How Masonry Control Joints Manage Wall Movement

Concrete masonry units can shrink as they dry. If a long wall is restrained, tensile stress may form and produce cracks at an uncontrolled location. A control joint creates a deliberate plane where movement can be accommodated so cracking is more likely to occur at a planned, detailed location.

A joint is a designed movement detail

The joint typically interrupts or reduces the continuity of the masonry wythe and uses a sealant or other detail to manage weather exposure while allowing movement. It is not merely a cosmetic groove. Reinforcement, bond beams, lintels, wall ties, and intersecting walls affect whether a proposed location will function as intended. The designer’s drawings and specifications determine the joint layout and details.

Coordinate joints with openings and loads

Door and window openings create stress concentrations. Joint placement near openings may help control cracking, but a joint cannot be moved casually if it would interrupt required reinforcement or undermine load transfer. A control joint may affect lateral resistance, fire or acoustic continuity, flashing, and finish work. The contractor should coordinate the masonry details with structural and architectural documents before laying units.

Do not confuse control and expansion joints

Both accommodate movement, but they are not interchangeable terms. In concrete masonry, control joints are commonly associated with shrinkage in the wall. Expansion joints are used to accommodate expansion or movement between building segments and may be detailed differently. The material, movement type, and design determine which detail is appropriate.

Field checks

• Confirm joint locations against the approved drawings before construction.
• Keep the joint continuous through the required wall materials and finishes.
• Install bond breakers, backer materials, and sealants in the specified sequence.
• Do not cut reinforcement or change load paths without written design direction.
• Protect the joint from mortar droppings and debris that could lock it up.

Why concrete masonry walls move

Concrete masonry can shrink as units and mortar lose moisture after construction. Temperature changes also cause expansion and contraction, and the wall may move differently from adjacent steel, concrete or framed construction. A control joint creates a planned separation where movement can occur with a flexible sealant, helping reduce random cracking. It is not a crack repair; it is a designed movement detail.

The expected movement depends on unit type, moisture history, wall length, openings, restraint and exposure. Joint spacing and placement therefore come from the design and applicable masonry code or specification, not a universal spacing rule.

Coordinate the joint with the load path

A control joint may interrupt horizontal reinforcement, bond beams, flashing or other elements that cross the wall. The designer must specify how the wall’s structural role is maintained at the joint. A non-load-bearing veneer and a reinforced structural masonry wall do not use identical details.

Review drawings for joint locations at reentrant corners, changes in height, openings and material transitions. Do not move a joint to avoid an architectural feature without checking the resulting panel lengths and structural effects. If reinforcement or a bond beam is shown to continue, follow the detail or obtain an approved revision.

Seal the joint as part of the enclosure

The gap must remain capable of movement while limiting water and air leakage as designed. Backer rod controls sealant depth and prevents three-sided adhesion where specified; the sealant must be compatible with masonry and sized for the expected movement. Flashing and water-resistive barriers should terminate or transition correctly at the joint.

A rigid mortar bridge, grout spill, continuous coating or embedded finish can lock the joint and cause cracking nearby. Before sealant installation, clean and prepare the faces, confirm joint width and backing, and observe temperature and substrate conditions in the product instructions.

Inspect after installation and in service

Check that the joint is continuous through the intended wall height, is located where detailed, and has not been bridged by ties, mortar or finishes. Verify sealant adhesion and tooling, then inspect periodically for debonding, splitting or water entry. Repair should restore the movement capability, not simply cover a crack with a surface bead.

The adopted masonry code and project specifications govern. In an exam response, distinguish control joints in concrete masonry from expansion joints in other masonry systems and state that location and reinforcement details are design-dependent.

Example: a joint conflicts with reinforcement

A control joint shown near a window intersects a bond beam and vertical reinforcement. The mason should not stop bars at the joint or continue them through it based on habit. Compare the structural and architectural details, identify which reinforcement is intended to cross, and submit the conflict for design resolution. The engineer may revise the location, provide a movement-compatible connection or specify a different reinforcement detail. The sealant and flashing must still accommodate the movement joint.

Before laying the affected course, verify the approved revision, joint width, end conditions, bond-beam termination and sealant backing. Photograph concealed reinforcement and keep the approved detail with inspection records. If the wall is already built, do not saw a joint through reinforcement without design approval; that changes both structural behavior and crack-control assumptions.

Pre-close-in quality review

Before the wall is covered or sealant is applied, verify the joint location against the latest plan, confirm that mortar and grout have not bridged it, and inspect reinforcement or ties at the joint against the approved detail. Check that the joint extends through the components intended to move and that the sealant substrate is clean and sound.

Record deviations and obtain design approval before continuing. A control joint that is misplaced or locked by a rigid finish can shift cracking elsewhere; simply adding more sealant does not restore the intended movement plane.

Key takeaway

Control joints make movement more predictable, but they only work when located and built as designed. Treat them as structural and envelope details that require coordination, not as last-minute crack repairs.