Movement Joints in Masonry: Definition, Types, and Placement Requirements

Movement joints are intentional separations built into masonry walls to accommodate the expansion, contraction, and shrinkage that all masonry materials experience over time. Without them, stresses from volume changes have nowhere to dissipate, leading to random cracking that compromises both structural integrity and visual appearance. Understanding where to place these joints — and which type to use for each material — is essential for specifiers, designers, and contractors working with brick or concrete masonry systems.

As required by CSA A371, the detailing, spacing, and location of movement joints must be indicated in contract documents, whether in specifications, drawings, or related technical submittals. This requirement shifts responsibility to the designer to evaluate wall geometry, material properties, and environmental exposure before construction begins.

Why "Movement Joint" Replaced "Control Joint" in Modern Standards

The term "control joint" — which historically indicated detailing to release internal tensile stresses caused by shrinkage — has been phased out of CSA Masonry Standards in favour of the more generic term "movement joint." The Canada Masonry Design Centre defines a movement joint as "a vertical or horizontal separation built into a masonry wall to reduce restraint and the corresponding stresses by accommodating movement of the wall or movement of other structural elements adjacent to the walls."

This broader definition covers both expansion and contraction of masonry, as well as differential movement between the masonry and other parts of the structure. The term is now standard across the CSA suite of standards and the National Building Code of Canada.

Expansion Joints for Clay Brick: Accommodating Irreversible Moisture Expansion

Clay brick expands over its lifetime as it absorbs moisture. This expansion is cumulative and irreversible. Expansion joints leave a continuous, unobstructed gap through the brick wythe, filled with a highly compressible material. As the brickwork expands, the joint partially closes, preventing stress build-up that would otherwise cause cracking.

Project specifications should require sealants to conform to ASTM C920, Grade NS, Use M, with a minimum Class 50 compressibility rating. Silicone sealants are generally recommended for their high elasticity and weather resistance. A circular foam backer rod, sized approximately 25% larger than the joint width, controls sealant depth, provides a surface to tool against, and extends sealant life. Sealant depth should be approximately half the joint width, with a minimum depth specified to ensure adequate movement capacity.

Typical industry recommendations call for vertical expansion joints at spacings ranging from 6.0 m to 7.5 m, significantly tighter than the 12.0 m sometimes seen in older specifications. Expansion joints are also required at corners, wall offsets, junctions with dissimilar materials, and at parapets where thermal cycling is more pronounced.

Control Joints for Concrete Masonry Units: Managing Shrinkage

Unlike clay brick, concrete masonry units (CMU) shrink over time as they dry and cure. Control joints create a vertical plane of weakness so that shrinkage cracking happens at the joint in a straight, predictable line rather than randomly across the wall face. They are sealed with a backer rod and appropriate sealant to keep the joint weathertight while still allowing movement.

Some specifications erroneously call for horizontal reinforcement to run continuously through control joints, effectively restraining the movement the joint is intended to accommodate. This contradicts the fundamental purpose of the joint. Horizontal joint reinforcement should never cross a movement joint.

Similarly, specifying multiple vertical reinforcement bars within a single CMU cell at a control joint location can create conflicts with minimum spacing and position requirements in CSA A371-14 and CSA S304-14. Designers must verify that all reinforcement detailing complies with these standards. Cells containing reinforcement shall be filled with a grout meeting the proportion or property specifications of CSA A179-14.

Common Specification Errors That Restrict Movement

A typical problematic specification might state: "Provide block wall control joint at a maximum spacing of 12.0 meters. Reinforce one cell on either side of joint with 2–15M vertical and fill with concrete. All horizontal reinforcing to run continuous through control joint."

This language raises several issues. First, a maximum spacing of 12.0 m does not provide enough detail to the installer as to the exact locations where movement joints should be placed. Second, the distance of 12.0 m between movement joints is large by most industry standards. Third, running horizontal reinforcement continuously through the joint prevents the wall from moving freely, defeating the joint's purpose.

Placement Recommendations for Vertical Movement Joints

Movement joint locations must be specified by the designer in the contract documents, clearly shown on drawings with dimensions tied to building grid lines or other reference points. Industry guidance suggests placing vertical movement joints at:

For CMU walls, typical spacing ranges from 6.0 m to 7.5 m. For clay brick veneer, similar or slightly wider spacing applies depending on exposure and wall restraint conditions. Tighter spacing may be required in high-exposure environments or where movement is amplified by large temperature swings.

Material Selection and Joint Construction

Elastomeric sealants are preferred for movement joints. Three main types are available: urethanes, silicones, and polysulfides. Each offers high elasticity and strong resistance to weathering. The choice depends on joint width, expected movement, substrate compatibility, and UV exposure.

Proper backer rod installation is critical. The rod should be circular foam, sized about 25% larger than the joint width. This ensures the rod stays in place during sealant application and provides the correct depth-to-width ratio for optimal sealant performance.

Additional types of movement joints include building expansion (isolation) joints, which separate portions of a building to prevent stress transfer between structurally independent sections, and construction joints (cold joints), which are formed where concrete work must stop and resume later. Each serves a distinct function and requires appropriate detailing to maintain structural performance and weathertightness.

For further guidance on managing shrinkage-related issues in concrete and screed systems, see our article on shrinkage crack prevention. Related considerations for sealing systems are covered in our review of Sikaflex sealant technologies.