repairing inner hearth (floor) of brick firebox
the inner hearth (the "floor" area directly under where the logs sit) of my 1920s brick fireplace firebox had a layer of cement or mortar over the firebricks. There are some area where some mortar is missing and I can see the bricks underneath.
I'd like to repair this before making a fire - but I'd also like to do it right to reduce the chance that it will fail again. I understand that I should use fireclay mortar or refractory mortar...can I just spots patch the missing areas and feather it into the existing other mortar? Or should I lay down a new layer of mortar across the entire inner hearth?
Some spots are 1/2" to 3/4" deep...how thick can it be laid on or should I build up several thin layers?
Any other sugguestions?