Tadelakt is a waterproof plaster surface used in Moroccan architecture to make baths, sinks, water vessels, interior and exterior walls, ceilings, roofs, and even floors. It is made from lime plaster, which is rammed, polished, and treated with soap to make it waterproof and water-repellant. Tadelakt is labour-intensive to install, but durable. Since it is applied as a paste, tadelakt has a soft, undulating character, it can form curves, and it is seamless. Pigment can be added to give it any colour, but deep red is traditional. It may have a shiny or matte finish.

Etymology and history
“Tadelakt” means “to rub in”, from Amazigh/Berber.

Tadelakt is thought to have evolved from qadad, a similar plaster treated with calcium hydroxide and oils and fats instead of soaps.

Constituents and chemistry
The basic constituents of tadelakt plaster are:

lime plaster (not Portland cement)
in some cases, marble or limestone sand (but not other aggregates)
natural soap (often “black” or olive oil soap) to speed carbonation of the surface and impart water-resistance.
The soap chemically reacts with the lime plaster, forming lime (calcium) soaps. Calcium soaps are insoluble in water, and fairly hard. They are familiar, in areas with calcium-rich (“hard”) water, as deposits in bathtubs, sinks, and showers; when soap is mixed with the water’s dissolved calcium carbonate/lime, calcium soaps form.

2 C17H35COONa+ + Ca2+ → (C17H35COO)2Ca + 2 Na+

Traditional application includes polishing with a river stone and treatment with oleic acid, in the form of olive oil soap, to lend it its final appearance and water resistance.

In Morocco, the traditional application technique:

plaster powder is mixed with water for 12 to 15 hours prior to the addition of pigment.
the plaster is applied in one thick coat with a wooden float, and smoothed with the same.
before the plaster sets, a flat, smooth, hard stone is used to compress the plaster, then a plastic trowel used for the final polish.
it is mechanically polished using stones or abrasives harder than the plaster, providing a smooth, sometimes shiny, finish.
lastly, an olive-oil soap solution is used to seal the plaster
Long-term maintenance of tadelakt requires regularly re-sealing the surface with a soap solution; in the case of qadad rooves, this was traditionally done every few years.

Tadelakt can be elaborately carved into yeseria.[citation needed]

Tadelakt is the traditional coating of the palaces, hammams and bathrooms of the riads in Morocco. The restoration of the riads of Morocco had led to a resurgence in its use.

In modern times, it has been used outside.

His pose is a meticulous operation that is not within the reach of all. Moroccan master craftsmen are called maalem and only take this title after several years of practice. Tadelakt is a brittle mortar that requires regular maintenance. Each luster must be repaired or it may be infiltrated into the support and retouching is always visible.

The tadelakt is applied in two passes. The first will serve as a layer of attachment: gobetis. the second will be lime plaster tadelakt. Applied to the wooden trowel and then troweled. After a variable rest period when the plaster begins to dry, it is rubbed with a plastic pallet or roller to polish the plaster until it shines. Egg white is sometimes used during this first polishing to increase the surface hardness.

When the plaster is completely dry but before it actually begins to carbonate (usually the next day), the surface is coated with diluted black soap (not all soaps are suitable: it requires a partially saponified soap to get the chemical reaction adequate giving the final seal to the coating, low soap of olive oil or linseed oil) and again polished to obtain a “mirror effect”.

Note that it is possible to work a lime paint in the same way for an effect approaching, but not having the effect of depth tadelakt.

The biggest achievement in tadelakt is the Casablanca Twin Center, designed by the contemporary architect Ricardo Bofill: it is about two twin towers 110 meters high (29 floors), completely covered with a white tadelakt. In Morocco, several contemporary buildings have used the tadelakt as a decorative coating: Royal Theater of Marrakech, Hotel Mogador in Essaouira.

The industrial tadelakt
Following the many articles published in decorating journals and the popularity of the international jet set for Marrakech, public interest in tadelakt has led manufacturers to create modern materials with the appearance of traditional tadelakt. If some manufacturers condition true Moroccan lime, its installation and maintenance require a knowledge of the technique of tadelakt.

New products derived from a lime-based blend from Marrakech approach the aesthetic and technical qualities of traditional tadelakt while being more resistant and with ease of installation adapted to Western habits.

The knowledge of the chemical composition of the Moroccan lime makes it possible to obtain a good imitation by a mixture of aerial lime, hydraulic lime and very fine minerals generally of the marble powder. This product is close to stucco .

Other products are essentially bastards of cements and lime. Some cement manufacturers combine synthetic products with cements for fast adhesion and strength and a glossy finish. The pose is very simple, but the aesthetic result moves away from the tadelakt. Most of these modern materials have to be protected from moisture by varnishes to prevent the surfacing of calcareous salts (efflorescence).

Qadâd, the ancestor of tadelakt
In Sanaa, Yemen , qadâd 1 consists of a mixture of lime and sand from volcanic stones. Before use, the black and porous lava is washed. Depending on the region, lava is replaced by river sand. The oral tradition mentions the presence of organic elements sometimes mixed with qaddd or lime milk: addition of sugar, eggs or camel milk. In Europe, since antiquity, we know a series of non-organic ingredients that allowed a better consistency of the plaster: pumice, lava, powder of clay tiles, chippings of clay, refractory clay in different granulometries. The term qadâd refers to a very old coating technique. It was already used in the 8th century BC. J. – C. (the dam of Mârib). Its composition and manufacture differ by region, geology and climate. Like all natural building materials, qadâd acts as a temperature regulator and is rather refreshing. Its impermeability, its extreme longevity, its antiseptic properties make it play a great architectural role, especially in cisterns. It is applied to cover roof terraces. It is often destroyed by the owners and replaced by plaster or cement. Such interventions cause irremediable losses, among other things because qadâd was often adorned with beautiful motifs (the case of mosque domes in Sanaa of Mahdî Abbâs and al-Mutawakkil). The use of qadâd is expensive, because of the number of men needed and the time of execution. It is difficult for a private individual to have his roof covered in qadâd. New techniques and forms of construction have appeared since the 1962 revolution and the opening of Yemen. Cement has totally supplanted qadâd. As a result, qadâd initially fell into oblivion and was no longer transmitted to new generations of masons. For the restoration projects of the 1980s, we had to look for former master craftsmen. Today, there is a strong interest in the conservation of this technique and its use in restorations.

Source From Wikipedia