Need help! This fireplace is over 100 yrs old. The mortar while stable is crumbly. I’ve replaced 2 bricks (the 2 dark ones in the center) and repointed some of the mortar. I’ve shown a side angle to give you a view of how uneven the brick is. We are going to put a Jotul Oslo wood stove in front of this. We need the whole width (54”) and about 48” up for no combustible clearance. We want to tile the brick. I initially thought I could just smooth the surface with mortar or concrete, but it will just slide off. Installing metal lathe to put concrete then the tile on is out of the question, the mortar would not hold the screws. My next thought was to frame out the opening and put cement backer board over that, then I’ll have a smooth surface for tile. The wood you see is structural, except for the 2x4s set in the fireplace opening. Those are wedged in while I replaced the bricks, they will come out. My question is about non combustible clearance. Is cement board over wood studs, non combustible? Is there such a thing as metal studs?