Khorasan Mortar: What is it, and how is it made?

Khorasan Mortar: What is it and How is it Made?

Khorasan mortar, which has been used in historical structures for centuries, holds an important place in architecture thanks to its durability and long-lasting nature. Traditionally prepared with ancient methods, this mortar has been preferred throughout history especially for its resistance to water and moisture. Today, it continues to be applied not only in restoration projects but also in various fields of engineering and architecture, often in combination with modern flooring chemicals.

In this guide, you will explore in detail the definition, composition, preparation stages, properties, and usage areas of Khorasan mortar.

What is Khorasan Mortar?

Khorasan mortar is a traditional building material obtained by mixing lime with brick dust or ground pieces of baked clay in specific proportions. Its origins date back to the Roman and Byzantine periods, and it was used in the construction of many historical structures up to the Ottoman era. Its resistance to water and moisture made it indispensable in structures such as bridges, aqueducts, baths, and cisterns that were directly exposed to water or humid environments.

One of the most striking features of this mortar is that, over time, it hardens into a stone-like solid form. This chemical and physical transformation allowed the construction of structures that could stand strong for centuries. This durability also makes it crucial in today’s restoration work. To preserve the authenticity and originality of historic structures, Khorasan mortar remains the closest material to the original.

Materials of Khorasan Mortar

The unique durability and properties of Khorasan mortar come from the careful selection and precise proportions of its ingredients. The main traditional components are:

• Lime: The fundamental binder of the mortar. It gradually carbonates, playing the main role in the hardening process.

• Brick Dust or Crushed Baked Clay: These pozzolanic materials accelerate the reaction of lime with air, giving the mortar water resistance and additional strength.

• Sand: Provides bulk to the mixture, balances consistency, and makes application easier. Think of it as the skeleton of the mortar.

• Water: Binds all components into a homogeneous, workable paste. Water is also essential for the chemical reactions to begin.

In some regions, natural stone fragments known as horasan stone or finely ground mineral additives were included in the mixture. These enhanced the mortar’s lifespan and resistance to both moisture and pressure. Each region developed its own unique formula of Khorasan mortar based on local resources and climate.

How is Khorasan Mortar Made?

The most important aspect in preparing Khorasan mortar is maintaining precise proportions and following correct procedures. Traditionally, it is made step by step as follows:

1. Lime, brick dust (or baked clay pieces), and sand are carefully measured in set ratios.

2. Lime and brick dust are thoroughly mixed in their dry state. This ensures homogeneity and directly impacts final durability.

3. Clean water is gradually added, and the mixture is kneaded until it reaches a paste-like consistency (traditionally, even by foot).

4. The consistency is crucial: it should be neither too runny nor too stiff, but workable. Adjustments can be made depending on the type of application.

5. The prepared mortar is then applied to walls, floors, or plaster surfaces.

Properties and Advantages of Khorasan Mortar

Khorasan mortar possesses both historical and technical advantages that explain its widespread use for centuries. Its key features include:

• Exceptional durability: It hardens over time into a stone-like structure.

• Water resistance: Particularly long-lasting in water-contact structures such as cisterns, baths, aqueducts, and bridges. It preserves integrity even in humid environments.

• Flexibility: It adapts to natural movements of structures, reducing the risk of cracks and maintaining structural integrity.

• Eco-friendly: Made entirely from natural materials, free of chemicals, and allows structures to “breathe,” supporting healthy indoor humidity balance.

• Restoration value: Enables authentic restoration of historical monuments, playing a vital role in preserving cultural heritage.

Types and Applications of Khorasan Mortar

Depending on usage and proportions, Khorasan mortar can be prepared in different types:

• Khorasan Plaster: Used as wall finishing, providing aesthetics and water resistance.

• Khorasan Building Mortar: Functions as a main binder in stone and brick masonry, giving skeletal strength.

• Underground Khorasan Mortar: Specifically designed for cisterns, sewers, and waterways due to high resistance to water and pressure.

• Modern Khorasan Mortar: Traditional formula enhanced with modern additives, providing faster application and controlled performance.

Usage Areas:

• Restoration of historical monuments and landmarks

• Water structures (bridges, aqueducts, baths, cisterns)

• Wall and floor plastering

• Masonry of stone and brick constructions

• Modern engineering projects requiring durable, water-resistant flooring solutions

How to Identify Khorasan Mortar?

To determine whether mortar in a historical building is Khorasan, some visual observations and simple tests can be made:

• It generally has a reddish hue due to brick dust.

• Small brick or clay fragments are visible in its texture.

• Unlike regular lime mortar, it is much harder and does not easily crumble.

• It resists water exposure and retains integrity.

• When scraped with a sharp object, it shows notable resistance rather than easily flaking.

For definitive identification, laboratory analysis by experts is the most reliable method.

Architectural Structures Using Khorasan Mortar

Throughout history, Khorasan mortar has been used in significant architectural masterpieces, offering resistance against water, moisture, and time.

Historical Examples:

• Roman and Byzantine Architecture: Aqueducts, bridges, and massive cisterns showcasing Roman engineering brilliance heavily relied on Khorasan mortar, proving its water resistance.

• Ottoman Architecture: Baths, mosques, complexes, fountains, and water structures were built with this mortar. Examples include the Süleymaniye Mosque, Rumeli Fortress, and Sultanahmet Complex.

• Hagia Sophia: In restoration works, original-like Khorasan mortar has been used to maintain its authentic structure and durability.