How was this old floor built

[rhornung]

The owner of this vacant building in the pictures is trying to decide whether or not to rehab the property. I've been developing a scope of work for him. 2/3 of the house sits on a brick basement (most houses in the area are 1910s-1920s). The front third sits on a crawlspace of sorts. In between the each of the floor joists is concrete around 2 inches thick. Now much of the concrete is falling down. What did they do and why? The floor has soft spots throughout and will have to be torn up, I'm just trying to get an idea how bad it will be when it's torn up. Sorry the pictures are so bad, I wasn't about to try to crawl through any closer. Thanks for any ideas!

[Dale Duffy]

The floor has soft spots throughout and will have to be torn up, I'm just trying to get an idea how bad it will be when it's torn up.

I'm a pessimist, but guessing, it will be bad.....

[Barry Adair]

sounds like a failed mortar bed that was applied for tile or other hard coat surfacing...

if joists are intact, remove all loose/damaged material/debris and reframe for flooring of choice, unless other structural issues were observed that weren't disclosed in op

[Jeffrey R. Jonas]

Is that fire damage in pic's two and three?

[rhornung]

Jeffrey, the boards in question are the only ones throughout that show any signs of fire damage. And only the bracing pieces appear burnt.

Barry, all subfloor will be removed. There are other issues, but that's just the nature of the project.

Thanks guys.

[Bruce A. King]

That building was built over top of some old crawlspace foundation.
They poured concrete on it to cover up the old part.
Once all that mess is removed it should be easy to proceed assuming the rest of the building is ok.

[Jeffery L. Haynes]

Its best to simply get up with an engineer.... I am working on a 100+ year old home of which on the surface one would simply want to tear the foundation down and start over however after the speaking with an engineer we can correct the foundation at 1/4 of the price that we had budgeted. I will have a soil compaction test performed to ensure we have 2000 psf for the new footings....still the cost of it all is cheap.