Winter, our old friend, comes every year. A time to reflect on 2019 and plan for the upcoming year. Over the past few decades Americans have begun to care much more for the historic structures around them. I can think of many cities where there were crumbling old areas that are now prime real estate due in no small part to the preservation and conservation of the historic fabric of those places. But I have also seen far too many buildings where it would have been better if nothing had ever been done to them. An ill informed repoint can destroy an old masonry building. It happens every day.
My job is to inform that the materials and processes used to make mortars and grouts in the past, and even masonry units themselves, were far different from those today. In general historic masonry is much softer and or porous. The difference in hardness between historic brick and mortar, and today’s brick and mortar is great. Historic brick is generally much softer and its lime based mortars are not only softer but also flexible over time, thus the masonry wall was in balance, wetting and drying and moving together over time. New masonry and its mortars are much harder. The masonry envelope of today’s buildings is very different from a century ago. The mortars are harder and much less if even flexible. So if a historic building is repointed with today’s out of the bag mortar, the softer historic masonry units will be the path for moisture. Its simple physics. The movement of moisture through masonry units instead of mortar joints creates a cascade of ill effects ending with spalling, cracking, mortar failure and structural failure.
Analysis of the unique characteristics and properties of your historic masonry structure is critical to matching materials in repair and conservation of its masonry units and joints.
Now is a good time to look at masonry and discuss goals and objectives in its care. As precipitation and freezing occur, observation of wetting and drying in these conditions can tell a lot about the particular dynamics of your historic structure.
As you look at your old masonry, try to get a sense of the relative hardness of both the masonry units and their mortar. If there are problem areas, can you see a difference between the mortar in those areas and the original? Restoration masons would concur that the vast majority of problems in historic masonry have been caused and still are caused by a repoint using the wrong mortar. But with some thoughtful observation and assessment, these issues can be remedied and an appropriate maintenance schedule created using appropriate materials and technologies.
Sometimes, an old mason reaches out from a century ago and hands you a note. One day while I was driving in southern, New Hampshire, I stopped at a library to look at its beautiful and nearly pristine masonry. As I discussed the building with the librarian she indicated that the original mortar formula had been written down and was still used a century later to maintain the joints.
What a great way to end this chapter!