History of Lime Plaster
Lime plaster has a history dating back to many Millennia. This ancient material has mostly been prepared by mixing water, various aggregates, and animal hair with lime. Its versatility, breathability, and durability have contributed to its value. Here is an overview of the history and characteristics of lime plaster and LimeWorks®.us Ecologic™ Plaster System:
Ancient Use
Lime plaster has ancient roots, with evidence of its use dating back to civilizations such as the Egyptians and Romans. Both cultures used lime plaster in various construction applications, including on walls and ceilings. Most notable in the construction of the Great Pyramids. The smooth white Tura limestone casing that once covered the pyramids was made partially of lime plaster, providing a polished and reflective surface. The Colosseum in ancient Rome featured Lime Plaster in its construction and decoration. The interior walls and architectural details featured numerous lime plaster finishes, contributing to the grandeur of the world-famous amphitheater. Both ancient Greek and Roman civilizations utilized plaster in their architecture. The Greeks used it for decorative moldings, while the Romans developed more advanced techniques, including frescoes on plaster walls.
Medieval and Renaissance Periods
Lime plaster became a prominent building material during Europe’s medieval and Renaissance periods. Grand castles, intricate cathedrals, and other iconic structures used lime plaster. The flexibility and ability to adhere to different surfaces made lime plaster a preferred choice for decorative elements. Many historic European cathedrals, such as Notre Dame Cathedral in Paris, used lime plaster in their construction and interior ornamentation. Lime plaster’s workability allowed artisans to create intricate carvings and decorative elements.
In the Americas
Across the Atlantic, people in the Americas have used lime plaster as a staple in the construction of buildings, from parging up cellar walls to rendering a shelter coat over brick, stone, adobe, and timber buildings. It has been used to unify walls, for decoration, sanitation, waterproofing, and to reflect light, absorb, and reflect sound. In Charlottesville, Virginia, Thomas Jefferson’s iconic home, Monticello, recently had many lime plaster features restored. The interior of Monticello includes lime plaster finishes on walls and ceilings, and exterior portico columns. The use of lime plaster is in keeping with the neoclassical and Palladian design principles favored by Jefferson. Located west of Monticello is the historic landmark and museum, Mission San Juan Capistrano. Founded over 200 years ago, the Mission still provides a magnificent look into California’s multicultural history. Established by Spanish Padres and Native Americans, the Mission originally served as a self-sufficient community, functioning as a hub for agriculture, industry, education, and religion. The original construction includes adobe, lime mortar, lime plaster, and lime wash that has continually been restored since the nineteenth century. These modern conservation tasks using traditional materials guarantee that future generations will continue to enjoy this significant California landmark.
Breathability and Durability
One of the key benefits of lime plaster is its breathability. Unlike modern materials like Portland cement or gypsum, lime plaster allows moisture to evaporate, preventing issues like trapped moisture and mold. This trait makes it suitable for historic buildings and restoration projects.
Contemporary Use
As interest in historic preservation grew in the late 19th and early 20th centuries, lime plaster experienced a revival in restoration projects. Preservationists recognized its compatibility with historic structures and its ability to maintain the original breathability of the walls. Lime plaster is still used in restoration and conservation projects where historic accuracy and breathability are essential. It is also appreciated for its environmentally friendly qualities, as the production of lime has a lower carbon footprint than Portland cement.
Lime plaster continues to be a valuable material for those seeking a more traditional and sustainable approach to construction and restoration. Its unique properties make it well-suited for specific applications, particularly in preserving historic buildings where maintaining the authenticity of the original construction is crucial. At LimeWorks®.us, we offer the Ecologic™ Platinum Plaster System that uses a grouping of our prepared lime products that all work together to obtain a pure lime plaster outcome. Our TAKCOAT® Platinum is a specially formulated lime plaster base coat designed for sound interior/exterior applications, primarily for original flat wall repairs. We then offer the Ecologic™ PLASTER TOPCOAT™ Platinum, a prepared blend of binder and aggregates for interior or exterior work. As with the TAKCOAT® Platinum, installers must add water, mix, and then go to work to finalize the outcome for a beautiful lime plaster system. The Ecologic™ Platinum Plaster System is appropriate for Historic and Sustainable Buildings. It is based on our ‘Made in America’ Pozzolanic Hydraulic Lime (PHL), giving it our ‘Platinum’ designation. TOPCOAT™ has various graded sands that create Coarse, Fine, or Xtra-fine finishes. The ancient tradition of using lime plaster inspires us to use only the highest quality materials, starting with 98% pure calcium carbonate (Lime!).
In comparison with Portland Cement mortar in brick construction, how resistant is lime mortar to moisture? How does moisture affect the strength of lime mortar in comparison with cement mortar (most typically used in exterior applications in modern construction)?
Hello James, thanks for your question. Portland cement mortars are much more resilient to water infiltration than lime mortars due to their higher density and smaller pore structure. However, the flip-side to this is that when water does eventually get into Portland cement mortars, the mortar tends to hold on to that moisture much longer than lime. Owing to its more plate-like microstructure, lime is less dense and has greater porosity which more readily allows vapor to exchange out of the system. Lime mortar in heavy rain will reach saturation in about four hours, while it takes Portland cement mortars almost 24 hours. However, once the sun comes out and the air heats back up, the lime will be dry within 8 hours, while Portland cement can take several days to fully dry out. Practically, since in temperate climates moisture is almost always present, this functionally means that cement mortars in many places will be perpetually damp to some degree. Modern systems designed around cement mortars tend to make use of a veneer and drainage, while older lime mortars function best in mass masonry walls where the mortar joints are essentially the drying surface for the wall.
In general, lime mortars are more flexible and weaker than cement mortars. If you put both kinds of mortar under constantly flowing water, lime would likely breakdown first, but in the real world where vapor and freeze-thaw are more likely than perpetually flowing water on a masonry wall, cement tends to run into problems from dissolved minerals (salts) or atmospheric deposits (sulfates) before lime will. Technically, cement keeps its strength longer than lime, but it also tends to experience deterioration that can cause damage to the surrounding masonry that is less common in lime. Cement mortars also tend to be overly strong in bond on historic masonry which can lead to damage to the masonry units and difficulty when repointing becomes necessary. It’s important to remember that in mass masonry structures, the mortar needs to be sacrificial, meaning less dense and more vapor permeable than the surrounding masonry. I’d argue that when considering a historic wall, compressive strength is probably not the primary property you should focus on. Instead, density, permeability, and bond should be regarded first. For specifying historic mortars, refer to ASTM C1713 instead of C270 especially for buildings over about 60 years old that are mass masonry.