I do not know the science of it but have encountered in past specs for
waterproofing with "ironite" which is a stucco with iron filings commonly
used for negative waterproofing. Once had the opportunity to play with the
stuff in an electrical pit. Very tuff doodee. Worked where other solutions
did not. Not to be used for repointing of historic brickwork. A floor made of
the stuff would be very difficult to core. Beside hardness the stuff usually
will have a speckled, or dark appearance if left bare, that is, unpainted.

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