If you look closely at a concrete driveway, patio, walkway, or garage floor, you will probably notice straight lines running across the surface. Some may have been saw-cut into the concrete, while others may contain flexible material separating one slab from another.

These lines are not imperfections.

They are joints, and they play an important role in helping concrete accommodate the movement that naturally occurs after installation.

Concrete is extremely strong, but it is not completely motionless. It shrinks as it cures and responds to changes in temperature and moisture. According to the Federal Highway Administration’s guidance on concrete pavement joints, properly designed joints help control cracking and accommodate situations where different concrete sections or structures may move differently.

This becomes particularly important in Ottawa, where concrete surfaces experience significant seasonal temperature changes, freezing conditions, summer heat, moisture, snow, and repeated freeze-thaw cycles.

Understanding what concrete joints do can help homeowners recognize why those carefully placed lines are an important part of professional concrete construction rather than something that should be avoided.

Why Does Concrete Move?

Concrete may appear completely rigid after it hardens, but small dimensional changes continue throughout its life.

Movement can result from:

• Drying shrinkage
• Temperature changes
• Moisture changes
• Ground movement
• Structural loading

The Federal Highway Administration explains that concrete’s coefficient of thermal expansion describes how its dimensions respond to changes in temperature. Temperature changes influence joint opening and closing and can contribute to stresses within concrete slabs.

In simple terms, concrete becomes slightly larger or smaller as conditions change.

The movement may be small, but across a large slab it can create substantial stress.

Why Does Concrete Crack?

Some amount of cracking is a natural possibility with concrete.

As newly placed concrete loses moisture, it shrinks. At the same time, the slab can be restrained by the base beneath it and surrounding structures.

Temperature changes introduce additional movement.

If the tensile stress becomes greater than the concrete can accommodate, a crack may form.

Joints provide predetermined locations where this movement can occur in a controlled way.

Rather than expecting concrete never to crack, professional installation focuses partly on controlling where expected shrinkage cracking develops.

What Is a Control Joint?

A control joint is also commonly called a contraction joint.

These are the straight grooves homeowners frequently see across concrete surfaces.

According to FHWA guidance on concrete contraction joints, control joints create weakened planes intended to influence where cracks caused by shrinkage and temperature-related stresses develop.

Instead of allowing a visible random crack to travel unpredictably across a driveway or patio, the joint encourages cracking to occur beneath the planned groove.

This can produce a much cleaner and more controlled finished surface.

Control Joints Don’t Mean the Concrete Is Broken

This is an important distinction.

When a contraction joint performs correctly, a crack may actually develop below the visible joint.

That’s part of its purpose.

The visible groove provides a planned location where the slab can separate slightly as shrinkage and temperature changes occur.

Without appropriate control joints, the concrete may choose its own cracking locations.

Those random cracks can cross:

• Driveways
• Patios
• Walkways
• Garage floors
• Decorative areas

Proper joint planning therefore contributes to both performance and appearance.

What Is an Expansion Joint?

Expansion joints serve a different purpose.

While control joints help manage shrinkage-related cracking, expansion or isolation joints allow concrete to move independently from adjoining structures or other concrete elements.

The FHWA’s concrete pavement guidance describes expansion joints as joints placed at specific locations to allow concrete expansion without damaging adjoining pavement or structures.

Around residential properties, isolation-type joints may be particularly important where concrete meets:

• Foundation walls
• Columns
• Existing slabs
• Stairs
• Other fixed structures

The goal is to prevent movement in one concrete element from placing unnecessary pressure on another.

Control Joints and Expansion Joints Are Not the Same

Although homeowners sometimes use the terms interchangeably, their purposes are different.

Control Joints

Control joints are designed primarily to control where shrinkage and temperature-related cracking occurs.

Expansion or Isolation Joints

These allow movement between concrete and adjoining structures or separate concrete elements.

A professionally planned project may use different joint types depending on the layout and conditions.

Understanding that distinction is important because simply adding more lines to concrete doesn’t automatically improve its performance. The joints need to be appropriate for the application.

Why Ottawa’s Temperature Changes Matter

Ottawa experiences significant temperature variation throughout the year.

A concrete driveway can experience summer heat followed only months later by deeply freezing winter conditions.

Temperature changes cause concrete to expand and contract.

FHWA research into temperature-related concrete joint movement notes that temperature changes strongly influence how joints open and close.

This is one reason joint design matters so much in climates with large seasonal temperature differences.

Properly planned joints give the slab a way to accommodate expected movement.

Freeze-Thaw Conditions Add Another Challenge

Ottawa concrete must also cope with moisture and freezing temperatures.

Water can enter concrete or the surrounding soil. When temperatures fall, freezing conditions can contribute to stresses and movement within the overall concrete system.

Joint placement does not eliminate freeze-thaw exposure, but good concrete design combines several important elements:

• Appropriate concrete mix
• Proper base preparation
• Effective drainage
• Correct curing
• Suitable joint placement
• Ongoing maintenance

Together, these factors help concrete withstand Ottawa’s climate more effectively.

Control Joints Are Especially Important in Driveways

Residential driveways often contain large areas of concrete.

Without appropriate joint planning, large uninterrupted slabs have greater opportunity to develop random cracks.

Control joints divide the driveway into more manageable sections.

A properly designed driveway considers:

• Slab dimensions
• Thickness
• Layout
• Drainage
• Vehicle loads
• Joint locations

The goal is to balance appearance with long-term performance.

Walkways Need Proper Joint Planning Too

Because concrete walkways are long and relatively narrow, joints are an important part of their design.

Without properly placed joints, shrinkage may create cracks across unexpected locations.

Joint placement can also be coordinated with the overall design so that the lines appear intentional rather than disruptive.

For example, joints can sometimes complement:

• Pathway dimensions
• Landscaping
• Entrance layouts
• Decorative patterns

Good concrete work considers both engineering requirements and appearance.

Concrete Stairs Have Their Own Movement Considerations

Concrete stairs often interact with landings, walkways, porches, and other structures.

Where two concrete elements may move differently, proper separation becomes important.

Without appropriate planning, movement can contribute to:

• Cracking
• Edge deterioration
• Separation
• Pressure between adjoining structures

Because stairs are also a safety-critical feature, professional planning and construction are particularly important.

Patios Can Develop Random Cracks Without Proper Joints

Backyard patios can contain substantial uninterrupted areas of concrete.

As the slab cures and experiences temperature changes, stresses develop.

Properly located control joints help manage where cracking occurs.

This becomes particularly important with large outdoor entertainment spaces containing:

• Dining areas
• Outdoor kitchens
• Fire pits
• Seating areas
• Pergolas

Joint planning should therefore be considered during the initial patio design rather than after concrete has already been placed.

Decorative Concrete Requires Careful Joint Planning

Homeowners sometimes worry that control joints will interfere with the appearance of decorative concrete.

Professional planning can often incorporate the joints into the design.

They may align with:

• Borders
• Pattern transitions
• Geometric layouts
• Architectural features

This allows necessary joints to become part of the finished design rather than looking like an afterthought.

Ignoring joint requirements purely for aesthetic reasons can increase the likelihood of random cracking that is far more noticeable.

Stamped Concrete Still Needs Joints

Stamped concrete may resemble stone, slate, brick, or other materials, but underneath the decorative pattern it remains concrete.

That means it still experiences shrinkage and temperature-related movement.

Joint locations should therefore be considered when designing stamped surfaces.

Experienced installers may integrate control joints with the pattern so they appear as natural divisions within the finished surface.

Good joint planning helps protect both structural performance and decorative appearance.

Garage Floors Also Need Control Joints

Large garage concrete slabs experience curing shrinkage and temperature changes just like exterior concrete.

Control joints help divide the slab into appropriate sections and manage cracking.

Garage floors also support:

• Vehicles
• Storage systems
• Workbenches
• Equipment

Proper joint design is therefore part of creating a durable garage floor.

If the floor will eventually receive residential epoxy flooring, existing joints and cracks should be properly evaluated during surface preparation rather than simply covered without consideration.

Why Joint Spacing Matters

Control joints cannot simply be placed randomly.

Spacing depends on factors such as:

• Slab thickness
• Concrete properties
• Dimensions
• Reinforcement
• Base conditions
• Environmental conditions

FHWA research on concrete joint spacing and cracking emphasizes that spacing must balance the need to control cracking with the structural characteristics of the pavement system.

Residential concrete is not identical to highway pavement, so homeowners should not simply copy roadway specifications. The underlying principle remains useful: joint spacing needs to be designed for the actual slab rather than chosen arbitrarily.

Joint Depth Matters Too

A control joint needs sufficient depth to create an effective weakened plane.

If a saw cut is too shallow, the concrete may crack somewhere else instead.

FHWA guidance for certain concrete pavement applications recommends contraction-joint saw cuts around one-third of the slab depth to create an adequate weakened plane.

The exact requirements for a residential project depend on the design, installation method, and conditions.

This is one reason control joints should be handled by experienced concrete professionals.

Timing Is Critical When Cutting Control Joints

Saw-cut joints need to be created at the appropriate stage of concrete curing.

Cut too early, and the concrete may not have enough strength to produce a clean cut.

Wait too long, and uncontrolled cracking may already have begun.

Professional installers monitor concrete conditions and choose an appropriate cutting window.

Temperature, weather, concrete mixture, and curing conditions can all influence timing.

What Happens When Control Joints Are Missing?

Large concrete slabs without adequate control joints may develop random cracking.

Homeowners might notice cracks:

• Across the centre of a driveway
• Diagonally from corners
• Through patio areas
• Across walkways
• Through garage floors

Random cracking does not automatically mean the entire slab has failed.

However, cracks should be monitored and evaluated, particularly when they widen or show vertical movement.

Professional concrete repair may help address appropriate cracks before moisture and seasonal conditions contribute to further deterioration.

What Happens When Joints Become Filled With Debris?

Joints need room to perform their intended function.

Over time, they can collect:

• Sand
• Dirt
• Small stones
• Organic material

If incompressible material fills a joint, it can interfere with movement as the concrete expands.

The FHWA notes that incompressible material trapped in joints can generate high compressive stresses when slabs expand, potentially contributing to joint spalling.

Keeping joints reasonably clean is therefore an important maintenance practice.

Should Cracked Joints Be Repaired?

Some deterioration around joints is cosmetic, while other damage may require attention.

Watch for:

• Widening cracks
• Chipped joint edges
• Spalling
• Vertical movement
• Water infiltration
• Sections separating noticeably

The appropriate solution depends on what caused the damage.

Simply filling every visible opening without understanding how the joint is intended to move may not provide the best long-term result.

Can Old Concrete With Joint Problems Be Resurfaced?

Potentially.

If an older slab remains structurally suitable but has surface deterioration, concrete resurfacing may restore its appearance.

However, existing joints should not simply be ignored.

The condition and location of joints, cracks, settlement, and underlying movement should all be considered before resurfacing begins.

A new surface cannot correct an unstable base or eliminate necessary movement within the original concrete.

Joints Near Foundations Deserve Special Attention

Concrete adjoining a home should not place unnecessary stress against the foundation as movement occurs.

Proper isolation between different structural elements can help allow independent movement.

Homeowners should also watch for water collecting along joints close to the house.

If significant cracking, settlement, or moisture problems are affecting the structure itself, professional foundation repair may need to be considered separately from cosmetic concrete work.

Why Professional Installation Makes Such a Difference

Joints may look simple, but proper design requires careful planning.

Experienced concrete professionals consider:

• Slab dimensions
• Concrete thickness
• Property layout
• Temperature exposure
• Drainage
• Reinforcement
• Fixed structures
• Intended use
• Decorative design

They also determine when and how joints should be created.

These decisions can have a major influence on how the finished concrete performs over time.

Can Joints Completely Prevent Cracking?

No responsible concrete contractor should promise completely crack-free concrete.

Concrete naturally changes dimensions as it cures and responds to its environment.

Control joints are designed to manage cracking, not magically eliminate every possibility of it.

The objective is to encourage expected cracking to occur at planned locations where it is less visible and easier for the slab to accommodate.

Good installation combines joint planning with proper base preparation, concrete placement, curing, drainage, and maintenance.

Inspect Your Joints Every Spring

Ottawa homeowners should include concrete joints in their annual spring inspection.

After winter, check for:

• Debris buildup
• Damaged joint edges
• Spalling
• New cracks
• Widening gaps
• Uneven sections
• Standing water

Early identification of deterioration can make maintenance easier and help protect surrounding concrete.

Conclusion

Expansion and control joints may appear to be simple lines in concrete, but they perform an important role in helping concrete manage natural movement.

Control joints provide planned locations for shrinkage and temperature-related cracking, while expansion or isolation joints help separate concrete elements that need to move independently. Both can contribute to the long-term performance of driveways, patios, walkways, stairs, garage floors, and other residential concrete surfaces.

For Ottawa homeowners, joint design becomes especially important because concrete must perform through significant seasonal temperature changes and challenging winter conditions.

Proper joint placement, depth, timing, drainage, and maintenance all contribute to a concrete surface that performs as intended.

Rather than viewing joints as interruptions in the finished concrete, homeowners should see them for what they really are: carefully planned features designed to help protect a long-term investment.

Frequently Asked Questions

What is a control joint in concrete?

A control joint, also called a contraction joint, creates a planned weakened location intended to control where shrinkage and temperature-related cracking occurs.

What is an expansion joint?

An expansion or isolation joint provides separation that allows concrete to move without placing excessive pressure on adjoining concrete or fixed structures.

Are expansion joints and control joints the same?

No. Control joints primarily manage the location of cracking, while expansion or isolation joints accommodate movement between separate concrete elements or structures.

Why does concrete need control joints?

Concrete shrinks as it cures and changes dimensions as temperature and moisture conditions change. Control joints help manage the stresses created by this movement.

Do control joints stop concrete from cracking completely?

No. Their purpose is generally to influence where expected cracking occurs rather than guarantee that no cracks will ever form.

Does stamped concrete need control joints?

Yes. Stamped concrete is still concrete and experiences the same shrinkage and temperature-related movement. Joints can often be incorporated into the decorative pattern.

Can control joints be added after concrete is poured?

Saw-cut control joints are normally created after placement at an appropriate stage of curing. Timing is important because waiting too long may allow random cracking to occur first.

Why are there joints in my garage floor?

Garage slabs experience curing shrinkage and temperature changes. Control joints help manage cracking by dividing the slab into planned sections.

Should concrete joints be kept clean?

Yes. Dirt, stones, and other incompressible materials can interfere with joint movement and may contribute to deterioration around joint edges.

When should damaged concrete joints be professionally inspected?

Professional evaluation is recommended when you notice significant spalling, widening cracks, vertical movement, settlement, recurring water infiltration, or deterioration spreading away from the joint.