I've owned my current home for (4) years and had the fireplace cleaned last year. The home was built in 1987 and I believe this is all original. I've yet to use the fireplace. Recently, while installing a chain screen some of the mortar or cement fell out between the exterior brick veneer and the steel firebox. What would a professional use to fix this? Should I chip it all away and replace the the entire joint?? Thanks in advance!