Masonry walls in buildings can develop different types of cracks, ranging from minor and insignificant ones to those that require costly repairs, and even those that necessitate the complete demolition of the wall. One of the primary reasons for such cracks is the movement of the building, which results in settlement and subsidence.
The cracks that appear in masonry walls can be indicative of the degree of damage caused by the movement of the building. In some cases, these cracks may be barely visible and may not pose a significant threat to the structural integrity of the wall. However, in other cases, the cracks can be extensive, and if left unaddressed, they can lead to more severe damage to the wall and the building as a whole.
It is essential to identify the causes of these cracks and address them appropriately to prevent further damage. The movement of the building causing settlement and subsidence is one of the primary causes, but there can be other factors as well. Some of these factors include changes in temperature and humidity, soil erosion, and inadequate construction practices.
The repair of cracks in masonry walls can range from simple patching to more complex interventions, such as the installation of reinforcement systems or even the complete rebuilding of the wall. The choice of repair method depends on the severity of the damage, the cause of the crack, and the budget available for repairs. However, it is crucial to address these issues promptly to prevent further damage to the building and ensure the safety of its occupants.
Common Causes of Cracks in Masonry Walls
The figure provided depicts the settlement and subsidence of building walls. It is clear from the image that the walls have experienced a significant amount of settling, causing them to sink lower into the ground. This settling has also caused the walls to become uneven, with some sections appearing to be more affected than others.
Subsidence can occur for a variety of reasons, including changes in soil moisture levels and soil compaction. In some cases, subsidence can be the result of the natural settling of the soil over time, while in other cases, it may be caused by human activities such as construction or excavation.
Settlement and subsidence can have serious consequences for buildings, including structural damage and even collapse. It is important for building owners and managers to be aware of the signs of settling and subsidence and to take appropriate action to address these issues. This may include repairing or reinforcing the affected walls, as well as taking steps to prevent further settling in the future.
Fig.1: Settlement and Subsidence of Masonry Wall
Masonry walls can experience two types of structural issues: settlement and subsidence. Settlement occurs due to the downward pressure of loads on the wall, while subsidence is caused by the removal of earth from beneath the building’s foundation. While settlement can usually be addressed through simple cosmetic repairs, subsidence can be a costly and challenging problem to fix.
In some cases, settlement of walls can lead to subsidence. For example, if the drains connected to a building become damaged due to settlement, subsequent leakage can wash away the subsoil and cause subsidence. All buildings settle to some degree when they are first constructed, but the goal is to keep this settlement at a very low level.
Movement and cracking in masonry walls can also be caused by poor design, construction methods, or maintenance. The diagrams in this context show brickwork, but similar cracks can form in stonework. To ensure the longevity and safety of a building, it is important to address any structural issues promptly and properly.
Fig.2: Cracks in Masonry Walls
Types of Cracks in Masonry Walls and Causes
1. Expansion Cracks in Masonry Wall
Causes of Expansive Cracks
Walls can be impacted by various environmental factors such as temperature and moisture changes. As a result, the materials used in constructing the walls may undergo initial shrinkage or subsequent expansion and contraction. Such movement can lead to the formation of expansion cracks in masonry walls. Although these cracks are often vertical, they can sometimes follow the path of least resistance and end up stepped.
Vertical cracks are commonly observed, but the direction of the crack is not always straightforward. When a crack follows the line of least resistance, it may result in a stepped crack. This phenomenon occurs when the crack changes direction as it progresses through the wall, forming a series of steps. In such cases, the severity of the crack can be influenced by the properties of the materials used in the construction of the wall, the environmental conditions, and the age of the building. Therefore, it is crucial to identify the underlying causes of wall cracks to determine the best repair and maintenance approach.
Fig.3: Expansion Cracks in Masonry Wall
When it comes to cracks in buildings, there is a specific type that is commonly observed above window and door openings. These cracks tend to appear due to the relief provided by the opening itself, and they often have a consistent width. This particular characteristic is what sets them apart from other more severe types of cracks that can occur in structures. Despite their presence, these cracks are generally not considered to be as serious as others that can compromise the stability of a building.
Repair of Expansive Cracks
Paragraph 1: An expansive crack is not considered to be a significant problem in terms of the structural integrity of a building. However, it can allow water to penetrate into the cavity of brick-built houses and lead to the deterioration of the wall ties over time. To prevent this from happening, it is recommended to fill the crack with a mastic or sealastic compound.
Paragraph 2: For more severe cracking, it is advisable to create an expansion joint. This involves cutting a joint into the wall and filling it with a compressible material that has a waterproof stopper on the outside. By doing this, any further movement in the wall can be accommodated without causing any additional damage. In some modern buildings, expansion joints are created during the construction process and are hidden behind rainwater downpipes.
Overall, it is important to address any cracks in a building’s walls to prevent water from penetrating and causing further damage. While smaller cracks can be filled with a mastic or sealastic compound, larger cracks may require the creation of an expansion joint. Taking these steps can help ensure the long-term stability and safety of the building.
2. Cracks Above Openings in Masonry Walls
Causes
Cracks above openings in masonry walls can have various causes. One of these causes is the removal of windows or doors without adequate propping. When a window or door is removed, it can create an unsupported span of masonry above the opening. If the weight of the masonry is not adequately supported during the removal process, cracks can occur.
Another cause of cracks above openings in masonry walls is inadequate bearings. The bearing is the surface upon which a load rests. If the load is not adequately distributed across the bearing surface, the masonry above the opening can crack. This can happen if the bearing surface is too small or if the load is not evenly distributed across the surface.
A third cause of cracks above openings in masonry walls is when loads are applied directly over the opening. This can occur when heavy objects are placed on top of the masonry above the opening, causing it to crack. For example, if someone were to place a large flower pot on top of the masonry above a window, the weight of the pot could cause the masonry to crack.
Lastly, the absence of lintels can also be a cause of cracks above openings in masonry walls. Lintels are horizontal beams that span the opening and provide support for the masonry above. Without a lintel, the weight of the masonry above the opening is not adequately supported, which can lead to cracking.
Cause-1: Removal of windows or doors with inadequate propping
One of the most frequent causes of cracks in walls can be attributed to the replacement of old window frames with PVCu ones. The process of removing the existing window frames can cause stress to the surrounding walls, resulting in cracks. These cracks may appear immediately after the installation or can develop over time due to changes in temperature and humidity levels.
When a window frame is removed, it creates an empty space that needs to be filled with the new PVCu frame. This can require cutting away part of the wall to create the necessary space. Such alterations can cause structural weakness in the surrounding area, making it more susceptible to cracking.
Moreover, the installation of PVCu window frames can also impact the overall weight distribution of the wall. The new frames may be lighter than the old ones, and the difference in weight distribution can put additional stress on the walls. This can lead to the formation of cracks, which may not be visible immediately but can develop over time.
Therefore, it is essential to take the necessary precautions when installing new window frames to prevent cracks from occurring. This can involve using a professional installation service that has experience working with PVCu frames and taking steps to reinforce the surrounding walls before installation. Additionally, regular inspection and maintenance of the frames can help identify any issues early and prevent further damage to the walls.
Repair of Cracks
The recommended course of action for repairing a damaged lintel and brickwork above a window is to reset the lintel, rebuild the brickwork, and refit the window. This approach ensures that the structure is properly restored and can withstand any future changes or stresses.
On the other hand, a poor repair option is to merely repoint the cracks in the brickwork without addressing the underlying issue. This approach is inadequate because the brickwork would still be resting on the new window frame. As a result, the brickwork above the opening may eventually collapse when the window needs to be replaced again.
It’s important to prioritize a thorough and effective repair solution when dealing with issues like damaged lintels and brickwork. Failing to address the underlying problem could result in further damage and potentially costly repairs down the line.
Cause-2: Cracks due to Inadequate Bearings
Lintels are an essential component of building construction that provide support for the structure above openings such as doors and windows. To ensure the proper function of a lintel, it is crucial to have the correct overhang or bearing on both sides of the opening. The recommended overhang for lintels is 150mm or 6 inches on each side.
If the bearings are inadequate or not in accordance with the recommended standards, the lintel may drop and cause cracks to appear. This can compromise the structural integrity of the building and pose a safety hazard. It is therefore essential to adhere to the recommended bearing standards when installing lintels to ensure the stability and longevity of the structure.
Repair of Cracks due to Inadequate Bearing
The recommendation is to replace the lintel, but in the meantime, repointing will be enough until a window or door replacement takes place.
Cause-3:Cracks due to loads applied above the opening
The cracking of walls above first floor lintels is a common occurrence that can be attributed to the installation of roof purlins directly above the window openings. The weight of these purlins creates a load that is too much for the lintel to bear, resulting in the downward pressure that causes the cracking. This phenomenon is a result of structural limitations that can be addressed through the use of alternative support systems or more robust lintels. Properly addressing this issue can prevent further damage to the building and ensure its longevity.
Repair
The recommendation has been made once again to replace the lintel. The extent and age of the cracks will determine whether a simple repointing job would be sufficient until the window replacement takes place.
Cause-4: Cracks in Masonry Wall due to No Lintels
There are certain properties where lintels are not installed, and instead, the weight of the masonry above the window is supported by the timber frame of the window itself. However, when the window is replaced, cracks tend to appear in the masonry.
This phenomenon occurs because the timber frame of the original window was able to distribute the weight of the masonry above evenly. But when the window is replaced, the new frame might not be strong enough to support the same weight, leading to cracks in the masonry.
It is important to note that the absence of lintels in such properties is not necessarily a design flaw, but rather a conscious decision based on certain aesthetic or structural considerations. Nonetheless, it is crucial to ensure that any new window frame can support the weight of the masonry above, in order to prevent any damage or structural issues.
Repair
There are two tasks that need to be completed: installing new lintels and repairing cracks. The lintels are yet to be installed and the existing ones need to be replaced. As for the cracks, they require repair work to be carried out.
3. Cracks in Masonry Wall due to Tie Failure
Wall ties are an essential component of solid and cavity walls built in stretcher bond. They are made of metal and serve the purpose of holding the outside skin of brickwork to the inside. However, over time, these ties may experience failure due to rust. The rusting of the metal ties causes them to expand, which in turn leads to cracking typically visible every sixth course horizontally in the mortar joints. This cracking can be a cause for concern and requires attention to prevent further damage.
Repair
Paragraph 1: Replacement wall ties are crucial for maintaining the integrity of a building’s walls. These ties serve to keep the bricks or blocks in place and prevent them from shifting or separating over time. Without proper wall ties, the structure is at risk of collapse, which can pose a serious danger to occupants and passersby.
Paragraph 2: Cracking is an early warning sign that the wall ties may be failing. This can occur when the ties corrode or degrade over time, causing the walls to shift or bow outward. If left unchecked, the cracking can worsen, leading to more severe structural damage and an increased risk of collapse.
Paragraph 3: To address this issue, it is recommended to remove the existing wall ties and repoint the affected areas. Repointing involves removing and replacing the damaged mortar joints between the bricks or blocks. This process helps to restore the strength and stability of the walls, allowing them to withstand the forces of nature and time. By replacing the old wall ties with new ones, the building can continue to stand strong for many years to come.
4. Cracks in Masonry Wall due to Subsidence
Masonry walls can suffer from severe and troublesome cracks caused by subsidence, which is a serious problem that is difficult to repair. The underlying cause of subsidence can vary greatly, such as mining activity, underground drainage leaks, tree root activity, and different types of subsoil including peak subsoil, clay subsoil, and running sand. Nevertheless, the fundamental issue is the same – the house’s foundations are shifting, leading to a host of issues.
Typically, cracks are the first sign of trouble, and they can take on the form of raking cracks that are widest at the top. These cracks can appear at the building’s corners or span from the top to the bottom of the walls. The list of causes for subsidence is long, but the outcome is consistent – foundation instability that requires prompt attention.
Repair of Cracks due to Subsidence
To carry out this task, it will usually be necessary to provide some kind of support structure. However, it is essential to seek guidance from a structural engineer with expertise in this area.
5. Wall Cracks due to Ground Heave
The widening crack at the base of a wall is similar in appearance to a subsidence crack, but it may be caused by ground heave. The main culprit behind ground heave is the expansion of clay subsoils, which can occur due to changes in weather conditions. When clay becomes waterlogged, it can expand and push up foundations, leading to the formation of cracks. In older buildings with shallow foundations, this phenomenon is particularly common.
Ground heave can also be triggered by the removal of trees, which is why caution is necessary when taking down trees close to a property. Ideally, the process should be spread out over a period of several years, to allow for gradual ground movement. By taking this approach, it is possible to mitigate the risk of ground heave, which can have a detrimental impact on the structural integrity of a building over time. As such, it is important to be aware of the potential causes of ground heave and take proactive steps to prevent it from occurring.
Repair of Cracks due to Ground Heave
When facing extreme cases of foundation problems, it may be necessary to consider drastic measures such as underpinning or installing deeper foundations. These solutions can be costly and disruptive, but they may be the only effective way to address the issue.
One specific problem that can require attention is ground heave. This occurs when clay around the foundation swells and pushes against the structure, causing damage. To address this problem, it is necessary to remove as much of the clay as possible from around the foundation and replace it with a more stable material such as hardcore. This can help to alleviate the pressure on the foundation and prevent further damage from occurring.