New St. Laurent, is a marble with variations of brown threadlike veining. A polished finish gives life to the veins and a distinctive and elegant appearance.
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.