I have a question regarding C4

I tried using C4 on a metal door dead center and it did not blow it up. Should it be placed higher than the middle. Does it take two of them? Sorry they are hard to make and come by so do not want to waste another one.

Requires 2 C4 sometimes 3 if the door is fresh.

Thanks a ton

In a somewhat unrelated question is it possible to stop things from decaying or is it just a fact of the game.

On things that decay, such as Spiked walls, you need to equip some wood into your toolbelt and face the object you need to repair, then use the wood. If the item is made of metal, use metal fragments.

Anything attached to a foundation directly or indirectly won’t decay at all for a couple of days after being placed (as opposed to unattached stuff which is constantly taking damage). The decay timer is reset by manipulating a door or lighting a fireplace attached to the same structure. So as long as you log in every other day, your house should not take damage at all.

Shelters, wooden buildings, and metal buildings all decay as well. Anything that is attached/on top of foundations all counts as one building and it will all decay at roughly the same rate.
Wood shelters begin decaying after 12 hrs.
Wood buildings begin decaying after 24 hrs.
Metal buildings begin decaying after 4 days.
You can reset the decay timer by opening/closing a door or lighting a campfire. As long as the door/campfire is a part of the building it will reset the timer for everything attached, including things like spike walls as long as they are on top of a foundation/ceiling that is attached to the rest of the building.
When the decay timer hits zero, things will begin taking damage until they are destroyed. Things will decay from the top down.