How Deep Should Expansion Joints Be Cut in Concrete?

Expansion joints are important to the quality and life of any concrete area.

Joint Depth Determined by Concrete Depth

Expansion joints, like other control joints, are designed to ensure that when your concrete cracks, as it will eventually, it cracks where you want it to. The joints should be cut to approximately 25 percent of the depth of the concrete. For example, a 4-inch deep slab should have expansion joints that are at least 1 inch deep. Not cutting deeply enough may mean cracks will travel or otherwise not follow the path of your expansion joint.

Cut Deep Enough

Regardless of the depth of your concrete slab, your joint should be cut at least 1-inch deep. In cases of shallow concrete slabs, this may mean you are 50 percent or more of the way through. This is fine in most concrete applications and will allow your concrete to expand and contract without damage.

Bottom Line

Cutting to a depth of 1-inch or 25 percent of the depth of your concrete, whichever is higher, will give your concrete the room it needs. This will protect your work and investment for years to come.

References

• Placing Control Joints in Concrete
• John Bridge.com: Control Joints
• NRMCA: Concrete in Practice