Walk into almost any garage and you’ll notice straight lines cut into the concrete. Many homeowners assume these are simply cracks or cosmetic features, but they’re actually one of the most important parts of a properly constructed concrete slab.
Understanding the difference between concrete control joints vs expansion joints helps homeowners better understand why concrete behaves the way it does and why professional garage floor coating contractors pay close attention to every joint before beginning an installation.
At Precision Concrete Coating, every garage floor is carefully inspected before surface preparation begins because joints play an important role in both concrete performance and coating longevity.
Why Does Concrete Need Joints?
Concrete is incredibly strong under compression, but it naturally expands, contracts, shrinks, and moves throughout its lifetime.
Temperature changes, moisture, curing, and seasonal movement all cause the slab to change slightly over time.
Without joints, concrete would crack randomly across the surface.
Instead, properly designed joints help control where that movement occurs.
What Are Control Joints?
Control joints are intentionally placed grooves that encourage concrete to crack in a straight, predictable location rather than randomly.
Knowledge Node: Control Joint
A control joint is a planned weakened section of concrete designed to control where shrinkage cracks occur as the concrete cures.
Concrete naturally shrinks as it loses moisture after placement. Rather than preventing cracking altogether, control joints simply direct where those cracks are most likely to develop.
What Are Expansion Joints?
Expansion joints serve a completely different purpose.
Knowledge Node: Expansion Joint
An expansion joint is a full-depth separation between two concrete sections that allows them to expand and contract independently without placing pressure on one another.
Expansion joints are commonly found:
- Around garage walls
- At driveway connections
- Near foundations
- Between slabs
- Around structural columns
Unlike control joints, expansion joints are designed to remain open and flexible.
Why This Matters Before Installing a Garage Floor Coating
One of the most common homeowner questions is whether every joint should simply be filled before applying a coating.
The answer is no.
Professional installers evaluate every joint individually.
Control joints may be treated differently than expansion joints depending on the coating system and the expected movement of the slab.
As explained in Garage Floor Coating Preparation Why Surface Preparation Matters More Than The Coating, proper joint evaluation is one of the most important parts of a professional installation.
Surface Preparation Begins With Joint Inspection
Before any coating is installed, contractors inspect:
- Existing cracks
- Control joints
- Expansion joints
- Surface deterioration
- Moisture conditions
- Previous repairs
This inspection occurs before Surface Preparation for Garage Floor CoatingsWhy Surface Preparation Matters More Than The Coating begins.
Once the slab has been evaluated, contractors perform mechanical grindingGarage Floor Grinding Process to expose sound concrete and create the proper surface for coating adhesion.
Our guide Why Mechanical Grinding Matters for Garage Floor Coatings Mechanical Grinding For Garage Floor Coatings explains why preparation—not simply applying the coating—is what determines long-term performance.
Concrete Continues to Move
Many homeowners believe concrete stops changing after it hardens.
In reality, concrete continues moving throughout its lifetime.
Knowledge Node: Thermal Expansion
Concrete expands when temperatures rise and contracts when temperatures fall. This movement may be small, but across an entire slab it creates enough stress that properly designed joints are essential.
This movement is one reason expansion joints should never be ignored during a professional coating installation.
Moisture Also Affects Movement
Concrete isn’t waterproof.
Moisture enters and leaves the slab throughout its life, causing small dimensional changes.
Professional contractors often evaluate moisture before coating installation because excessive moisture can affect both the concrete and the coating system.
Learn more in Why Moisture Testing Matters Before Garage Floor Coating Installation.Concrete Moisture Testing Explained
What About Existing Cracks?
Not every crack indicates structural failure.
Many cracks are simply shrinkage cracks that formed exactly where the control joint was designed to guide movement.
Others may require professional repair before coating.
Our articles Why Concrete Cracks Before You Ever Install a Garage Floor Coating, How Concrete Shrinkage Affects Garage Floor Coatings, Understanding Concrete Delamination, Why Concrete Scaling Happens, and Understanding Concrete Spalling explain the different types of concrete damage professionals evaluate during installation.
Why Joint Evaluation Protects Your Investment
Garage floor coatings perform best when the slab is properly prepared and natural concrete movement is respected.
Simply filling every joint without understanding its purpose can create unnecessary stress within the coating system.
Professional installers understand which joints should remain flexible, which repairs are appropriate, and how to prepare the slab for long-term performance.
This knowledge is one reason professionally installed systems consistently outperform many DIY coating kits.
Frequently Asked Questions
Do control joints stop concrete from cracking?
No. They encourage cracks to occur in a planned location instead of randomly across the slab.
Should expansion joints be filled before coating?
Not always. Expansion joints are designed to allow movement and are evaluated individually during professional installation.
Why are joints important?
They reduce stress within the slab and help prevent uncontrolled cracking.
Can garage floor coatings cover joints?
Professional contractors determine the best approach for each joint based on its purpose and expected movement.
Does every garage have control joints?
Most residential garage floors include some combination of control joints, expansion joints, or both.
Final Thoughts
Control joints and expansion joints may look similar, but they serve very different purposes. Understanding how concrete moves helps explain why professional contractors spend so much time evaluating the slab before installing a coating. Proper joint inspection, mechanical grinding, moisture evaluation, crack repair, and surface preparation all work together to create a garage floor coating built for long-term performance.
To continue learning about professional concrete preparation, explore Surface Preparation for Garage Floor Coatings, Garage Floor Coating Preparation, Why Mechanical Grinding Matters for Garage Floor Coatings, Understanding Concrete Surface Profile (CSP), Why Concrete Cracks Before You Ever Install a Garage Floor Coating, How Concrete Shrinkage Affects Garage Floor Coatings, Understanding Concrete Delamination, Why Concrete Scaling Happens, Understanding Concrete Spalling, Why Moisture Testing Matters Before Garage Floor Coating Installation, Premium Garage Floor Coatings, and Polyaspartic vs Epoxy Garage Floor Coatings. Together, these resources explain why understanding concrete itself is the foundation of every successful garage floor coating.
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