For most concrete masonry unit (CMU) walls, the movement joint people need to understand is a control joint, which accommodates shrinkage in concrete masonry. An expansion joint is primarily used to accommodate expansion in clay masonry and is typically not used as the standard movement joint in CMU construction. Check the exact joint name and detail on the project drawings.
There is no universal “CMU expansion-joint spacing” that can be applied to every block wall. If a plan is asking for CMU crack control, use the project’s control-joint layout and reinforcement details. The CMU control-joint guide covers spacing criteria and placement considerations for those joints.
| Joint type | Movement it addresses | How to think about it in CMU work |
|---|---|---|
| Control joint | Primarily longitudinal shrinkage movement and related stress in concrete masonry | A common CMU crack-control detail; locate, reinforce, and seal it as shown in the approved design |
| Expansion joint | Expansion of an adjoining masonry material or building section | Commonly associated with clay brick expansion; not the default joint for ordinary CMU shrinkage control |
| Isolation or movement joint | Relative movement between a wall and an adjoining material or building component | Use the specific term and detail on the plans; the connection may need to remain separate or transfer selected loads |
CMU expansion joints vs. control joints
The words are often used loosely, but the joint type matters. Concrete masonry units can shrink as they dry. A control joint creates a planned vertical plane that allows limited movement and helps manage where shrinkage-related cracking occurs. It is not a promise that a wall will never crack.
Clay masonry behaves differently: it tends to expand with moisture and temperature exposure. Expansion joints are commonly detailed to accommodate that brick movement. CMU walls can also move at connections or interfaces, but that does not make a brick expansion-joint spacing rule appropriate for a block wall.
Industry guidance from the Concrete Masonry & Hardscapes Association describes expansion joints as primarily used with clay masonry and typically not used with concrete masonry construction. The construction documents should identify the intended joint and its purpose.
What is the recommended spacing for a CMU expansion joint?
There is no single recommended expansion-joint interval for all CMU walls. For a CMU wall needing shrinkage crack control, the designer generally evaluates control joints, not a generic brick expansion-joint spacing chart. Control-joint spacing can depend on wall geometry, unit height, reinforcement, openings, movement conditions, and the applicable design method.
Use the control-joint schedule and drawings for the project. They should show the joint locations and any conditions for the wall type. For common CMU control-joint spacing concepts, limits, and examples, use the linked control-joint spacing guide; its values apply only to the stated conditions and are not an expansion-joint rule.
Where CMU movement joints may be considered
The designer may review locations where wall geometry, support, or adjoining construction changes the way movement is restrained. Examples include changes in wall height or thickness, openings, corners, wall intersections, and movement joints in floors or roofs. These are review points, not automatic locations or a substitute for the structural layout.
Building movement, settlement, seismic separation, and a change between different materials may call for a different detail than a shrinkage control joint. For the broader causes and signs of masonry movement, see the CMU wall movement guide.
What to check on the joint detail
Before work starts, match the joint tag on the elevation to the detail and specification. Confirm:
- the joint type, location, width, depth, and how far it continues through the wall;
- the specified block ends, bond-break material, backer rod, sealant, gasket, or waterstop;
- which bed-joint reinforcement, bars, or bond-beam reinforcement stop, pass through, or receive a special connection;
- how the joint relates to openings, lintels, roof/floor connections, waterproofing, fire resistance, and weather exposure; and
- the sealant product, movement capacity, substrate preparation, and inspection requirements in the project documents.
Control joints often interrupt ordinary horizontal reinforcement so the joint can accommodate movement. Structural reinforcement may need to remain continuous for load transfer. Never cut, extend, or stop a bar based on a generic online diagram; follow the specific engineered detail and request clarification if it is missing or conflicts with the wall schedule. The CMU rebar spacing guide explains how to read reinforcement notes on wall plans.
Sealant and water-management details
A movement joint exposed to weather may need a flexible, compatible sealant and backing material to maintain the building-envelope seal as the joint moves. The approved detail determines the joint geometry, materials, primer, drainage or flashing relationship, and fire or sound requirements. A rigid mortar fill is not a substitute where the design calls for a movement-capable seal.
If an existing CMU wall has cracks or water entry, first identify whether the issue is a movement joint, a shrinkage crack, or another defect. The CMU wall crack repair guide explains how to assess cracks before selecting a repair.
Common CMU joint mistakes
- Calling every movement detail an “expansion joint” and overlooking that CMU shrinkage is usually addressed with control-joint design.
- Copying a clay-brick expansion-joint spacing into a concrete block wall.
- Using a one-size-fits-all interval without checking the wall height, openings, reinforcement, and plan details.
- Assuming all reinforcement should stop at a joint, or that all reinforcement can cross it continuously.
- Filling a specified movement joint with rigid mortar or a sealant that cannot accommodate the required movement.
- Ignoring waterproofing, fire-rating, lintel, diaphragm, or structural continuity requirements at the joint.
Frequently asked questions
Are expansion joints used in CMU walls?
CMU walls usually use control-joint design for shrinkage-related movement. Expansion joints are primarily associated with accommodating clay masonry expansion and are typically not used as the standard joint in concrete masonry. A project may still require an isolation or other movement detail at a specific interface.
Are CMU control joints and expansion joints the same?
No. A control joint is commonly used to manage shrinkage movement in concrete masonry. An expansion joint accommodates expansion in materials or building sections that need that type of separation. The plan detail controls the joint type.
Can I use a standard expansion-joint spacing for a CMU wall?
No universal spacing applies. First confirm whether the drawing calls for a CMU control joint, an isolation joint, or a different movement detail. The designer sets spacing and placement for the wall’s conditions.
Should rebar or joint reinforcement continue through a CMU control joint?
Do not assume either way. Ordinary horizontal reinforcement may be interrupted at a control joint, while selected structural reinforcement may need continuity or a designed transfer detail. Follow the drawings and ask the project engineer about unclear conditions.
What sealant should be used at a CMU movement joint?
Use the sealant and backing materials listed in the approved detail. They must suit the joint movement, masonry substrates, exposure, and any fire or weather requirements for that wall.
Key takeaway
For CMU walls, distinguish a shrinkage control joint from a clay-masonry expansion joint and from an isolation joint between adjoining components. Do not apply generic expansion-joint spacing to a concrete block wall. Follow the approved joint schedule, reinforcement, sealant, and structural details; use the control-joint guide for CMU spacing information.