Cochran's Expertise: Working With LIME MORTAR
If your house or building was built before 1900, chances are it was constructed with lime mortar. Lime has a long and proven history. We are not really sure of its origins, but we do know the Greeks, Romans, and people of the Far East all used lime mortar extensively.
Lime is made by heating a calcium carbonate to approximately 900 degrees. This process drives off the carbon dioxide, leaving lump lime after the burn. Exposing the lump lime to water—slaking— produces the lime putty. The best limes are aged for many months, or even years, until they are ready to use.
This entire process remained completely unchanged until the 1860s with the advent of Portland cement. In the United States, Portland cement went into production in the 1870s. Premixed mortars became available in the 1930s, making modern mortar easy to use and available to everyone. In 65 years, therefore, some 4,000 years of proven technology was lost.
The lime mortar renaissance began in the 1970s in the United Kingdom, moved to Canada in the 1980s, and drifted down to the United States in the 1990s. As soon as workshops were available, Cochran’s Stone Masonry became involved. Books, seminars, and expert advice are all tools we have used to advance our knowledge of lime mortar. Today we have our own lime kiln and produce our own high calcium lime putty, which we use on all of our restoration and preservation projects.
To learn more about lime mortar, we recommend Masonry–Respectful Rehabilitation of Masonry: How to Care for Historic Brick and Stone published by the National Trust for Historic Preservation.