Fireplace recess liner

[MFDOOM138]

Hi all,
I'm looking to line the recess in my fireplace with heat resistant board, likely to tile at a later date. The walls in the fireplace recess are quite uneven, whats the best way to get them even ready for the board to go on, or can they be left if the board is going in anyway, perhaps dot and dab some render in places to "bulk" out recesses in the brick?

Not sure on the best approach.

Thanks

 

[Tigercubrider]

Presumably this is just decorative and not a functioning fireback?

 

[MFDOOM138]

Yeah purely decorative.