Riviera Gray is a marble that needs nothing else to create a statement piece. The blue-gray background has striking white veins with occasional red threads.
Castelli puts a Resin backing on some of their stones to reinforce/strengthen it during processing, shipping, and install.
This Resin backing requires the use of an Epoxy Thinset or Epoxy Additive during installation
Common stones that will have this are Nero St. Gabriel, Rosewood, Calacatta, Statuary, etc.