The art of Tadelakt has for centuries been steeped in mystic and wonder. Few who leave the fantastic halls of the Marrakesh palaces or the beautifully reconstructed Riads will fail to notice the glimmering monolithic plaster that twinkles in the light as it seamlessly extends over these proud buildings. Tadelakt is a plaster finishing technique historically used in north Africa to protect earthen structures. It is specifically valued for its function of providing a water proof seal. Marrakesh, a wonderfully unique city that has remained virtually unchanged for centuries, provides insights and inspiration for this technique as it is re-discovered throughout the natural building community.
The climate–appropriate buildings of Marrakesh feature huge 6ft thick earthen walls, which tower up into the relentlessly hot desert skies. This provides generous shading for the winding streets, while the large thermal mass of earth mitigates the extremes of the desert climate. As with most natural buildings, protecting them from moisture and rain is the largest challenge. Although Marrakesh receives very little rainfall, water related issues still exist, primarily from within for drinking, bathing and cleaning. If everything is made of earth how do you have these wet areas within your house? Tadelakt provides a unique and effective solution to this challenge.
A Renaissance in use
Tadelakt is a technique to finish a lime plaster. It involves using a particularly high lime-to-aggregate ratio which is applied in multiple thin coats to a substrate, such as an earthen wall surface. It is then polished with a trowel and burnished with precious stones. Finally. it is rubbed down with soap; traditionally black olive oil soap. Its primary use was emphasized in areas that often get wet, typically bathrooms and fountains, but not excluding waterproofing entire swimming pools.
The modern renaissance of Tadelakt has been brought about by the same necessity as the ancient Moroccan builders had, protecting earthen structures from water. This is an exciting tool for all natural builders to have in their belt, but it is important to remember the climatic differences that the Moroccans faced and the centuries of perfecting this art that took place in order to produce a product that was and still is so effective.
Last year in order to begin re-establishing this knowledge base we brought in Ryan Chivers of Artesano Traditional Plasters and Liz Johndrow of Earthen Endeavors to our site, Rancho Mastatal, in Costa Rica to teach a week long workshop on lime plastering and Tadelakt. Ryan is a modern day North American artisan who has done as much as anyone to understand and practice Tadelakt. Since this wonderfully successful course we have been practicing this technique which seamlessly complements our own knowledge of lime plastering learned over the last decade of natural building at Rancho Mastatal. We will be offering this Natural Building Intensive workshop again in March and April of 2015.
The Tadelakt Technique
It is important to emphasize that Tadelakt is an advanced technique that requires a knowledge of the process, materials at hand, and ample testing. Anyone interested in practicing is encouraged to start small, find a mentor with experience, or take a course. The following photo series and set of instructions show the process of applying a Tadelakt coat to the inside of a wattle and daub shower.
Tools: 1/16th inch sifter, misting hose head or spray bottle, a wooden or sponge float, a plaster trowel, and a burnishing stone.
55% Lime putty
45% Aggregate in the form of lime sand
All sifted through a 1/16th inch screen
Lime putty comes from slaked lime that we get directly from the kiln and have been soaking in water for years. This has given us a unique lime putty to work with which will of course vary depending on your region. As with most natural building techniques there is no set recipe and mixes will depend on the particular material at your disposal. In the US and Europe it is not uncommon to be able to buy lime (known as pressure hydrated Type ‘S’ lime in N. America) as a standardized product. Much more accurate recipes can be formulated based from this.
Lime sand is raw crushed limestone that is commonly sold as agricultural lime.
As with most natural building the preparation of your surface, in this case an earthen wall, is important. The smoother and flatter your wall, the better; this will reduce spots where the lime is not of uniform thickness. A small amount of scratching can help increase surface area for contact between the wall and the coming Tadelakt coat.
To begin: get the substrate wall wet, keep soaking until the water doesn’t seem to be getting absorbed in; it is better to be on the wet side. We use a garden hose with a misting function.
Put test pieces of the Tadelakt mixture on the wall to see how quickly they dry. This will help gauge where more water is needed. The goal is to have everything dry evenly and consistently.
Apply a very thin even coat of the Tadelakt mix using the wooden float or sponge float. This coat should to be just thin enough to cover the substrate wall.
Wait until the wall absorbs moisture from the Tadelakt. It needs to be dry enough so another coat can be applied that will build thickness, if it is still too wet you will just spread the first coat around. This time will vary upon how wet you get your wall and what the wall is made from. This could be as short as minutes or as long as hours. Always be aware of the sections of your wall which are drying first. These are the areas you will work first as you add more layers.
Repeat this process and apply a third coat. You need at least three coats.
On the final coat you need to begin smoothing the surface with a trowel; filling all micro gaps and creating a compressed smooth surface. A lime rich cream will come to the surface as you compress the aggregate into the wall when using a steel trowel. Use this cream to repair gaps, holes and clean the edges using the point of the trowel to define them. Aesthetically speaking, clean edges equal a tidy looking middle.
This is time sensitive: if you do it too soon you just spread the mixture unevenly and if you wait too long you scratch it and cannot smooth it effectively. This takes time and experience to learn but hopefully you have built some knowledge of how the wall is acting in your previous coats.
The next step will depend how long the mixture is taking to dry. You need to compress the surface further by burnishing with a stone If the mixture is too wet it will slurry, bringing too much cream to the surface and roughing up the surface again (this can easily be fixed with the Japanese trowel). Stone the surface repeatedly until a smooth surface has been created. Let this sit over night.
Precious stones are used that have a hardness rating on the Mohs scale of 7 or more. Use the flattest face in a manner not to dissimilar to a Mr Miyagi wax-on, wax-off technique to burnish the wall.
The next day apply soap to the wall and burnish with the stone once more. Your goal is a shiny surface. To accomplish this keep feeding the surface soap and burnishing. Any natural soap will work as the soap (stearic acid) chemically binds with the lime (free calcium) to create a layer of calcium stearate which is very hydrophobic. We use the soap we make at Rancho Mastatal from lard, palm oil and potassium hydroxide. For the next couple of days thinly apply soap to the surface by rubbing it in with your hand or a brush. Now step back and admire.
The result of all this work is a waterproof and beautiful surface that will last the test of time.
Natural Building Intensive in Costa Rica
Workshop in Costa Rica, March-April 2015
For anyone interested in gaining first hand experience in Tadelakt, as well as the full spectrum of earth building and lime plastering techniques, consider joining Ryan Chivers, Liz Johndrow, and the Rancho Mastatal team this March 31 to April 11, 2015.
Information on the curriculum, instructors, accommodations, and costs can be found on our website here. Please don’t hesitate with any questions and we hope to see you in Costa Rica soon!