One interesting thing that I found out, having renovated a loft in a brick building from the early 1900s, is that modern mortar is much more friable and shorter

One interesting thing that I found out, having renovated a loft in a brick building from the early 1900s, is that modern mortar is much more friable and shorter-lived than older mortars (specifically, European recipes) made with a higher proportion of lime. The old mortars flex more effectively, while moderns compounds crack and spall. When we repointed our building, we found an English stonemason with a background in historical buildings (it's not cheap, architecture). He had worked on renovating Roman-era buildings in Bath, where they found that mortar laid down thousands of years ago had survived completely intact, requiring often very minor repairs. It's sobering to think that Roman building technologies will outlast those of our own age.