I d use at least a foot of cement board to be safe if you can t find the spec.
Using cement board for fireplace surround.
Note that you can use thunderbolts instead of adhesive and we often do if the walls are flat and true.
Before the tile can be placed cement board must be installed.
Once i figured out to add cement board to the fireplace surround i was a little worried about the edges of the cement board showing when it was installed.
An old fireplace can be an eyesore.
Homes with outdated brick fireplaces can be brought up to date with a new tile fireplace surround.
The cement board creates a sturdy surface for the tile installation.
Fire ratings the hardiebacker board is made with a quarter inch thickness so that it can serve as fireplace facing.
Expanded metal mesh two coat stucco over top scratch and finish use play sand or another fine sand for a better finish and then prime paint.
Cement board on the fireplace surround.
However using fiber cement board like hardieboard is acceptable in locations including the mantel and fireplace surround.
I also like the stucco idea.
Fireplace surround plywood or durock cement board.
The fireplace manual should specify how far around it you need fire resistent typically cement board or steel board typically it is only for the top.
Achieving a paintable fireplace surround with cement board if paul says hardiebacker then i d trust him.
It can be used as part of a hour long fire wall which is a wall that can resist a fire for up to an hour.