If your facing will go on an uneven surface or if you simply need to raise your hearth by one-half inch, we recommend you use CV230 Micore 300 Board under the hearth.  It is a lightweight and dense fiber board that can act as a 'cushion' between the bottom of your stone hearth and the surface below it.  Micore board is 20 x 72 x 1/2" and can be cut to size easily with a utility knife.  Note:  The Micore Board will be cut into three or four pieces to allow it to be put into a smaller box if it is ordered without a set of marble, granite or slate stone facing.  If your board is cut into pieces, they can be laid edge to edge.  MSDS

Also, be sure to view our special natural stone adhesive F26 designed especially for use with masonry products.  It won't bleed through the stone.