What Is Lime Mortar and Why Is It Important?

It’s fun to visit historic buildings. However, you may wonder how these structures have stood the test of time. After all, given advances in technology and construction, shouldn’t these buildings be falling apart? A large part of why these buildings still stand today is lime mortar. But what is lime mortar, and why is it important? Read this guide to learn more.

What Is Lime Mortar?

Lime mortar is a mixture of lime, water, and aggregates like sand or gravel. People used it for centuries in ancient civilizations and still do today to cement building materials like stone or brick. Lime mortar commonly falls into two types. They are hydraulic lime (HL) and non-hydraulic natural lime (NHL). Hydraulic lime refers to a form of lime called quicklime, in which calcium oxide sets through hydration. For quicklime to become lime mortar, it must become set through carbonation in the air. Non-hydraulic lime is calcium hydroxide that undergoes a heating process to become pure calcium carbonate, drive off carbon dioxide, and produce quicklime. This process occurs in a lime kiln. Then, the people who use it slake or hydrate it (mix it with water) to create a lime putty.

What Is It Used For?

Lime mortar commonly helps preserve historic buildings that originally used a lime putty to cement brick or stone. Modern structures often don’t use lime mortar and instead use Portland cement. Still, lime mortar is an alternative to cement in some situations, as Portland cement can be too hard, inflexible, and impermeable to moisture. On the other hand, lime mortar is porous. Therefore, it can release moisture and further protects the structural integrity of the building. Lime mortar has historical uses. Ancient Egyptians, East Indians, and Colonial Americans used lime mortar to secure structures. Many colonial buildings throughout the United States have lime mortar.

Why Is It Important?

When thinking about what lime mortar is and why it’s important, you must understand that lime mortar is one of the few options for preserving historic buildings. Given its unique needs, historic building preservation must undergo specific steps to avoid causing damage. Lime mortar’s porous nature allows moisture to escape and adds structural foundation to dilapidated buildings. Both professionals and homeowners use lime mortar in their endeavors.