I recently renovated the fireplace.  It had red brick around it and a red brick hearth and old broken brass doors.  In my excitement and haste I failed to take any before pictures.   Removed the hearth and then I finished the grade with leveling cement (love that stuff).  I chose to put bedding sand under the marble instead of thin set.  Hopefully that will help prevent expand and contract fissures, etc.  I got the new black door on craigslist.