Construction Joints | Masonry Joints | Control Joints | Expansion Joints in Buildings
Construction Joints | Control Joints | Expansion Joints Provision
Construction movement joints are one of the most misunderstood and unappreciated technical issues in the masonry industry. Joints are used in brickwork to accommodate such movements and to avoid cracking.
Masonry move because of temperature causes brick to expand and contract, moisture movement, and structural loading
Movement of Masonry
Unreinforced wall expands by about one millimeter per meter during the life of the structure.
What are Control Joints?
Control joints are typically used to reduce the occurrence of shrinkage related cracking. They also help control cracks from movements other than shrinkage.
It is continuous vertical joints that permit a masonry wall to move little under pressure without cracking
Control Construction Joint Requirements
When control joints are required, masonry only requires vertical control joints. Walls with adequate horizontal reinforcement may not require control joints. It is required where shrinkage cracking may spoil the appearance of the wall and to limit moisture penetration
Control Joint Locations
Cracking due to volume changes in the masonry due to drying shrinkage or temperature changes are likely to create tension in the masonry that will exceed its tensile capacity. Common locations are;
- At changes in wall height.
- At changes in wall thickness such as a duck chases and pilasters.
- At locations where two or more walls interact
- Above and below movement joints and roofs and floors that bear on a wall.
- Near one or both sides of the door and window openings.
- Height changes of internal wall
NB: Use Reinforcement provided on the above-listed locations provides some type of controls over cracks
Expansion joints are placed in masonry walls to allow room for the wall to expand. Expansion joints will get smaller as masonry products expand, closing the gap.
For that reason, mortar should never be allowed in brick expansion joints
Expansion Joint Details
Leave a gap of 20 millimeters in long lengths, such as in compound walls. This allows independent movements off wall sections. The spacing of such joints depends upon local temperature and systemic conditions.
Common Spacing of Construction Joints
- For a brick wall with a brick foundation 5 to 7 m.
- For a brick wall with a brick foundation and reinforcement 7 to 10 m.
- For brick wall with RCC footing and ground beam 30 m
Cracking Multistory Buildings.
There is differential movement between RCC and masonry. Provide horizontal expansion joints every two storey to allow for such movement.
Joint Filling Material
The material should be compressible by at least 50%. Use baker rods, foam pads, or neoprene pads in vertical joints. Cover such rods with polyurethane joints sealants
It is important that the designer fully considers the movement of brickwork considering the geometry of the building and its orientation. The frequency, location, and width of the joints should be sufficient to accommodate both reversible and irreversible movements.