I am looking at adding an additional wood insert, this one on my first floor. The house is a 50s ranch with a very small custom brick fireplace. Out of the small inserts on the market, my wife likes the Avalon Perfect Fit Plus. Link The problem is on the corner of my firebox the firebrick makes the spacing too tight. The salesman said I could remove the firebrick and replace them with a specialty fireplace approved mortar/coating . Does anyone have experience with this type of material or know what it is called? Any input would be appreciated.