House foundation chimney jog.
 

I have a jog in the poured concrete foundation for my house. They are added for a fireplace which my house does not have. At some point a chimney for a stove was added on top of it. My problem is the concrete that the jog is made out of is crumbling and I'm afraid the chimney will fall. The jog sounds like it is hollow when I tap on it. My question, is it hollow and could it collapse?

Are you sure it's concrete , or is it 8'x8'x16' concrete block. If built before around mid 60's it's probably Cinder block, which would be failing somewhat

The house is new than that. I'm sure it's poured. It even has the metal rods sticking out that hold the forms in place,

Happen to have any pics?

Sorry not at this time.