Masonry Wall Cracks: Causes, Implications, and Remedies

Masonry walls have stood the test of time as a hallmark of durable and aesthetically pleasing construction. However, despite their robustness, they are not immune to the formation of cracks, which can vary from minor surface blemishes to severe structural issues. Understanding the causes, implications, and remedies for cracks in masonry walls is crucial for homeowners, builders, architects, and anyone intrigued by the world of construction. In this extensive exploration, we will delve into the intricate world of masonry wall cracks, extending our knowledge across five major types of cracks, their underlying causes, implications, and comprehensive solutions. This comprehensive guide aims to empower readers with an in-depth understanding of the subject.

The Landscape of Masonry Wall Cracks

Masonry wall cracks can be both fascinating and perplexing. These cracks can occur due to various factors, some of which are interconnected. Let’s embark on a comprehensive journey through the realm of masonry wall cracks, starting with the fundamental causes.

Common Causes of Cracks in Masonry Walls

The structural integrity of masonry walls can be compromised by several factors. A thorough grasp of these causes is essential to diagnose and address masonry wall cracks effectively. The primary causes include:

1. Settlement and Subsidence

Settlement: Settlement takes place when a masonry wall experiences downward pressure from the loads it supports. The weight of the building itself and any additional loads contribute to this phenomenon. While settlement is common in construction, managing it to an infinitesimally low level is crucial.

Subsidence: Subsidence occurs when the earth beneath the foundations is removed. This removal, often due to drainage issues or excavation, causes the foundation to sink. Subsidence is a more severe issue compared to settlement and is challenging to repair.

Connection Between Settlement and Subsidence: Settlement can lead to subsidence when drains connected to a building shear or crack due to settlement. The subsequent leakage can erode the subsoil, exacerbating the issue. Therefore, managing settlement is essential to prevent subsidence.

2. Poor Design, Construction Methods, or Maintenance

In addition to settlement and subsidence, poor design, construction methods, and maintenance practices can contribute to masonry wall cracks. Flaws in the initial design, inadequate construction techniques, and neglect in maintaining the structure can lead to structural issues and the formation of cracks.

With these fundamental causes in mind, we’ll now delve into five major types of masonry wall cracks, dissecting their origins, implications, and recommended remedies in greater detail.

Types of Cracks in Masonry Walls and Their Causes

1. Expansion Cracks in Masonry Wall

Causes of Expansive Cracks

Expansion cracks in masonry walls are primarily a result of temperature and moisture changes. Materials used in masonry construction can undergo initial shrinkage and subsequent expansion and contraction due to environmental variations. This movement gives rise to expansion cracks. While these cracks are often vertical, they may deviate from this path and become stepped.

Implications of Expansion Cracks: Expansion cracks are typically not structurally significant. However, they can allow water to penetrate the cavity in brick-built houses, potentially leading to the deterioration of wall ties. Therefore, addressing these cracks is essential.

Repair of Expansive Cracks: Repairing expansive cracks involves filling the crack with a mastic or sealastic compound. For more severe cases, creating an expansion joint is recommended. In modern construction, expansion joints are often included during the building phase and concealed behind rainwater downpipes.

2. Cracks Above Openings in Masonry Walls

Cracks appearing above openings in masonry walls can be attributed to several specific causes. Let’s examine each of them individually:

Cause-1: Removal of Windows or Doors with Inadequate Propping

The most common cause of cracks above openings is the removal of existing window frames, often to install PVCu windows. When the lintel and brickwork above the opening are not adequately supported during this process, cracks can form.

Implications of Cracks due to Inadequate Propping: Cracks above openings can weaken the structure and potentially lead to the collapse of the brickwork.

Repair of Cracks due to Inadequate Propping: The most effective repair involves resetting the lintel, repointing or rebuilding the brickwork above the opening, and refitting the window. Simply repointing the cracks without addressing the underlying issue is not a long-term solution and may lead to future problems.

Cause-2: Cracks due to Inadequate Bearings

Inadequate bearing of lintels above openings can result in lintel sag and the formation of cracks. The correct overhang (bearing) of the lintels above openings is typically 150mm (6 inches) on each side. When the bearings are insufficient, the lintel may sag and cracks can appear.

Implications of Cracks due to Inadequate Bearings: These cracks can weaken the lintel’s support and may lead to further structural issues.

Repair of Cracks due to Inadequate Bearings: The recommended repair is to replace the lintel. However, temporary repointing may suffice until the window or door is replaced.

Cause-3: Cracks due to Loads Applied above the Opening

Cracks often appear above first-floor lintels when roof purlins are installed directly over window openings. The load imposed on the lintel can be excessive, causing cracks to form.

Implications of Cracks due to Loads Applied above the Opening: The downward pressure can compromise the structural integrity of the lintel and the surrounding masonry.

Repair of Cracks due to Loads Applied above the Opening: Replacement of the lintel is typically recommended. The severity and age of these cracks will determine whether temporary repointing is sufficient until the window is replaced.

Cause-4: Cracks in Masonry Wall due to No Lintels

In some properties, no lintels are provided, and the masonry relies on the window’s timber frame for support. When windows are replaced in such cases, cracks can emerge.

Implications of Cracks in Masonry Wall due to No Lintels: Without proper lintels, the structural integrity of the masonry is compromised, and cracks can develop.

Repair of Cracks in Masonry Wall due to No Lintels: New lintels need to be installed, and the cracks must be repaired to restore the structural integrity of the masonry.

3. Cracks in Masonry Wall due to Tie Failure

Wall ties are crucial components in masonry construction, as they hold the outside skin of brickwork to the inside. However, over time, these ties can deteriorate, leading to structural issues and the formation of cracks.

Implications of Cracks in Masonry Wall due to Tie Failure: Failure of wall ties can lead to the horizontal cracking seen every sixth course in the mortar joints. If left unaddressed, this issue can result in the collapse of the wall.

Repair of Cracks in Masonry Wall due to Tie Failure: Replacement of wall ties is essential. Addressing the cracking and removing the existing ties is recommended.

4. Cracks in Masonry Wall due to Subsidence

Subsidence-related cracks are the most severe and challenging to repair. Subsidence can occur due to a

variety of reasons, including mining activity, leaking underground drainage, tree root activity, soil types, and more. These cracks are often raking cracks, widest at the top or extending from the top to the bottom of the walls.

Implications of Cracks in Masonry Wall due to Subsidence: Subsidence cracks are indicative of a significant problem with the foundations of the house, potentially leading to structural instability.

Repair of Cracks in Masonry Wall due to Subsidence: Addressing subsidence typically involves some form of underpinning. However, due to the complexity of this issue, seeking specialist advice from a structural engineer is essential.

5. Wall Cracks due to Ground Heave

Cracks caused by ground heave share similarities with subsidence cracks but are widest at the base of the wall. Ground heave is often caused by the expansion of clay subsoils, and it can occur due to factors such as weather conditions and the removal of trees.

Implications of Cracks due to Ground Heave: Ground heave can lead to structural instability, and the pattern of these cracks often mirrors those of subsidence cracks.

Repair of Cracks due to Ground Heave: In extreme cases, underpinning and/or deeper foundations may be the only solution. This is a drastic measure and should be considered as a last resort. In cases of ground heave problems, an alternative solution may involve removing as much of the clay from around the foundation as possible and replacing it with hardcore.

Understanding the Implications and Solutions

The Implications of Masonry Wall Cracks

Masonry wall cracks, regardless of their causes, can have various implications for the structural integrity of a building. Understanding these implications is essential for homeowners and professionals alike:

  1. Structural Instability: Cracks in masonry walls can weaken the structural integrity of a building. Depending on the location and severity of the cracks, the stability of the entire structure may be compromised.
  2. Water Infiltration: Cracks can provide pathways for water to enter the masonry, potentially leading to moisture-related issues such as dampness and mold growth. This can further deteriorate the masonry and impact indoor air quality.
  3. Thermal Inefficiency: Gaps in the masonry can allow for heat transfer, resulting in decreased energy efficiency. This can lead to increased heating and cooling costs for the building.
  4. Aesthetic Concerns: Cracks in masonry walls can be unsightly, diminishing the visual appeal of a structure. This is especially relevant for historical or architecturally significant buildings.
  5. Safety Hazards: In cases of severe structural compromise, masonry wall cracks can pose safety hazards to occupants and passersby. Falling debris or structural failure can lead to accidents and injuries.

Solutions for Masonry Wall Cracks

Addressing masonry wall cracks requires a methodical approach that begins with a thorough understanding of the causes and implications. The specific solution depends on the type, severity, and location of the cracks. Here are some general approaches to resolving masonry wall cracks:

  1. Cosmetic Repair: In cases of minor, non-structural cracks, cosmetic repairs can be effective. This involves filling the cracks with suitable materials and then repointing or rendering the affected area to restore its appearance.
  2. Repointing: Repointing involves removing deteriorated mortar and replacing it with new mortar. This is a common repair method for cracks in mortar joints.
  3. Lintel Replacement: When cracks occur above openings due to inadequate propping or bearing, it may be necessary to replace the lintel and, if required, rebuild the brickwork above the opening.
  4. Wall Tie Replacement: In cases of tie failure, replacement of wall ties is crucial. This should be accompanied by the removal of existing, deteriorated ties.
  5. Expansion Joints: For expansive cracks, creating expansion joints is an effective solution. These joints allow for controlled movement and help prevent the recurrence of cracks.
  6. Underpinning: In situations where subsidence or severe ground heave is the cause of cracks, underpinning may be necessary. This involves strengthening the foundation to stabilize the structure.
  7. Structural Engineer Consultation: When dealing with complex or severe cracks, seeking advice from a structural engineer is essential. They can provide a tailored solution based on a thorough assessment of the situation.

Masonry wall cracks are not merely surface blemishes but can signify underlying structural issues. By understanding the diverse causes, implications, and remedies for these cracks, homeowners, builders, architects, and construction enthusiasts can make informed decisions and take appropriate actions. Whether it’s addressing minor cosmetic issues or dealing with severe structural instability, a comprehensive understanding of masonry wall cracks is a valuable asset in ensuring the longevity, safety, and visual appeal of masonry structures. With the right knowledge and expertise, we can preserve and protect these architectural gems for generations to come.

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