Types Of Masonry Wall Systems
August 29th 2024
Types Of Masonry Wall Systems
August 29th 2024
Historic brick masonry, a cornerstone of architectural heritage, is foundational to understanding the evolution of building techniques and materials over time. Historic masonry buildings, typically over 50 years old and of architectural or cultural significance, often present unique challenges that require careful evaluation and restoration. These buildings are integral to our built environment, and their preservation is essential to maintaining the historical fabric of our communities.
Understanding Historic Brick and Mortar
Brick and mortar are the primary components of historic masonry. Brick, a material used for thousands of years, is known for its durability, compressive strength, and thermal mass. Historic bricks were often made locally from natural clays, which were shaped and then fired in kilns. The color, size, and texture of bricks can vary significantly depending on the source of the clay and the firing method, giving each region’s masonry a distinctive character.
Mortar, the binding agent used in brick masonry, is equally important. Historically, mortar was composed primarily of lime, sand, and water, with lime serving as the key ingredient. Lime mortars are softer and more flexible than modern cement-based mortars, allowing the masonry to “breathe.” This breathability is crucial for managing moisture within the wall system, as it permits water vapor to escape, preventing the buildup of moisture that could lead to damage over time.
Masonry Wall Systems
Historic masonry walls are often categorized into four primary types: mass, transitional, curtain/barrier, and cavity wall systems. These systems evolved as builders experimented with materials and techniques to meet the demands of taller and more complex structures.
- Mass Masonry Walls: The oldest and simplest form, mass walls rely on their thickness to bear loads and manage moisture. These walls, made of stone or brick, are solid and typically several feet thick, providing substantial thermal mass. They rely on their large mass to absorb water that inevitably penetrates beyond the exterior face of the wall, which then evaporates over time (Figure 1).
Historic brick masonry, a cornerstone of architectural heritage, is foundational to understanding the evolution of building techniques and materials over time. Historic masonry buildings, typically over 50 years old and of architectural or cultural significance, often present unique challenges that require careful evaluation and restoration. These buildings are integral to our built environment, and their preservation is essential to maintaining the historical fabric of our communities.
Understanding Historic Brick and Mortar
Brick and mortar are the primary components of historic masonry. Brick, a material used for thousands of years, is known for its durability, compressive strength, and thermal mass. Historic bricks were often made locally from natural clays, which were shaped and then fired in kilns. The color, size, and texture of bricks can vary significantly depending on the source of the clay and the firing method, giving each region’s masonry a distinctive character.
Mortar, the binding agent used in brick masonry, is equally important. Historically, mortar was composed primarily of lime, sand, and water, with lime serving as the key ingredient. Lime mortars are softer and more flexible than modern cement-based mortars, allowing the masonry to “breathe.” This breathability is crucial for managing moisture within the wall system, as it permits water vapor to escape, preventing the buildup of moisture that could lead to damage over time.
Masonry Wall Systems
Historic masonry walls are often categorized into four primary types: mass, transitional, curtain/barrier, and cavity wall systems. These systems evolved as builders experimented with materials and techniques to meet the demands of taller and more complex structures.
- Mass Masonry Walls: The oldest and simplest form, mass walls rely on their thickness to bear loads and manage moisture. These walls, made of stone or brick, are solid and typically several feet thick, providing substantial thermal mass. They rely on their large mass to absorb water that inevitably penetrates beyond the exterior face of the wall, which then evaporates over time (Figure 1).
Figure 1: Overview of how a mass masonry wall sheds water. Illustrations on this page courtesy of Holland/Niezelski
2. Transitional Masonry Walls: Emerging in the late 19th and early 20th centuries, transitional walls mark a shift from mass masonry to steel-framed buildings. These walls incorporate both masonry and steel, allowing for taller structures with thinner walls. However, the introduction of steel led to challenges in managing moisture and thermal movement, as the two materials behave differently.
2. Transitional Masonry Walls: Emerging in the late 19th and early 20th centuries, transitional walls mark a shift from mass masonry to steel-framed buildings. These walls incorporate both masonry and steel, allowing for taller structures with thinner walls. However, the introduction of steel led to challenges in managing moisture and thermal movement, as the two materials behave differently.
Figure 2: Overview of how a cavity wall sheds water. Illustrations on this page courtesy of Holland/Niezelski
3. Curtain/Barrier Walls: These walls use masonry as a non-load-bearing cladding system attached to a steel or concrete structure. The masonry serves primarily as an aesthetic facade, and the wall’s ability to manage water relies heavily on the integrity of the exterior surface, as water infiltration can lead to significant damage.
4. Cavity Walls: Cavity walls incorporate an air space between the outer masonry cladding and the inner structure, which helps manage water penetration. The air space allows water to drain away, while modern systems include flashing and weep holes to further enhance water management.
3. Curtain/Barrier Walls: These walls use masonry as a non-load-bearing cladding system attached to a steel or concrete structure. The masonry serves primarily as an aesthetic facade, and the wall’s ability to manage water relies heavily on the integrity of the exterior surface, as water infiltration can lead to significant damage.
4. Cavity Walls: Cavity walls incorporate an air space between the outer masonry cladding and the inner structure, which helps manage water penetration. The air space allows water to drain away, while modern systems include flashing and weep holes to further enhance water management.
Figure 3: Overview of how a cavity wall sheds water. Illustrations on this page courtesy of Holland/Niezelski
Restoration and Repair
Restoring historic brick masonry requires a comprehensive understanding of the materials and techniques used in the original construction. The first step in any restoration project is a visual condition assessment to identify distress and understand the root causes of deterioration. This assessment should consider the building’s historical context, including any previous repairs that may have altered the original materials.
Repair techniques must be carefully chosen to ensure compatibility with the historic materials. For example, using a modern Portland cement-based mortar in a historic building can lead to damage, as it is harder and less flexible than traditional lime mortar. Such incompatibility can cause cracking, spalling, and other forms of deterioration. Therefore, it is crucial to match the repair materials in terms of compressive strength, density, and vapor permeability to the original materials.
The preservation of historic masonry is about maintaining the aesthetic value of old buildings and understanding and respecting the historic materials and construction techniques. By recognizing the fundamental properties of brick and mortar, and the specific challenges posed by different masonry wall systems, appropriate restoration strategies can be developed that ensure the longevity of historic structures.
Restoration and Repair
Restoring historic brick masonry requires a comprehensive understanding of the materials and techniques used in the original construction. The first step in any restoration project is a visual condition assessment to identify distress and understand the root causes of deterioration. This assessment should consider the building’s historical context, including any previous repairs that may have altered the original materials.
Repair techniques must be carefully chosen to ensure compatibility with the historic materials. For example, using a modern Portland cement-based mortar in a historic building can lead to damage, as it is harder and less flexible than traditional lime mortar. Such incompatibility can cause cracking, spalling, and other forms of deterioration. Therefore, it is crucial to match the repair materials in terms of compressive strength, density, and vapor permeability to the original materials.
The preservation of historic masonry is about maintaining the aesthetic value of old buildings and understanding and respecting the historic materials and construction techniques. By recognizing the fundamental properties of brick and mortar, and the specific challenges posed by different masonry wall systems, appropriate restoration strategies can be developed that ensure the longevity of historic structures.
Written by Reba Ashby
A historic preservationist specializing in traditional masonry, architectural conservation, and building assessments.