For thousands of years prior to the Industrial Revolution, lime was the principal binder used in construction. Mixed with mortars, it held beams in place and was an important component in laying brick walls. Lime was used alone as a binder in paints and whitewashes. It was later combined with other minerals in Venetian Plasters and for application of expensive high-grade stuccos in palaces and churches.
Because of its durability and long life, lime was used to help strengthen many medieval structures. Ancient and Renaissance artists preferred using Lime in Frescoes because it perfectly blended with pigments that could produce brilliant colors while resisting fading.
A tour of old neighborhoods in cities like Paris, Prague and Venice offers many glimpses how of this versatile and practical product was used over the centuries in churches, hotels, banks, bridges and public squares.
Use of lime began to decline with the invention of Portland cement in 1824 and continued through the 1960's when interest in historical preservation began to increase. Architects and builders "rediscovered" Lime's interesting characteristics not just for remodeling and renovation but also for new construction in across the world.
The Historical Record: Archeologists can date buildings using samples of lime plaster found in historical sites. It has been used for 8,000 years all over the world...
- 6000 BC- First use of chalk plaster as binder in Turkish city of Konya.
- 5000 BC- First use as whitewash on Temples in Mesopotamia.
- 3000 BC- Lime used as binder mixed with sand in Pre-Colombian America. Indians burned seashells to extract lime. Egyptians used lime mortars and lime whitewash as pigment and under painting for their tomb and temple murals.
- 1900-1600 BC- Lime used for frescoes and palace walls at Knossos, Crete.
- 700 - 320 BC- Greek architects and artisans incorporate marble dust into stuccos applied over lime-based mortars at Delphi and the Acropolis in Athens. The Greeks also invented ways to mold lime in bas relief, created colored lime plasters, utilized and categorized hundreds of pigments to brighten plaster, and discovered and harnessed the waterproof properties of lime in cisterns, basements and seaports.
- 300 BC- Roman builders enhanced the Greek's knowledge of lime by improving the production process. They designed special kilns to burn the lime at higher temperatures making a very pure product; they discovered the chemical properties (carbonite reaction); and made tools to accurately and economically apply large amounts of plaster. Their writings about lime composition and building techniques are still extant as are famous examples of monuments from the Coliseum to Aqueducts and the famous frescoes of Pompeii.
- 1500's- Italian Painter Ceninno Ceninni wrote a seminal art book about stuccos, colors and an "a fresco" technique. New manufacturing techniques improved quality and discovery of "Non-hydraulic" lime (Grasello di Calce) made application and use easier. Famed Italian architect Palladio used lime plasters extensively in his buildings in Venice and Verona (the White House is a Palladian Revival building).
- 1500's - 1900's- Chemists improve lime manufacturing with new formulations. Beginning in 1850, cement factories were constructed in England and France along with the lead-lime kilns required for the cement process. Lime use declines as synthetic substances are incorporated in mortars.
The Modern Lime Plaster Finish (from an article in Artistic Stenciler, Spring 2007 by Nick Brown)
Whereas the traditional lime plaster system required months to cure out in three coast, today’s applications provide all of the beauty and function of these traditional systems with much more practical working conditions. On the interior, lime finishes can go over Level 3-5 drywall – Level 3 if you’re putting on an aggregated lime plaster. You will need Level 4 or Level 5 drywall, if you’re applying a finer lime plaster to achieve a shiny marble effect. Typically, a primer coat is needed to bridge the interface between gypsum wallboard and lime plaster. These are commonly acrylic or silicate primers with marble aggregate in them to provide for good adhesion to the substrate, a good key for the plaster finish coat, superior crack-resistance, and mold- and mildew-resistant. The finish coat is toweled on in two or three coats. This is necessary to achieve the full depth of color and mottling that only true lime products can produce.
In Exterior applications, lime products can be matched with modern materials to create an easy-to-apply, durable, attractive finish. In traditional stucco market areas such as the Southwest, lime plaster is usually applied over lath, scratch, and brown coats or Portland cement and sand. This system gives the fast completion time that builders demand from today’s materials, but still achieves the look of lime that takes yesterday’s architecture to a higher level. The brown coat should be smooth to ensure that no additional expensive lime plaster material is used to fill in a rough brown. As with interior applications, a primer coat is commonly employed to bridge the transition between Portland cement and lime. Then, two coats of lime plaster are troweled on, as with a Santa Barbara Finish stucco product. In other regions, lime plaster can be applied over properly prepared masonry or foam substrates, with a base coat of cement plaster, cement board sheathing, or other accepted cementitious substrate.
Features of Lime Plasters
Lime plasters have gained their niche in the US market because of how they look. But they have important performance advantages as well.
- Crack resistance: lime is far more flexible that Portland cement, so you can expect greatly reduced cracking.
- Very Breathable.
- Wets out and dries out FAST: this is a new way of thinking about water resistance. Whereas US manufacturers typically try to keep water out, lime plasters perform very well in wet climates (such as in Europe) by simply allowing any water that is absorbed into the plaster to quickly evaporate and exit the structure. This makes lime plasters the only plasters that can tolerate rising damp and canal-side applications that would delaminate acrylics and Portland cement plasters.
- Self-healing: during construction, when buildings are most likely to be under stress cracks, the fresh lime has been known to actually fill in small stress cracks. This may explain, in part, why lime plasters show far fewer cracks than cement plasters. In fact, ancient buildings have had lime mortar deep in walls which started to set when archaeologists exposed it.
- Naturally mold-resistant; due to its high PH (between 11 and 12), lime is a natural biocide.
- Time tested: from early Egyptian, Greek, and Roman efforts with lime through the golden age of lime in the 1800’s, lime plasters have served as durable finishes.
- Natural and green: lime plasters are sustainable materials produced without plastics and harmful chemicals in keeping with traditional plastering methods.
- Easy to patch and maintain: fresh lime plaster can be brought back with water spray for up to a week after application. This gradual setting process allows for relatively easy repairs, compared to Portland cement and especially acrylic plasters.
Additional Considerations When Using Lime
If you’re like most American construction professionals, you have heard stories of lime plasters that were casked in holes in the ground on the jobsite, and used after several months to plaster the interior. But there is a certain fear factor in bidding work using products that are new to someone, no matter how old and time-tested the product might be. Everyone new to using lime thus needs to keep the following things in mind when startling to take on lime projects.
- Added expense: authentic materials cannot be made from bag lime and so must come from Europe. Labor cost should be roughly the same as smooth Portland cement plaster finish, but materials could run an extra $10=$20 per square yard. Figure on the same applied cost as painted smooth stucco, and you’re probably in the ballpark, but your manufacturer can give you the guidance you need to bid jobs.
- Pay attention to roof and deck runoff if you don’t want that kind of stained character; gutters are a good idea and designers need to realize that water running down a lime plaster will create an old-world look that not all homeowners appreciate.
- Extended cure time means extended vulnerability to freezing, so be sure that temperatures will not drop below freezing for about one week after application.
Lime plasters have arrived in the US to support the demand for European architecture and high-end aesthetics. Their performance advantages are likely to keep them around for generations to come.
There are a lot of product offerings flooding the market these days, so be sure to ask the right questions about how their lime is produced. The real test is putting the materials on the wall and enjoying the warm, natural glow of the lime. With education and a little trial and error, lime plasters can elevate the appearance of a building and enable construction professionals to differentiate their work, recapture the tradition of artisans from generations before, and create art on the wall.
End of Excerpt from Artistic Stenciler Spring 2007.
Calcination of Limestone
Lime comes from limestone blocks, which are composed of carbonate of calcium (CaCO). The stone is crushed and burned in ovens at high temperatures of 1100º Centigrade. The carbon is burned off leaving unslaked lime (CaO).The unslaked lime that comes out of the ovens is a porous raw material in the form of various sized small stones. It’s color ranges from white to light yellow.
Transforming the Unslaked Stones into Lime
The unslaked lime (CaO) is then mixed gently and slowly with water. This reaction develops high temperatures (150º C) and increase the volume of the mix by 10%. The reaction causes the stones to crack and water vapor is released. Water is added incrementally as this occurs and carefully mixed into the “paste.”
Hydrated Lime (extrafine lime)
This is produced by carefully monitoring the water and unslaked stone mix until the exact proportion of water is the same as in limestone. It is dried and ground into powder. Hydrated lime is sold by the bag like cement. This product is extremely frost resistant.
Slaked Lime Putty (Grassello)
This formulation has a higher water content that hydrated lime (ratio 3:1). It is best described as a “fatty mass” called slaked lime putty or Grassello.The Romans aged the lime putty in clay urns under ground immersed in water for months. Today, the lime putty is still soaked in water for up to 25 months to slake it properly. “Grassello” is sold ready to use in plastic containers.
Grip and Setting
The principal characteristic of lime, when properly mixed and applied, is that it produces substances that are durable, stable, strong and water-resistant. This charcteristic is based on the chemical reaction between slaked lime and natural carbon dioxide in the atmosphere. While the product dries, water evaporates which produces calcium carbonate of lime (Ca CO3). This is called the “carbonization reaction” meaning the lime returns to the exact chemical composition of its parent stone but with crystals much smaller than in the original stones. The carbonating process is very slow (minimum 3 months to cure) due to the low concentration of carbon dioxide in the air. Slaked lime is always used with other natural mineral components such as marble dust or titanium to prevent cracking.
Full Cycle of Lime
Here is the chemical reaction for the lime process: Limestone containing Calcium Carbonate (CaCO3) is crushed and burned at high temperatures:
CaCO3 -----> CaO (Calcium Oxide) + CO2 (Carbon Dioxide) which evaporates.
-the process to slake and age the lime before use starts:
CaO + H2O -----> Ca (OH)2 which is Calcium Hydroxide (putty lime or Grassello)
-when the Grassello is applied, the Carbonation reaction starts right away, picking up natural CO2 molecules from the atmosphere and
evaporating water:
Ca (OH)2 = CO2 -----> CaCO3 (Calcium Oxide or LIMESTONE again!) plus H2O which evaporates.
The limestone becomes limestone again (without any impurities)!!!
That is why lime is so durable, environmentally friendly and beautiful – as long as synthetics are not added to it!
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