In the past I've taken some of the same limestone as needs filled, ground it to fine & course dust. Mix plenty of that with epoxy to look like stone. Add color if needed. When hardened it resembles the stone and grinds just like it. 

Does anyone have any suggestions for filling and restoring this limestone floor.  It is outside at a house that is directly on the beach.  No maintenance has been done to the stone.  Any suggestions would be appreciated.
--