In many places in the United States, masonry buildings built through 1900 and as late at the 1930s were built with a lime based mortar and not a Portland cement based mortar, which is used almost exclusively now.
There were many variations on the tradition of lime mortar but generally, the masons knew what they were doing and they mixed a mortar in a 1:3 ration of lime to sand. A mix that was softer than the masonry units and one that was intended to make sure the building would last 350 years or more.
Basic Steps to Repointing:
- Remove mortar to a depth of twice the height of the joint.
- Square the back of the joint.
- Vacuum all dust from the joint and flush with water.
- Initially, over pack the joint with new mortar and then tool as desired.