Where Do You Put Control Joints in Masonry
Control joints in masonry are placed in areas where volume changes may lead to tension that exceeds the masonry’s tensile capacity.
These joints should be located at changes in wall height, changes in wall thickness, movement joints in foundations, floors, and roofs, near door and window openings, and adjacent to corners of walls.
For openings up to 6 ft in width, a control joint should be placed at one side of the opening.
If the opening is larger than 6 ft, control joints should be constructed on both sides when using a slip plane under the bond beam.
Control joints should be sealed with caulking or sealant, approximately half the width of the joint.
Did You Know?
1. Did you know that in masonry, control joints are strategically placed to control cracking? These joints are created by intentionally introducing gaps or separating masonry units at specific locations to minimize the effect of natural expansion and contraction.
2. Unlike popular belief, control joints in masonry are not purely aesthetic but serve an important purpose. Without control joints, the natural forces of expansion and contraction in the masonry can lead to damage such as unsightly cracks, bulging, or even structural failure.
3. The ideal placement of control joints in masonry is determined by factors such as the type of material used, the wall’s height and length, the geographical location, and the anticipated temperature variations. Masonry professionals often employ mathematical calculations and engineering principles to determine the optimal locations for these joints.
4. Control joints are usually filled with a flexible material called joint sealant. This sealant helps accommodate the movement of the masonry while maintaining the joint’s integrity and preventing moisture penetration. The type of sealant used depends on factors like climate conditions, intended usage, and the type of masonry.
5. In addition to controlling cracking, control joints in masonry also play a role in enhancing the overall aesthetic appeal of the structure. By strategically planning the placement and design of these joints, architects and masons can create visually pleasing patterns and give the impression of deliberate detailing in the final construction.
Importance And Purpose Of Control Joints In Masonry
Control joints are crucial in masonry construction as they mitigate the impact of horizontal tensile stresses caused by shrinkage. Masonry materials, such as bricks or concrete blocks, tend to shrink as they cure and dry over time. This shrinkage can create tension within the wall, leading to the development of cracks or even structural damage if not addressed properly.
The primary function of control joints is to create intentional vertical planes of weakness within the wall. This enables the wall to relieve the horizontal tensile stresses. By strategically placing control joints, masonry walls can better withstand the natural shrinkage of the materials. These joints serve as predetermined areas of flexion, allowing the wall to expand and contract without excessively straining the masonry units.
Moreover, control joints prevent aesthetic concerns and limit moisture or air infiltration. Exposed above-grade walls are particularly susceptible to shrinkage cracking, which compromises the visual appeal of the structure. By incorporating control joints at appropriate locations, potential cracking is minimized, thus preserving the wall’s appearance and integrity. Furthermore, these joints act as barriers against moisture and air penetration, enhancing the overall durability of the masonry construction.
Placement Guidelines For Control Joints In Masonry Walls
The placement of control joints in masonry walls is crucial to ensure their effectiveness in relieving tension and preventing aesthetic concerns. Several guidelines and considerations should be followed when determining the ideal locations for control joints.
One fundamental principle is to position control joints where volume changes in the masonry may cause tension exceeding its tensile capacity. This includes areas such as changes in wall height or thickness, as well as movement joints in foundations, floors, roofs, near door and window openings, and adjacent to corners of walls. Identifying these potential trouble spots allows for the strategic placement of control joints, which can effectively absorb the resulting tension.
Another aspect to consider is the size of openings within the wall. For openings up to 6 feet in width, a control joint should be placed at one side of the opening. However, for larger openings, control joints should be constructed on both sides when a slip plane under the bond beam is used. This ensures that the strain resulting from the differential movement around openings is effectively addressed.
Furthermore, control joints should be created on both sides of openings larger than 6 feet when the wall contains vertical reinforcement. Reinforcing the cells adjacent to the opening provides additional support for the jambs, reducing the risk of structural issues.
Control Joints At Various Locations In A Masonry Wall
Control joints play a vital role in maintaining the performance of masonry walls. They can be strategically placed in various locations, considering certain placement guidelines. In specific situations, additional considerations should be taken into account:
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Horizontal joint reinforcement: To resist lateral movement, it is advised to place horizontal joint reinforcement at the lintel bearing location and two courses below. This reinforcement strengthens the wall by minimizing horizontal displacement.
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Load transfer across control joints: Smooth dowels can be used for load transfer. These dowels span the control joints and provide a solid connection between masonry units, allowing independent movement without compromising structural integrity. This ensures efficient load transfer within the wall.
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Special unit shapes: Introducing special unit shapes can serve multiple purposes. These units can provide fire-rated control joints and facilitate out-of-plane load transfer. Designed to meet building code requirements, they offer enhanced fire resistance and improved load distribution capabilities.
Additionally, it is important to note that proper installation of control joints is essential for their optimal functioning and efficacy.
Remember to follow the guidelines recommended by industry standards and consult with professionals when necessary.
Considerations For Reinforcement At Control Joints
Reinforcement at Control Joints: Ensuring Structural Stability and Longevity
Reinforcement at control joints is an essential element for guaranteeing the structural stability and longevity of masonry walls. However, it is important to understand that the type of reinforcement required may vary based on its purpose and location.
One crucial point to consider is that nonstructural reinforcement should not be continuous through control joints. This is done to allow for horizontal movement within the joints and to prevent the introduction of unnecessary stress. On the other hand, structural reinforcement must be continuous to provide the necessary support and integrity to the masonry wall.
In the case of walls that contain vertical reinforcement, it is imperative to reinforce the cell adjacent to the opening. This additional reinforcement plays a crucial role in distributing forces and preventing concentrated stress points. By reinforcing these critical areas, the risk of structural failure or cracking is significantly reduced.
To summarize:
- Nonstructural reinforcement should not be continuous through control joints to allow for horizontal movement and prevent unnecessary stress.
- Structural reinforcement should be continuous to provide the necessary support and integrity to the masonry wall.
- Reinforcing the cell adjacent to wall openings is essential for distributing forces and minimizing stress points.
Sealing And Special Unit Shapes For Control Joints
To ensure the effectiveness of control joints in preventing moisture and air infiltration, it is essential to seal them appropriately. Control joints should be sealed with caulking or other suitable sealants, with a depth approximately half the joint width. This sealant helps create an impermeable barrier, preventing the passage of moisture and air through the joints. Regular inspections and maintenance of the seals are necessary to ensure their continued effectiveness.
In certain cases, special unit shapes can be utilized to enhance the performance of control joints. These specialized units are designed to meet specific requirements, such as fire-rated joints or out-of-plane load transfer. By incorporating these special unit shapes, masonry walls can achieve enhanced fire resistance and improved load distribution, further bolstering their structural integrity.
Note: Control joints play a vital role in masonry construction by relieving horizontal tensile stresses caused by shrinkage, minimizing aesthetic cracking, and limiting moisture or air infiltration.
- Strategic placement
- Appropriate reinforcement
- Proper sealing
- Use of special unit shapes
This comprehensive approach ensures that control joints effectively maintain the stability and longevity of masonry walls. The careful consideration and adherence to guidelines in placing control joints ensure the structural reliability and aesthetic appeal of masonry constructions.
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Frequently Asked Questions
Where are control joints located?
Control joints are typically located every floor over the windows in order to mitigate the effects of temperature and moisture changes. Alternatively, they can also be positioned at every floor line with loose lintels over the windows. If a larger spacing between control joints is desired, such as every two floors, the size of the shelf angle and the width of the joint would need to be increased to accommodate the additional stress and movement. Ultimately, the placement of control joints is crucial to ensure the structural integrity and longevity of the building.
Where should movement joints be located in masonry walls?
Movement joints in masonry walls should be strategically placed between window and door openings to allow for potential movement. These joints should span the full height of the masonry wall to effectively accommodate any structural shifts. It is important, however, to avoid placing movement joints through the openings themselves. This is because continuing the joint between the frames and masonry, as well as around the ends of the lintels, can pose challenges. By positioning the movement joints in the appropriate locations, the stability and longevity of the masonry walls can be maintained while ensuring that any potential movement is properly accounted for.
What is a control joint in a masonry wall?
A control joint in a masonry wall is a strategic vertical joint that helps prevent cracking due to shrinkage. It is filled with mortar, but the inclusion of a bond breaker on one side ensures that no tensile stress can develop across the joint. Without control joints, the natural shrinkage of the wall over time may lead to cracks in the concrete masonry. These joints are an essential measure to maintain the structural integrity and longevity of the wall.
When should you use control joints in concrete?
Control joints should be used in concrete when dealing with unreinforced and lightly reinforced slabs-on-ground to reduce the occurrence of random cracking. These joints create weakened planes within the concrete, allowing for controlled and predetermined cracking locations. By strategically placing control joints, the concrete effectively manages the stress and movement caused by contraction, ensuring minimal cracking and maintaining the integrity and appearance of the slab. Therefore, implementing control joints is essential for ensuring the longevity and durability of such concrete structures.
