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Tadelakt Technical Guidance

Water-resistant lime-based finish for wet or moderately exposed areas.

Tadelakt is a traditional Moroccan lime finish that creates a seamless, tactile and highly water-resistant surface. Its performance comes from a combination of lime chemistry, careful timing, mechanical compression and saponification with soap. It is particularly well suited to showers, bathtubs, basins, niches and other surfaces where a continuous mineral finish is desirable.

Tadelakt is also a craft system rather than a fixed recipe. Lime quality, aggregate, substrate porosity, temperature, humidity, application thickness and timing all affect the result. The following should therefore be treated as a working framework to be tested and refined rather than a universal formula.

1. Things to know when choosing tadelakt

Strengths

  • Seamless and highly tactile

  • Naturally water-resistant when properly compressed and saponified

  • Suitable for walls, curves, niches, basins and bathtubs

  • Mineral and low-material compared with many manufactured finishes

  • Can develop a rich patina over time

  • Repairable and maintainable

  • Particularly expressive when used continuously across architectural elements

Sensitivities

Tadelakt is more sensitive to movement, substrate preparation, geometry and application timing than conventional tile or cement finishes.

Long-term performance depends on:

  • A stable substrate

  • Appropriate porosity and suction

  • Good mechanical keying between coats

  • Correct curing conditions

  • Correct timing between coats

  • Consistent compression

  • Even soap absorption

  • Careful detailing at corners, joints and penetrations

Natural variation in colour, sheen and texture should be expected. On white and pale finishes especially, differences in moisture content, compression and soap absorption can produce visible tonal variation.

2. Materials & Tools

Lime

  • Slaked lime — Ca(OH)₂

  • Preferably lime with a documented and sufficient slaking/maturation period; minimum 3 months should be verified with the lime supplier.

  • For lime putty, dilute with clean water to approximately a toothpaste consistency, allow to rest for ~24 hours and break down any remaining lumps before use.

Aggregates

  • Coarse, clean sand for the base coat

  • Fine marble dust for the tadelakt coats

  • Aggregate grading should be adjusted according to the required thickness and working characteristics.

Tools

  • Clean, flat trowels

  • Spray bottle

  • Smooth, flat river pebble or equivalent polishing stone that sits comfortably in the palm

  • Clean mixing vessels

  • Clean workspace and tools

Soap

  • Olive-oil-based Castile soap can be used experimentally as a substitute for traditional Moroccan black soap.

  • Commercial Castile soaps vary considerably in concentration and composition, so dilution should be established through testing rather than assumed to be chemically identical to traditional savon noir.

3. Overall Assembly

The general sequence is:

Structural assembly
↓
Lime-sand base / scratch coat
↓
Multiple lime-marble dust coats
↓
Compression and shaping
↓
Soap application + stone polishing
↓
Curing

The receiving substrate should be stable, mineral, clean, suitably porous and mechanically keyed.

Tadelakt should not simply be applied over a smooth, sealed or otherwise incompatible surface. Existing cement renders, waterproofing treatments, paints or other coatings should be assessed for their porosity, adhesion, vapour behaviour and compatibility with the intended tadelakt system before proceeding.

4. Structural Assembly & Substrate

Suitable structural assemblies may include:

  • Fired brick masonry

  • Stone masonry

  • Other stable mineral masonry systems

Where possible, a lime or lime-cement mortar can provide a more compatible transition between masonry and the lime render than a dense, highly impermeable cement-rich assembly.

The objective is not simply to make the wall waterproof. The structural assembly should provide a stable, continuous and predictable substrate for the lime system above it.

Important

If a contractor has already applied a cement render, waterproofing admixture or other proprietary coating, do not automatically proceed or demolish it. Establish:

  • Exact product and dosage

  • Thickness

  • Substrate condition

  • Surface porosity

  • Mechanical bond

  • Moisture behaviour

  • Compatibility with the intended tadelakt mix

Where longevity is critical, the complete assembly should be considered rather than evaluating individual materials in isolation.

5. First Coat — Lime-Sand Base / Scratch Coat

A substantial lime-sand coat provides the continuous mineral substrate for the tadelakt.

Typical thickness

Approximately 10–15 mm, adjusted according to:

  • Substrate porosity

  • Surface irregularity

  • Aggregate grading

  • Required moisture regulation

  • Overall wall geometry

A less porous substrate may require the lime base coat to perform more of the moisture-regulating and bonding work.

Mix

There is no universal ratio because lime strength, sand grading and moisture content vary.

As a working reference:

Valentino’s slaked lime: approximately 1 part lime : 2.5 parts coarse sand, with particle size <8 mm.

This ratio should be adjusted through testing.

Application

Mechanical keying between the structural substrate and the lime coat is critical.

The surface should remain rough and receptive, rather than being polished or closed.

Initial curing

Allow the coat to cure until it reaches a firm set state.

As a practical guide, this may be at least ~48 hours, but the actual condition of the material is more important than elapsed time.

The coat should be sufficiently hardened that significant pressure causes it to break rather than shift or deform.

During early curing, protect the plaster from excessive heat, wind and rapid drying. Light misting may be used to maintain a damp condition where necessary.

Damp, not saturated.

The objective is to allow controlled carbonation/hydration while preventing premature drying.

6. Lime + Marble Dust Coats

Once the base coat has sufficiently set, begin applying the finer lime-marble layers.

Starting ratio

A 1:1 lime-to-marble-dust ratio by volume is a useful starting point, but the exact proportion depends on:

  • Lime quality

  • Marble dust grading

  • Desired finish

  • Water content

  • Working characteristics

The final mix should be soft and workable — slightly wetter than a firm putty, but not fluid.

Always establish the final mix through a test panel.

Application

Apply multiple thin coats rather than one thick coat.

Uniform thickness is important.

The timing between coats is critical.

The previous coat should be sufficiently firm that the new coat does not displace or drag it, while still retaining enough moisture and key for good adhesion.

This condition is referred to as the:

GREEN STATE

Green state

A green coat is:

  • Firm enough to support the next operation

  • Still relatively moist

  • Not fully cured

  • Not brittle

  • Still receptive to mechanical and chemical interaction

The precise timing will vary with climate, substrate suction, thickness and mix. ~1–2 hours may be a useful starting point for experimentation, but should not be treated as a fixed rule.

7. Compression & Shaping

After the final lime-marble coat has reached an appropriate green state, begin compressing the surface.

Sequence

Trowel → stone

Begin with the trowel to close and consolidate the surface, followed by the smooth polishing stone.

Use:

  • Small movements

  • Consistent pressure

  • Overlapping passes

  • Continuous attention to surface uniformity

For horizontal surfaces, work generally toward the drainage point.

For vertical surfaces, consider how water will naturally move across the finished geometry.

Edges and local cracking

Small local cracks or edge breaks may occur during compression, particularly around:

  • Corners

  • Undulations

  • Changes in geometry

  • Areas with different curing rates

If the material is still green, lightly re-wet the area and massage the material back into position.

If cracking spreads through the underlying layers and pulls material out with it, the area may have passed beyond the workable green state. In this situation, patching the surface may not be sufficient; the affected area should be assessed and potentially removed and reapplied.

Timing is critical.

8. Transition to Leather-Hard

After compression, allow the surface to become somewhat firmer.

The next useful working condition is often described as:

LEATHER-HARD

At this stage the material is stable enough to resist deformation but is not yet fully cured.

As a rough working reference, this may occur approximately 2–4 hours after compression, but again, physical condition is more reliable than elapsed time.

9. Soap + Stone Polish

Before applying soap, check that the surface is evenly dry.

Visual check

Look for variations in colour or tone.

Dark areas may indicate retained moisture.

These areas should be allowed to equalise before saponification because soap can seal moisture and create persistent tonal variation.

Smear test

Lightly test an inconspicuous area with the polishing stone.

If significant material transfers to the stone, the surface is still too wet.

If the surface is firm and stable, proceed.

At this stage it is generally safer to be slightly more cured than too wet, provided the surface is still receptive to saponification.

10. Soap Dilution & Saponification

For initial testing with Castile olive-oil soap:

Start around 1 part soap : 6 parts clean water.

This should be treated as an experimental starting point rather than a universal ratio.

Different Castile soaps have different concentrations and oil compositions. A test panel should establish the appropriate dilution before committing to the finished surface.

Application

Mist a small section with the diluted soap and immediately work it with the smooth stone.

The aim is to:

  • Introduce soap into the lime surface

  • Continue compressing and burnishing

  • Develop a dense, smooth and subtly waxy surface

  • Create calcium soaps through saponification

Work methodically in small sections.

Avoid flooding the surface.

The objective is to introduce sufficient soap into the lime to achieve saponification, not to leave a layer of soap sitting on the surface.

Excess or unevenly absorbed soap can contribute to:

  • Cloudiness

  • Dark patches

  • Uneven sheen

  • Discolouration

This is particularly noticeable on white and very pale tadelakt.

Pay special attention to:

  • Corners

  • Undulations

  • Seams

  • Junctions

  • Changes in plane

  • Areas around fixtures and penetrations

11. Post-Soap Curing

Once saponification is complete, do not continue misting the surface as though it were an ordinary lime render.

The soap-treated surface is intentionally becoming water-resistant.

Allow the tadelakt to dry naturally while carbonation continues within the mineral layers.

Initial curing

Allow approximately 24 hours before carrying out an initial water-resistance test.

Avoid flooding or using the surface during this early period.

Water test

Place a few drops of clean water onto the surface.

A successful saponified surface should cause water to:

  • Bead

  • Sit on the surface

  • Or run across it rather than immediately being absorbed

Some variation in absorption may occur due to differences in soap concentration, plaster density and surface porosity.

If absorption remains significant, a further light soap-and-polish treatment may be considered after allowing the surface to stabilise.

12. Long-Term Curing & Use

Allow the finished system to continue curing without deliberate misting or additional water for several weeks.

The underlying lime continues to carbonate as it reacts with atmospheric CO₂.

For the first months of use, particularly in wet areas:

  • Allow surfaces to dry completely between uses

  • Squeegee standing water after bathing/showering

  • Avoid harsh or acidic cleaning products

  • Avoid abrasive scrubbing

  • Maintain good ventilation

The surface should develop increasing hardness and stability over time.

With good workmanship and appropriate use, maintenance should be minimal. Periodic gentle cleaning and, where necessary, re-soaping after several years can help restore the surface’s water resistance and sheen.

13. Critical Variables to Record During Testing

Because tadelakt is highly dependent on local materials and conditions, every project should establish its own tested recipe.

Record:

  • Lime source and age

  • Lime-to-aggregate ratio

  • Aggregate type and grading

  • Water content

  • Coat thickness

  • Time between coats

  • Temperature

  • Relative humidity

  • Substrate porosity

  • Time to green state

  • Time to leather-hard state

  • Soap type and concentration

  • Polishing timing

  • Number of soap applications

  • Drying behaviour

  • Water-beading behaviour

  • Final colour and sheen

A full-scale test panel is strongly recommended before beginning a critical wet-area installation.

The test panel should ideally reproduce the actual conditions of the finished work, including:

  • Actual substrate

  • Actual lime

  • Actual marble dust

  • Actual soap

  • An internal corner

  • A change of plane

  • Any significant junctions or penetrations

The goal is not to follow a recipe perfectly; it is to establish a repeatable material process with the particular lime, aggregates, substrate and climate available on the project.

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