Movement Joints
Movement joints are used to allow dimensional changes in masonry and to minimize random wall cracks and other distress. There are various types of movement joints in buildings: expansion joints, control joints, building expansion joints and construction joints. Each type of movement joint is designed to perform a specific task and should not be used interchangeably.
An expansion joint is used to separate brick masonry into segments to prevent cracking due to changes in temperature, moisture expansion, elastic deformation due to loads, and creep. Expansion joints may be horizontal or vertical. The joints are formed of highly elastic materials placed in a continuous, unobstructed opening through the brick wythe – brick expansion joints must be free and clear of all obstructions (such as mortar) to function properly. This allows the joints to close as a result of an increase in size of the brickwork. Expansion joints must be located so that the structural integrity of the brick masonry is not compromised.
A control joint is used in concrete or concrete masonry to create a plane of weakness which, used in conjunction with reinforcement or joint reinforcement, controls the location of cracks due to volume changes resulting from shrinkage and creep. A control joint is usually a vertical opening through the concrete masonry wythe and may be formed of inelastic materials. A control joint will open rather than close. Control joints must be located so that the structural integrity of the concrete masonry is not affected.
A building expansion (isolation) joint is used to separate a building into discrete sections so that stresses developed in one section will not affect the integrity of the entire structure. The isolation joint is a through-the-building joint.
A construction joint (cold joint) is used primarily in concrete construction where construction work is interrupted. Construction joints are located where they will least impair the strength of the structures.
