Tadelakt: the Marrakech lime plaster, its technique, uses and mistakes

Tadelakt is the most copied and least understood Moroccan finish. Sold everywhere as “Moroccan lime plaster”, it is often applied to the wrong substrates, with limes that are not its own, by hands that do not polish it, and then blamed for cracking or staining. This guide says what it is, according to the laboratory analyses published on Marrakech lime, how it is applied, where it belongs and where it does not, and which mistakes explain most failures. It belongs to the materials series of the Moroccan architecture pillar.

What exactly is tadelakt?

Tadelakt’s singularity lies in its lime. The team of El Amrani, Polidoro, Ibnoussina, Fratini and colleagues, who studied the material “from the stone to the lime”, describe a plaster “realized using a particular hydraulic lime produced in the outskirts of Marrakesh”, from a carbonate stone whose nature explains the product’s properties. Their conclusion is the point to remember: “the lime for Tadelakt is not a simple binder but a ready-to-use material that does not need the addition of any aggregate but only water, and pigments if necessary”. In other words, the traditional firing of a marly limestone leaves in the lime an uncalcined fraction and a siliceous fraction that act as sand; the craftsman has nothing to proportion.

A 2024 study at the National School of Applied Sciences in Agadir confirms this composition on market samples: a lime that is “slightly hydraulic”, “mainly composed of calcite, belite, calcium oxides, silicon, and carbons”, produced “from marly limestone traditionally fired in the Marrakech region”, in which about 24 % of the particles, the finest, form the binder phase and the rest the aggregates. The authors recall that “for over eight centuries, Marrakech has been producing the lime plaster known as Tadelakt”, used “specifically to cover areas in contact with water”, and that it “consists substantially of lime, water, black cleaner, and several colorings”.

How is it applied?

1. The substrate. A rigid, stable, rough base compatible with lime: lime or lime-cement render, brick, roughened concrete. No gypsum plaster, no paint, no flexible boards.
2. Mixing. Marrakech lime and water, with lime-fast natural pigments for colour; the paste is left to rest.
3. Application. One thin coat, compacted with the trowel in several passes as the surface stiffens.
4. Stone polishing. While the plaster is still fresh but firm, the craftsman compresses and smooths it with a hard stone, at length, until the pores close and the sheen appears.
5. Black soap. A solution of black olive soap applied and polished again: the soap reacts with the lime to form an insoluble calcium soap at the surface that completes the water-proofing.
6. Drying and care. Slow hardening by carbonation; maintenance with black soap, never acid or abrasive cleaners.

Selkani sums up its use: tadelakt is “a fairly expensive ornamental coating used for the front of Riads, Mediterranean palaces, but also to cover the walls of hammams exposed to water, as well as fountains, bathtubs, basins, and sinks”; it is “a colorful lime coating that can be put to the ground both inside and outside, protecting the walls from dampness”. The cost lies in the labour of polishing, not in the material.

Why does it resist water?

Being slightly hydraulic, Marrakech lime contains belite, a calcium silicate that sets on contact with water; that is what distinguishes it from a pure air lime. But tadelakt’s water-tightness is first mechanical and chemical: stone burnishing reduces surface porosity, and the black soap, reacting with calcium hydroxide, forms a water-repellent film. A Marrakech lime plaster merely trowelled, without polishing or soap, is not tadelakt and is not watertight.

What the material is not must also be said. The Agadir study measured the compressive strength of Marrakech lime concretes: “not exceeding 1 MPa in the best cases”, a very low value due “to the sandy nature of the aggregates and the traditional lime production process, which does not allow for effective quality control of the final product”. Tadelakt is a finish a few millimetres thick on a substrate that carries the load; it carries nothing itself, and its quality varies from one kiln to another.

Where does it belong, and where does it not?

Why did it almost disappear?

The authors of the Agadir study report that “the Tadelakt method almost disappeared from Morocco in the early 1970s, in favor of new premixed ingredients that allowed for a faster application process”, and that “renewed interest in traditional architecture, particularly in Marrakech, was a major factor in its return in the 1980s”. UNESCO records the same movement at the scale of the medina: the restoration of houses “has tremendously revived the artisanal trades linked to construction”, and expressly names “lime plaster (tadallakt)” among them. Tadelakt is today “appreciated all over the world for its waterproofing capabilities, durability, beauty, and variety of colors, as well as its increasingly appreciated ecological components”.

That success has a downside: worldwide demand has produced products called “tadelakt” that use neither Marrakech lime nor stone polishing. They are lime plasters, sometimes excellent ones, but of another nature; the word has become a style more than a technique.

Which mistakes explain the failures?

• A substrate that moves or does not key. Plasterboard, old paint, smooth unscabbled concrete: the plaster cracks or detaches. Tadelakt wants a rigid, rough base.
• A lime that is not Marrakech’s. A pure air lime or an industrial blend contains neither the aggregates nor the hydraulicity that make the material; the result is a stucco, not tadelakt.
• Polishing cut short. Stone burnishing is long and tiring; it is what closes the pores. A matt, porous tadelakt was polished too little or too late.
• Black soap forgotten or replaced. Without the lime-soap reaction the surface stays absorbent.
• Detergent cleaning. Acids, bleach, limescale removers attack the lime and dissolve the film; only diluted black soap is suitable.
• The wrong place. Worktop, shower without waterproofing under the plaster, kitchen floor: uses the tradition never provided for.
• Expecting structural strength. A Marrakech lime concrete tops out below 1 MPa in compression; tadelakt is a skin, not a screed.