Concrete Movement Joints:
Types, Spacing & Elimination
What Are Movement Joints in Concrete?
Concrete movement joints are the planned breaks in a slab that let it shrink, expand, and shift without cracking where you do not want it to. Concrete is never truly still. It shrinks as it cures, grows in heat, and moves against whatever it is tied to. The industry has managed that reality for decades with four joint types, and with pour strips that sit open on the critical path for weeks. We build the alternative. PS=Ø is an ICC Approved, ACI 318 Type 1 and Type 2 compliant mechanical rebar splice, engineered over 45 years to maintain structural continuity while allowing for the natural concrete volume change, so a construction joint no longer has to mean an open leave-out and a schedule delay.
Types of Movement Joints in Concrete Slabs
There are four movement joint types in structural concrete, and each one solves a different piece of the same problem. Knowing which is which is the difference between a slab that cracks on your terms and one that cracks on its own.
Expansion Joints
A full-depth gap that lets adjacent slabs grow toward each other in heat without crushing at the interface. Filled with a compressible material so the slab can expand and recover. Expansion joints are one type of concrete movement joint, and the head term most engineers reach for first.
Contraction (Control) Joints
A tooled or saw-cut groove that creates a weakened plane so drying-shrinkage cracks form where you want them, not randomly across the finish. Standard practice spaces these at roughly 24 to 36 times the slab thickness for interior slabs on grade.
Construction Joints
The stop-and-start line between two placements poured on different days. This is where pour strips and delay strips live: a leave-out that ties the reinforcement together after the concrete on either side has done most of its shrinking.
Isolation Joints
A separator that keeps a slab from bonding to columns, walls, footings, or equipment bases, so the slab can move independently without dragging a fixed element with it. Common around penetrations and at the slab-to-foundation interface.
Movement Joint Spacing in Concrete
Spacing is set by joint type, slab thickness, reinforcement, and exposure, and the engineer of record owns the final layout. The rules of thumb below are a starting point, not a substitute for a stamped detail.
- Contraction (control) joints: roughly 24 to 36 times the slab thickness for interior slabs on grade. Cut early, before shrinkage cracking starts on its own.
- Construction joints: located at planned placement stops, wherever the day's pour ends. This is the joint PS=Ø was built to replace.
- Expansion and isolation joints: driven by structural geometry, column lines, and penetrations rather than a fixed multiple.
Every joint you add is a place the finish opens up, water can enter, and a forklift wheel can chatter. That is the trade the industry has accepted for a century. Our angle is different: instead of detailing more joints to manage movement, eliminate the pour strip at the construction joint and keep the reinforcement continuous. For the expansion-joint side of this in detail, see our page on expansion joints, one type of concrete movement joint.
The Difference Between Movement Joints and Expansion Joints
The terms get used interchangeably on jobsites, but they are not the same. Movement joint is the category. Expansion joint is one member of it. Here is how the umbrella term breaks down.
| Joint Type | Movement It Handles | Where It Lives |
|---|---|---|
| Expansion | Thermal growth in heat | Long spans, slab-to-structure interfaces |
| Contraction / Control | Drying shrinkage | Saw-cut or tooled grooves in the field |
| Construction | Stops between placements | Pour strips and delay joints |
| Isolation | Independent slab movement | Around columns, walls, and penetrations |
All four are movement joints. PS=Ø targets the construction joint, replacing the open pour strip with a continuous, self-supporting splice.
How PS=Ø Maintains Structural Continuity While Allowing Concrete Movement
PS=Ø replaces the pour strip at a construction joint with an ICC Approved, ACI 318 Type 1 and Type 2 compliant mechanical rebar splice that stays continuous across the seam. A traditional delay strip leaves the reinforcement open for weeks so the slabs on either side can shrink before the closure is cast. Our system was engineered to let that same volume change happen while the splice holds the structural connection, so the joint closes without sitting open on the critical path.
Self-Supporting
Engineered to carry load without backshoring, leaving a clean floor for other trades and MEP.
Continuous Reinforcement
The splice maintains structural continuity across the joint instead of leaving rebar exposed in an open leave-out.
Natural Volume Change
Allows the concrete to shrink and move as it would with a pour strip, without the schedule cost of one.
Configurable Sizing
Available in 6, 8, 9, and 11 in both Grade 60 and Grade 80, and integrates with any rebar size. Typical lead time is 8 weeks.
When PS=Ø Is Not the Right Call
We would rather tell you this up front. If your slab only needs contraction control joints to manage drying shrinkage, saw-cutting is the correct answer, not a mechanical splice. PS=Ø replaces pour strips and delay joints at construction joints. It is not a substitute for the tooled or saw-cut grooves that steer shrinkage cracking, and it is not the tool for a small slab-on-grade with no leave-out to eliminate.
Where it earns its place is on structures carrying pour strips, delay strips, or restraint-to-shortening details you want off the critical path. Not sure which bucket your project falls in? Call (800) 355-8414 and one of our engineers will tell you straight.
What Eliminating Movement Joints Means on the Jobsite
Removing the pour strip at a construction joint changes the day for everyone who touches the slab. Engineers keep structural intent without detailing extra leave-outs. Placement and finishing crews pour continuously and skip the return trip to close the delay strip. For a crew-level view of how that plays out, read what eliminating movement joints means for placement and finishing crews.
Want the full mechanics of the seam?
Want the full mechanics of the seam, the couplers, the closure strip, and the grouting? Our self-supporting system that allows movement without a joint page walks through exactly what is included and how it installs.
Movement Joint FAQs
Do post-tensioned slabs still need movement joints? +
Yes. Post-tensioned slabs shorten more than conventionally reinforced ones because the tendons actively compress the concrete, so restraint-to-shortening is a bigger design concern, not a smaller one. Traditional PT detailing uses pour strips or delay strips left open for weeks to release that shortening before the closure is placed. The PS=Ø mechanical rebar splice maintains structural continuity across that line while still allowing the natural volume change, which lets teams close the gap without waiting out the full shortening period on the critical path.
Can you build a concrete slab without movement joints? +
You cannot eliminate concrete movement, it will shrink and respond to temperature no matter what. What you can eliminate is the visible joint that traditionally accommodates it. PS=Ø is an ICC Approved, ACI 318 Type 1 and Type 2 compliant mechanical splice engineered to maintain structural continuity while the concrete goes through its natural volume change, replacing the pour strip or delay joint at a construction joint with a small grouted seam instead of an open leave-out.
What is the difference between a movement joint and an expansion joint? +
Movement joint is the umbrella term for any joint designed to accommodate concrete volume change: expansion, contraction (control), construction, and isolation joints all fall under it. An expansion joint is one specific subtype that handles thermal growth. So every expansion joint is a movement joint, but not every movement joint is an expansion joint.
How far apart should movement joints be spaced? +
Spacing depends on joint type, slab thickness, reinforcement, and exposure, and the project engineer of record sets the final layout. As a general rule of thumb, contraction joints in interior slabs on grade are placed at roughly 24 to 36 times the slab thickness. Expansion and isolation joint locations are driven by structural geometry rather than a fixed multiple. Talk to our engineers about detailing for your specific slab.
Detailing a Slab? Let's Talk Joints.
Tell us about your project and our engineers will walk you through joint detailing and where PS=Ø can take a pour strip off the critical path.