4e DMG p 66:
Usually, it doesn’t matter what kind of attack you make against an object: Damage is damage. However, there
are a few exceptions.
All objects are immune to poison damage, psychic damage, and necrotic damage.
Objects don’t have a Will defense and are immune to attacks that target Will defense.
Some unusual materials might be particularly resistant to some or all kinds of damage. In addition, you might rule that some kinds of damage are particularly effective against certain objects and grant the object vulnerability to that damage type. For example, a gauzy curtain or a pile of dry papers might have vulnerability 5 to fire because any spark is likely to destroy it.
4e DMG pp 73-75:
When a player’s turn comes up in a skill challenge, let that player’s character use any skill the player wants. As long as the player or you can come up with a way to let this . . . skill play a part in the challenge, go for it. . . . Always keep in mind that players can and will come up with ways to use skills you do not expect. . . .
Sometimes, a player tells you, “I want to make a Diplomacy check to convince the duke that helping us is in his best interest.” That’s great—the player has told you what she’s doing and what skill she’s using to do it. Other times, a player will say, “I want to make a Diplomacy check.” In such a case, prompt the player to give more information about how the character is using that skill. Sometimes, characters do the opposite: “I want to scare the duke into helping us.” It’s up to you, then, to decide which skill the character is using and call for the appropriate check. . . .
In skill challenges, players will come up with uses for skills that you didn’t expect to play a role. Try not to say no. . . . This encourages players to think about the challenge in more depth and engages more players by making more skills useful.
However, it’s particularly important to make sure these checks are grounded in actions that make sense in the adventure and the situation. If a player asks, “Can I use Diplomacy?” you should ask what exactly the character might be doing to help the party survive in the uninhabited sandy wastes by using that skill. Don’t say no too often, but don’t say yes if it doesn’t make sense in the context of the challenge.
The following two propositions are not the same:
*The GM is discouraged from using pre-conceived fiction to shut down mechanically permissible action declarations;
*The fiction doesn't matter.