I have uncovered a large red sandstone fireplace (about 2 meters wide and a meter deep). It had been infilled with a large amount of bricks and cement. The stone at the back of the hearth are in very poor condition and in places have brushed away completely, exposing the concrete harl on the outside of the house.
We are working with lime, as concrete will do more damage in the long run. I would like to build up the back of the hearth. I am looking for the best way to add strength. We have been advised lime mortar with small slate pieces can be applied to build the wall up. I would like to know if pouring a lime mortar and aggregate mix into shuttering would be an option?