rmh riser material

Thank you for this information.  I understand the different kinds of fire brick.  I have a question is ceramic fiber wool the same things as mineral wool?  Also is ceramic fiber board the same as "Micor"  a mineral wool board used in making hearth pads?

Hi Kathy;
I'm sorry!
Somehow your post slipped past my radar!

No, ceramic fiber blanket is very different from "Rockwool".
The preferred ceramic blanket is called Morgan  Superwool.
As it is sold, it is non-biohazard. Safe to handle, non itchy.
After heating over 1200F it is not as safe as new and common safety precautions (face mask) should be followed.

Rock wool has been used many times in RMH Construction.
However, it is not rated for as high temperatures as Superwool is (2300F)
It is extremely itchy stuff to work with a mask, gloves, and long sleeves are a must.
Not many builders use it much at all anymore.

I have not heard of "Micor."
  If you were hoping to use it in an rmh core or riser it must be good to a minimum of 1800F