuver and tag it on a regular craftsmanship check. But if you want to do it magic only, thaumaturgy is your friend.
But, since it's altering the physical structure of the setting (melting a door shut), it's going to be a permanent change. The door won't un-weld itself after the evocation ends anymore than someone you burned to dust is going to regenerate themselves because the fireball is gone.
The door won't unweld itself, true. But depending on how you model the welding, it will be more or less difficult to crack open. For example:
- evocation block: once your magic vanishes, the seam will become bridle and give way instantly.
- "welding torch"-maneuver + craftsmanship: lasting change on the scene. Once your craftsmanship roll is beaten, your opponent managed to break the door open.
- thaumaturgy skill replacement: same as using craftsmanship, only completely magical in nature.
- evocation maneuver + might to block the door: tag the maneuver to increase your might block. As long as you press against the door and nobody beats your roll, the block is in effect.
A rule of thumb: the more power you invest into something, the better it will be. If welding the door shut is only worth an evocation maneuver to you, it will hold as good as an evocation maneuver does.
Any ideas about attacking inanimate objects though?
Really depends on the object and what/why you are doing it. Usually this is a maneuver spell, and for most things the standard 3 shifts for a maneuver will be more than enough. On a lot of things, this could even be a "mundane effect".
If you want to go for extra large things, like destroying a building and such, increase the power needed accordingly. I like to treat a lot of items like that as characters for purposes like that. A house would for example have something along the lines of hulking size + + mystic toughness + superb endurance, maybe an aspect or two to reflect its sturdy structure (or lack thereof), making the power required to "kill" it in one show quite high. Then again, an "on fire" aspect + waiting will work just as well.
If it's an object held by another person, that person should be able to defend against the maneuver. If you want to destroy the gun someone is holding against you with magic (basically disarming him), the character should get a defense roll on guns. Or athletics to dodge, or another skill, as long as it makes sense.