Noticing cracks in your driveway, sidewalk, or garage floor? Don’t panic just yet.
Maybe you’ve spotted a faint hairline crack in your garage floor, or a driveway crack that seems to grow bigger each season. Should you be worried?
Here’s the truth: concrete almost always cracks. As the old saying goes, there are only two guarantees with concrete: it will get hard, and it will crack.
The challenge for homeowners is knowing which cracks are harmless and which ones could mean costly trouble.
TL;DR
- Almost all concrete cracks over time, but not all cracks are serious.
- Small, surface-level cracks (like shrinkage or crazing) are often cosmetic.
- Deeper or wider cracks (settlement, heaving, or structural) may require professional attention.
- Caulking and maintaining cracks early helps prevent expensive repairs later.
In This Article
- Shrinkage Cracks
- Overloading Cracks
- Hairline Cracks
- Settling Slab Cracks
- Heaving Slab Cracks
- Foundation Settlement Cracks
- Structural Cracks
- Crazing Cracks
- Crusting Cracks
- Re-Entrant Corner Cracks
- Internal Reinforcement Corrosion Cracks
- What Should You Do About Concrete Cracks?
- Frequently Asked Questions
1. Shrinkage Cracks
Shrinkage cracks show up in freshly poured concrete as it dries and cures. As water evaporates, the slab naturally shrinks, creating small surface cracks.
- Are they serious? Usually not. They’re superficial and don’t affect strength.
- How to reduce them: Proper curing practices (like keeping concrete moist while it sets) and shrinkage-reducing additives in the mix.
Concrete Gap and Crack Repair
Protect your concrete from settling and worsening cracks with professional concrete crack repair services.
2. Overloading Cracks
Concrete is strong, but it’s not indestructible. Overloading cracks form when too much weight is applied.
- Direct overload on a slab: Rare in residential settings.
- Overload on soft ground: More common. After heavy rain or snowmelt, water can soften the soil under your slab. Add a heavy RV, dumpster, or equipment on top, and the slab can crack.
Pro Tip: Concrete mixes are rated in PSI (pounds per square inch). Residential slabs are typically 3,000–4,000 PSI, meaning they can withstand thousands of pounds, but only if the soil beneath is stable.
3. Hairline Cracks
Hairline cracks are very thin but often run deep into the slab. They usually form as the concrete settles during curing.
- Why they matter: Like any crack, they are susceptible to worsening due to freeze-thaw cycles. Water seeps in, freezes, and expands, slowly prying the crack wider each winter.
- Solution: Watch to see if they widen over time, as sometimes they do not. Sealing growing hairline cracks can help prevent them from expanding.
4. Settling Slab Cracks
If the soil beneath concrete isn’t compacted correctly before pouring, it will settle over time and take the slab down with it.
Utility digs are a common culprit. If a company doesn’t backfill properly, that soil will settle later and leave voids under your slab.
Cracks often look different depending on where they form:
- In low spots: Cracks are pinched tightly together.
- In high spots: Cracks are pulled wider apart.
This kind of crack signals that the slab has lost support, which is a problem that usually calls for professional concrete lifting.
5. Heaving Slab Cracks
When the ground pushes concrete upward, you get heaving cracks. Two main culprits:
- Freeze-thaw cycles: Frozen soil expands and can lift slabs several inches. When it thaws, slabs drop back down to their original position. This movement causes cracking.
Expansion and control joints help manage this movement during installation. - Tree roots: Roots grow under slabs and act like a natural jack, forcing concrete upward until it cracks. Planting trees too close to driveways, sidewalks, or patios is a common mistake.
6. Foundation Settlement Cracks
Foundation settlement cracks are among the most serious cracks you’ll encounter.
- Where they appear: Corners or along foundation walls, often in a stair-step pattern.
- Cause: Uneven settlement from soil issues or poor site prep during construction.
Unchecked settlement cracks can threaten the integrity of the entire structure, so it’s important to inspect your foundation regularly for cracks or movement.
Pro Tip: If you can slide a quarter into the crack, it’s time to call a professional.
7. Structural Cracks
Structural cracks go beyond surface-level, cosmetic issues.
- Look: Typically ⅛” wide or more, running through the full thickness of the slab.
- Causes: Overloading, poor design, bad construction, shifting soil, or water intrusion.
- Risks: These cracks grow wider, allow leaks, and can potentially destabilize buildings.
Structural cracks almost always warrant inspection by a structural engineer or foundation repair specialist.
Concrete Gap and Crack Repair
Protect your concrete from settling and worsening cracks with professional concrete crack repair services.
8. Crazing Cracks
Crazing cracks look like a spiderweb of fine cracks on the concrete surface.
- Cause: The surface dried too fast during curing, causing the top layer to shrink at a different rate than the bottom.
- Impact: Crazing cracks are purely cosmetic, but they can make concrete look prematurely aged.
Pro Tip: Sealing the slab with a penetrating sealer may prevent the crazing cracks from worsening over time.
9. Crusting Cracks
When concrete is curing, hot, sunny, or windy conditions can dry the surface of concrete faster than the layers beneath. The result is a brittle, crusty top layer that cracks as the slab cures.
- Common with: Stamped concrete, where added texture makes the surface even more prone to uneven drying.
- Impact: Only surface-level; not a structural threat.
These cracks aren't structural , but they can detract from the slab’s appearance.
10. Re-Entrant Corner Cracks
Anytime concrete is poured around a corner, notch, or object (like a manhole or column), it’s prone to re-entrant corner cracks that radiate out from the object.
- Cause: Uneven shrinkage during curing.
- Solution: Contractors often install control joints when the concrete is poured to “direct” these cracks into predictable, less visible areas.
11. Internal Reinforcement Corrosion Cracks
Reinforcing steel (like rebar or mesh) strengthens concrete, but it has a weakness: rust.
- Cause: Moisture penetrates the slab, corroding steel. Rust expands, pushing outward until the surrounding concrete cracks and spalls.
- Impact: Serious long-term deterioration if not addressed.
This type of crack is often seen in aging or poorly sealed slabs where water has been allowed to penetrate for years.
What Should You Do About Concrete Cracks?
- Inspect regularly. Check driveways, patios, sidewalks, garage floors, and foundations for new cracks.
- Caulk early. Flexible concrete caulk prevents worsening damage due to water intrusion.
- Seal the surface. Applying a high-quality penetrating sealer to the surface helps prevent freeze-thaw damage.
- Know when to call a pro. Settlement, heaving, and structural cracks often require more than a DIY fix.
At A-1 Concrete Leveling, we’ve been restoring cracked and settled slabs nationwide for over 30 years. Request a free estimate from your local A-1 Concrete Leveling team today.
Still Deciding?
- How to Fill, Seal & Caulk Concrete Cracks
- Why Your New Concrete Is Cracking (and When to Worry)
- What Causes Concrete Spalling (and What Actually Fixes It)
Frequently Asked Questions
Are all concrete cracks bad?
No, not all concrete cracks are bad. Many cracks are cosmetic and don’t threaten structural integrity.
Should I seal small cracks?
Yes, it's good practice to seal small cracks. Even hairline cracks can let water in, which worsens damage during freeze-thaw cycles.
When do I need professional help?
If a crack is constantly widening, shows signs of movement, or appears in your foundation, it’s time to call a pro.
Can cracks be completely repaired?
Surface-level cracks can be caulked or patched, but once a slab cracks, only full replacement removes it completely. The goal is usually the prevention of further damage, not making cracks invisible.
Concrete Gap and Crack Repair
Protect your concrete from settling and worsening cracks with professional concrete crack repair services.
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