If the building or structure in question was built before 1920 you can almost guarantee it was built with lime mortar and even then most buildings were still being constructed from lime mortar right up to the end of the 1940’s.
The importance of using lime mortar to restore and repair any building constructed from lime is essential
If a cementitious mortar is used then not only does your contracted builder display complete ignorance regarding masonry restoration, the whole process is a complete waste of both your time and money, proving vastly expensive in time to come. To explain this in simple terms, lime mortar is designed to hold the brick and stone apart forming a cushion between each separate building material, this allows for any movement within the structure and therefore giving the building a longer life. Cement, however, is designed to stick each unit firmly together. All it can do is fracture and crack, creating an opening for damp. All buildings will move, even if only slightly, so when a building is restored correctly, both the building and the re-pointing will move in harmony with each other. Whereas cement has no give and will crack and separate and quite simply fall out from the joints.
There is no reason why cement should be used instead of lime as the costs are similar. Any restoration contractor will tell you their love for lime, “it just needs a little nursing when using it” a craft which sadly has been forgotten since the widespread use of cement.