Vibing Masonry #4: The Durable Resilience of Masonry Architecture Over the Centuries

Words: Steve Blye

As a design architect for four decades, I've long recognized masonry (clay brick, concrete masonry units, stone, and manufactured stone) as a superior, durable building material. Stone, clay bricks, and CMUs are renowned for their toughness, effectively resisting physical stresses due to their unique chemical compositions and physical properties. These materials withstand erosion, extreme weather, and physical attacks, including fires and blasts, due to their unique micro-components and chemical/physical characteristics.

Masonry assemblies, typically held together by mortar, offer exceptional compressive strength, preventing collapse under heavy loads and resisting powerful lateral forces like hurricane winds and storm waves. Design enhancements such as increased wall thickness, reinforcement, and strategic bonding patterns (e.g., brick coursing) further bolster their resistance to high-energy impacts, making them ideal for protective structures. Numerous interlocking stone walls have even survived millennia without mortar bonding.

Historically, masonry walls served dual roles as both structure and exterior protection. These walls, often several feet thick, repelled vast quantities of water while absorbing moisture and gradually releasing it as vapor to prevent interior penetration. Roof overhangs and cornices directed rain away from the building's surface, enhancing water resistance and minimizing freeze/thaw cycle damage.

Construction techniques, developed through trial and error since ancient times (e.g., columns, lintels, gables, arches, vaults, and buttresses), distributed weight and resisted external forces while allowing window openings for daylighting and ventilation. Roofs constructed with slate or clay tiles shed water and resisted rot, protecting the stone arched vaults or timber-framed roof structures beneath.

Key features contributing to masonry's durability include:

  1. Thermal Mass: Masonry's significant mass helps regulate indoor temperatures by storing and slowly releasing heat, increasing energy efficiency.
  2. Fire Resistance: Materials like stone, brick, and concrete masonry units (CMUs) are highly fire-resistant, providing long-term protection against damage.
  3. Low Maintenance: Masonry requires minimal upkeep, as its materials resist decay, pests, rot, and salt, unlike wood, metal, plasterwork, and petroleum-based materials.
The Resilience of Natural Stone Masonry

Future articles will explore advancements in construction techniques that enhance building and city resilience. Building stones, including igneous, sedimentary, and metamorphic types, have varying strength properties.

Granite and quartz, known for their durability, are excellent choices for harsh environments. Granite, composed primarily of quartz, feldspar, and mica, is dense, hard, and has low porosity, preventing water and salt ingress. Its interlocking crystal structure resists abrasion and chemical breakdown, including salt corrosion. Quartz, a mineral made of silicon dioxide (SiO2), is exceptionally hard and chemically stable, resisting water and salt penetration. These properties make granite and quartz ideal for environments exposed to salt. Porous limestone and sandstone walls often have granite or quartz at their bases to withstand freeze/thaw cycles and snow-melting salts.

Next, we will focus on the actual chemical and physical properties that allow water-soluble mud or clay and manufactured concrete to be transformed into brick and block building materials that rival stone for its strength, durability, and resilience over time.

The Resilience of Clay Brick Masonry

The earliest bricks, dating to around 7,000 BC in Turkey, were made from mud clay mixed with straw, shaped by hand, and sundried. Native Americans used similar techniques, covering brick joints with mud. During the Medieval period, workers kneaded clay by hand, placed it in wooden molds, and air-dried it. However, cold and wet climates led to the evolution of firing bricks in kilns, enhancing their durability and water resistance.



In China, bricks dating back to at least 4400 BCE were baked in kilns at over 1,100°F, primarily used as flooring. Fired brick, made from sand, iron oxide, clay, lime, and magnesia, is among the longest-lasting forms of brick. The Romans pioneered mobile kilns, enabling remote brick production for public works and military fortifications. By the Renaissance, brick buildings were common throughout Europe, including brick Gothic cathedrals.



During the Industrial Revolution in Great Britain, brick manufacturing used red clay, naturally colored by the mineral iron oxide. Red bricks were less expensive than cut stone and easier to see in dense fog, aiding travelers.

Key Features of Clay Brick Masonry:

  1. Material Properties: Clay bricks have low water absorption and strong resistance to freeze-thaw cycles, safeguarding against water and saltwater corrosion.
  2. Design and Construction:
              - Drainage Wall Systems: Incorporate cavity or anchored veneer walls with air spaces that redirect moisture to weep holes, facilitating drainage.
              - Barrier Wall Systems: Rely on thick masonry and mortar to minimize moisture penetration, retaining moisture until it evaporates.
  3. Preventive Measures: Flashing, sealants, and water-resistant barriers prevent water ingress through joints.
The composition of clay, with fine-grained minerals like kaolinite and illite, provides plasticity when wet and hardness when fired. The vitrification process, occurring above 1,000°C, melts clay particles into a dense, glass-like structure, reducing porosity, enhancing mechanical strength, and improving water resistance. This vitrified nature is crucial for areas with freeze-thaw cycles and saltwater exposure, making clay brick masonry ideal for coastal settings.





The Resilience of Concrete Masonry Units

Concrete masonry units (CMUs) are designed to withstand environmental challenges like water pressure and saltwater exposure. Their durability stems from their chemical processes, mechanical properties, and thoughtful design.



  1. Chemical Composition and Processes:
              -     Cement Hydration: This process involves the hydration of Portland cement, bonding aggregates and strengthening concrete.
    - Carbonation: Atmospheric CO2 reacts with calcium hydroxide in concrete to form calcium carbonate, improving compressive strength and water resistance. Current                         research aims to enhance this process for carbon sequestration.
  2. Mechanical Properties and Design:
              -     Density and Porosity: Proper mix proportioning and well-graded aggregates minimize porosity, making concrete resistant to water and salt penetration.
    - Additives and Treatments: Chemical admixtures like water proofers and silica fume (byproduct of silicon production) enhance concrete's resistance to water and freeze-                thaw pressure.
    - Reinforcement and Design: Steel reinforcement with surface coatings and sealants, improves water resistance, especially in marine environments.


The Resilience of Masonry Mortar

Mortar is crucial for bonding materials like clay bricks and CMUs, enhancing their resilience against environmental and mechanical stress:

  1. Chemical Composition: Mortar consists of cement, lime, sand, and water. Cement provides binding, while lime improves workability, water retention, and permeability, supporting self-healing and resisting chemical degradation, especially in saltwater settings.
  2. Physical Properties: Mortar's adhesion and flexural bond strength keep bricks and blocks intact under stress and exposure. Its moisture resistance is crucial for durability in high-salinity areas.
  3. Resistance to Mechanical Stress: Mortar absorbs and distributes mechanical loads, helping masonry withstand impacts or blasts without compromising its bond.
  4. Construction Integrity: Proper mortar application prevents moisture penetration and ensures structural integrity.
In summary, the combination of masonry materials and techniques ensures long-lasting structural integrity, adapting to environmental and mechanical challenges over centuries. Masonry's strength, thermal efficiency, and minimal maintenance make it integral to our built environment, contributing to the resilience and aesthetic appeal of cities worldwide. Cities rich in historical architecture, like Venice (1500-plus-years-old), exemplify masonry's longevity, with buildings resisting climatic forces and foundation challenges for centuries.




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