Since introducing decay it’s a requirement to run around bashing your own base with a hammer even if it’s made of reinforced armor and you’ve been active inside it the whole time. I’ll leave my thoughts on that for another time…
Because you need whack stuff with the hammer, it means that any part of your building obscured by another part, or a floor with a sleeping bag and boxes all around it, cannot be repaired. The hammer just pointlessly hits the sleeping bag or boxes and your foundation slowly decays.
Can this be fixed? If a part of a building is going to decay and need to be hit with a hammer, then it really needs to be possible to hit it with a hammer without having to leave space on each square to do so.
The simple answer would be to have the hammer go “through” anything that it doesn’t have an effect on - like boxes and sleeping bags. Or to put it in the right click menu to repair with the hammer… or to repair all parts of a building from a toolbox, or something. Lots of people are finding that they have parts of their base that are unreachable to hit with a hammer and therefore will eventually cause parts of their base to fall down.