George - I think that's it.
The key point of a floor like that was that it was fireproof - your link refers to lunatic asylums, as well as government buildings, which I am sure would have appealed to Ford. That (over-informative) link mentions that the concrete isn't necessarily visible, as there would usually be a wooden floor on top.
So it would be ideal for a cook-house. It would certainly fit with Valentine finding the floor "unresilient".
And girls' public schools are presumably eiusdem generis with lunatic asylums and government offices.