1920's concrete

I grew up in and my parents still live in a 17 storey reinforced concrete building in Manhattan which was built in the 1920's.

A few years when we were doing some work on a radiator, the plaster was chipped off the wall, exposing the concrete below it. I touched the concrete, and it flaked off, as if it were VERY SOFT sandstone.

This made me nervous at the time, and now that I live in San Francisco, I feel even more nervous.

Is it possible that this building could collapse on its own (there are dozens of other such buildings along West End Avenue in NYC and elsewhere)?

What about if there is a small earthquake there?

Should it be inspected somehow? And what if it is found to be unsafe? Would there be any repairs possible, or would it have to be torn down?

Thanks a lot!

RL
 

New York City
The situation you describe could mean different things, depending on the location and extent of the "flaking".

If the flaking and softening was of a structural element (beam or column) this could be a very serious problem - even without earthquakes.  If, on the other hand, this is some type of filler material (between structural elements) this could be harmless.

I suggest you contact the building department and describe the problem to one of their engineers.  Since this is a "life and safety" issue they should attend to it.

A problem with these old houses is that there are usually no plans or records left - making the analysis more complicated and less reliable.  The building department should know better than anybody else how to deal with these houses. 

If they do not help, you may wish to consult a local structural engineer. 

Another resource you may be able to use is a local University with a Civil Engineering program.  From my experience, any chance to investigate such old concrete in service is a welcome opportunity to research engineers who specialize in concrete.

As for repairs, I doubt that it will be possible.  This house was built long before existing building codes were in effect and will have to be brought up to current codes as part of extensive repairs.  Unless it is one of the "historic" buildings that are protected from demolition - the cost may be much more than the cost of tearing it down and building a new modern structure.

Regardless, I believe you should do something.  It is possible that old concrete deteriorated to the level you describe, creating a serious hazard.