With the modern development of natural building technologies, there has been a resurgence and rediscovery of ancient and traditional methods of plasterwork. For over 10,000 years, in nearly every culture, humans have used lime as an applied material that serves as both function and decoration. From the frescoes of the Italian Renaissance to the sculpted bas relief masks of the ancient Mayans, the chemistry, durability and elegant beauty of lime has, until modern times, been a staple of art and architecture the world over. In the twentieth century, builders have all but forgotten how to work with earth and lime based mortars, and plasters. Thanks to the efforts of passionate builders, craftspeople, architects and designers, and many within the natural building community, these old ways are being revived and put into practice once again. Collectively we are relearning how to successfully formulate and apply traditional plasters, using locally sourced materials and modern tools.
The rich and mysterious culture of Morocco offers one example of an ancient lime plaster art, nearly lost, which is now enjoying a rebirth – Tedelakt
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Tadelakt is a waterproof, polished plaster made from lime and finished with olive oil soap. The history of this highly specialized technique dates back many thousands of years. It has its origins in and around the ancient city of Marrakech at the foot of the High Atlas Mountains. The Berbers, some of the indigenous
peoples of North Africa, discovered the magical water resistant chemistry of lime treated with soap. In the beginning, tadelakt was used as technique to waterproof earthen cisterns. The ability to effectively and hygienically store water was a major development. It was not long before tadelakt became recognized as a beautiful finish technique that could be pigmented and applied on any surface, especially where moisture was prevalent. Eventually, Tadelakt became a highly prized surface treatment that was widely specified in the traditional North African hammams (communal bath houses) and royal palaces. To this day in Morocco the tadelakt technique is passed down as an oral tradition from master to apprentice in an unbroken lineage that dates back to antiquity.
The word “Tadelakt” comes from the Arabic verb “dlek” which means to rub, or perhaps most appropriately, “to caress”. The word “dlek” describes the final step of finishing where a smooth stone is used to burnish the lime. Olive oil soap is applied during the final polishing and the tadelakt is burnished to a brilliant luster. In an interesting chemical reaction, the stearic acid in the soap combines with the free calcium of the fresh lime to create calcium stearate, a water resistant wax like material.
The allure of tadelakt is not easily described in words or pictures. It is only through touching it that you can fully appreciate this unique finish. A tadelakt surface is at once hard as stone and soft as silk. The combination of the soap and lime creates a living, breathing surface that appears to be part stone, part leather, shiny and smooth. Unlike some other plasters, tadelakt is not a
standardized finish. Walls look rustic, and hand crafted. Tadelakt has a shiny, slightly wavy appearance and is colored with the same mineral pigments that have been used since antiquity. Over time, the lime develops a patina that creates a subtle ever-changing lumination. Properly applied, tadelakt develops a network of very fine hairline cracks that add to the ancient appearance of the finish. Because of its unique characteristics tadelakt can be made to seamlessly cover walls, ceilings, floors, sinks, showers, fountains and even bathtubs.
I first discovered the tadelakt technique in 2005, while searching the Internet about ancient plaster techniques. I was instantly captivated by the possibilities. At the time there was almost no information in English. Most of the websites were in French or German. I was hopelessly fascinated and determined to figure out this mysterious art. I forced myself to read the French websites and figure out as much as possible. Having worked with lime plasters for many years, I had a good idea of where to start experimenting. After much trial and error, I had produced some pretty good results on small objects. I still had many questions and did not feel confident enough to do a real world application. More internet research turned up a 5-day tadelakt course offered in Marrakech. The course taught the tadelakt technique in the traditional way, using the mysterious “lime of Marrakech.” Everything I had read told me that tadelakt can only be made with this special lime from Morocco. This was something that I did not understand, and was concerned about. In all of my work I strive to use materials that are as local as possible. I would have had a very hard time on with the idea of importing special material half way around the world. I was determined to find out if there was something special about the Moroccan lime or if I could create a similar mix using more locally sourced materials. For me, signing up for the course in Morocco seemed like an obvious next step.
My experience in Morocco was inspiring to say the least – an awe-inspiring blend of sights, sounds and colors. The old city of Marrakech dates back over 1,000 years. The tall earthen buildings form a haphazard labyrinth of endless narrow streets and alleyways, all protected from the outside world by massive earthen ramparts that surround the entire city. I have never seen so much architectural art and artistic decoration. From the grandest royal palace to a simple teapot, almost everything was ornately detailed with complex repeating geometric designs.
During my tadelakt course, I learned the traditional technique. We worked with roughly the same basic tools that have been used for centuries. A masons trowel, a wood float, and a stone with one flat, smooth side. I discovered that what was “special” about the “lime of Marrakech” was in the way that the lime is produced. The Moroccan limekilns are burned in the open air. A hole is dug in the ground for the fire, and grapefruit sized pieces of limestone are piled high above in a way that creates a dome like structure above the fire. An oily sage like plant is used for fuel to fire the kiln. This way of burning lime probably has not changed since antiquity.
The lime that is produced has unique properties. Because these open-air kilns are thermally inefficient, only about the outer two-thirds of the limestone is calcined. The inner core does not get hot enough to convert to calcium oxide. This creates a lime that consists of about 50% inert limestone particles. These particles play the role of sand in the tadelakt mixture. It is also worth noting that the lime of Marrakech has some clay impurities and is therefore slightly hydraulic.
Having seen first hand what was special about the traditional tadelakt lime I returned home, hopeful that I could create something similar using more locally sourced materials. All I needed to do was to find some good limestone based sand that would replicate the inert limestone in the traditional material. At my local plaster supply store, I found crushed marble sand that was sold as aggregate for white swimming pool plaster finishes. It was fine, but not too fine, and best of all it is quarried less than 150 miles from where I live. I tried mixing it 50/50 with Type S lime putty and began to make some tests. I was pleasantly surprised with the results. The tadelakt was very shiny, waterproof and super-durable. To this day I have not changed this formulation much at all and have used it on every one of my tadelakt projects.
