I tried to create a prop with the world model of a chunk of concrete lying somewhere. Therefore I chosed "Concrete_chunk02a" and afterwards "concrete_chunk08a". But the prop will not be shown neither as a dynamic nor as a static entity. The info tab says the prop can be used as static or physic. If I chose a prop_static, Hammer complains I should use a prop_dynamic. If I do so, nothing appears. I don't want the chunk to be moveable, so no prop_physics for me.
Anybody has any idea why this issue appears?

prop_physics and put it to sleep without any way of waking it up?