In our 100-year-old co-op building in NYC, I'm replacing a failed door stop with a heavier one to prevent our (very) hefty entrance door from smashing the doorway's marble.
The door stop is intended to be bolted into the floor with a sleeve anchor very similar to this one and a 5/8" pre-drilled hole.
Unfortunately, as I drilled through the tile/concrete with a hammer drill, I discovered that the floor only extends maybe 2" down, after which it seems to be loose fill/sand. If I try to use the sleeve anchor in this hole, it looks like the "expansion" part of the sleeve will be expanding into thin air, or at best only partially in the concrete floor.
What should I do? I'm considering somehow inserting as much concrete as possible into the hole, letting it cure, then drilling and continuing as before. Unfortunately I only have this 5/8" hole for access and I'm not experienced with concrete—I'm not sure if it will be thin enough for me to get enough down there before it sets.
Clarification: this is the ground floor entry way from the street, elevated maybe 3-4’ from ground level and accessed by four steps from the sidewalk.
I guess this isn’t “the” slab of the building, but just something odd used for the entry way floor. There is no access underneath the floor.
And as to the oddness of the whole thing, hey, 1913 construction in NYC? Not sure.