The Truth About Concrete Cracks: When to Patch and When to Cut

There is an old saying in our industry: "There are two types of concrete: concrete that has cracked, and concrete that is going to crack."

Cracks are inevitable. But they confuse homeowners. Is that thin line in your driveway a structural disaster? Or just a cosmetic wrinkle? Should you fill it with a tube of caulk from the hardware store? Or do you need to cut the concrete?

Understanding the type of crack you have is critical to choosing the right repair. Treat a structural crack like a cosmetic one, and it will just break open again next week. Treat a cosmetic crack like a structural one, and you've wasted money. Here is the truth about concrete cracks.

Type 1: The Hairline / Shrinkage Crack

What it looks like: Thin, spiderweb-like cracks that don't go all the way through the slab. You can't fit a credit card into them.

Cause: When concrete cures, it shrinks. If it cures too fast (hot day, not enough water), the surface pulls apart slightly.

The Fix: Patch/Resurface. These are cosmetic. Water can get in and freeze, making them bigger, so they should be sealed. But you don't need to cut them. We use a flowable polymer healer/sealer or a resurfacing overlay to cover them up.

Type 2: The Settlement Crack

What it looks like: A wider crack where one side of the concrete is lower than the other. It creates a "step" or trip hazard.

Cause: The dirt underneath has washed away or settled. The slab is breaking its back trying to bridge the gap.

The Fix: Lift, Then Patch. You cannot just fill this. If you fill it, the ground is still hollow, and it will just sink more and crack the fill. We must first Lift the slab back to level (using foam) to stabilize the subgrade. Once it is supported, then we patch the crack.

Type 3: The Expansion / Heave Crack

What it looks like: A crack that opens and closes with the seasons, or concrete that is crushing itself against a wall or another slab.

Cause: Thermal expansion. Concrete expands in summer. If there are no "expansion joints" (gaps with soft material), the concrete has nowhere to go but up (heave) or crack.

The Fix: Cut. You cannot patch this tight. If you fill an expansion crack with hard mortar, when the concrete expands again next summer, it will crush your patch. We must fix this by recutting the expansion joint to give the slab room to move, then sealing it with a flexible sealant (like polyurethane) that moves with the slab.

Type 4: The Structural / Root Crack

What it looks like: A wide, jagged crack pushing up, often with multiple branches. The concrete feels loose or rocks when you drive on it.

Cause: Tree roots pushing up, or a total failure of the sub-base.

The Fix: Cut and Replace. This is where Sectional Replacement is mandatory. No patch in the world will hold back a 50-year-old oak tree root. We must cut out the damaged section, remove the root, and pour new concrete.

Conclusion

Don't just squeeze a tube of "Crack Fix" into a hole and hope for the best. Diagnose the crack. Is it moving? Is it sinking? Is it shrinking?

At Charlotte Concrete Repair, we diagnose the physics of the failure before we prescribe the cure. That is the difference between a repair that lasts 6 months and one that lasts 20 years.