Let’s crack the surface on this question
There’s nothing like the smooth, flawless look of freshly-poured concrete. So of course it’s frustrating to spot any hairline cracks—especially if you just paid for a new driveway, concrete slab, walkway, or garage floor. But you typically don't need to worry if you see fine lines, spider-web lines, or shattered-glass lines on your concrete’s surface. Here’s why you have cracks in your new concrete, and what you can do about it.
Why Are There Cracks in Fresh Concrete?
It’s natural to worry about cracks in freshly poured concrete. The truth is, some cracks are inevitable due to the structure of the surface. Let’s dive in to the reason your fresh concrete may crack.
Common Reasons for Concrete Cracks
Both hairline cracks and shrinkage cracks occur because of moisture loss.
Common reasons for cracking include:
"Plastic shrinkage" from water loss
Temperature, humidity, and wind
Too much water added to mix
Concrete dried too quickly
In older driveways, soil pressure is a big cause of cracks in concrete foundation blocks. Some other causes of long-term driveway cracks include everything from nearby trees to heavy vehicles.
Will Hairline Cracks in Fresh Pavement Go Away?
Yes, in about a month, hairline cracks should subside. While shrinkage cracks can show up on the surface within hours of having concrete poured, it takes a full month for new concrete to fully settle.
Don't be surprised if cracks that seemed visible at first are nearly impossible to see after a month of settling. You should be able to decide if you can live with the cracks by then. Any crack that's one-eighth of an inch or smaller is considered standard.
Signs That Fresh Concrete Was Poured Improperly
If you see cracking or curling, it's possible that your concrete dried faster than it should have during pouring. It's usually the case when you see small surface cracks.
If you notice uneven cracks that are larger than 1 inch, it's often a sign of a bigger problem requiring you to replace or repair your sidewalk or driveway. A good test is if you can fit a quarter in the crack.
Any crack that is 1/8 of an inch or less is typically considered a harmless hairline crack. Tell your contractor if you think something went wrong during pouring.
In fact, you can consider the following options if you have suspicions about the work:
Bring the contractor back to go over your concerns
Have a supplier representative take a look
Have another contractor inspect the job to give a third-party perspective
Some Concrete Cracks Are Planned
When cracks can’t be prevented, concrete contractors often use control joints to, well, control where the cracks will end up. Think of cracks in the sidewalk.
Here's how it works:
The contractor spaces the control joints in the concrete
The joints relieve pressure
Cracks form in the right spots
Cracking is undetectable
When to Worry About Cracks in Concrete
Keep an eye on cracks to make sure they’re not a sign of a larger problem. Here are some potential problems if a crack gets wide enough for water to seep into the slab:
Water can rust your rebar
Rusting/cracking weakens the foundation
Frozen water in cracks expands cracks
How to Prevent and Repair Cracks in Concrete
Talk to your contractor about their curing process. Properly cured concrete is much less likely to crack. Your contractor may ask you to spray down the concrete with water up to 10 times a day for the first week. This is known as moist curing and can greatly improve the strength of concrete.
If you don’t have time to wet the concrete multiple times a day, moist curing will not be an option. Instead, cover the concrete with an insulating plastic sheet or even straw to trap moisture and help the concrete cure at an even rate. Take off the insulating layer and wet the concrete once a day to ensure it stays moist.
If you live in a very cold climate, your contractor may opt to cover the curing concrete with blankets. Yep, cozy cracks. Curing concrete can dry out and crack even faster in cold weather than in warm weather.
Alongside these traditional curing methods, concrete additives and curing compounds can help concrete cure faster and withstand cold weather. After the concrete has fully cured, you can also consider using a concrete sealing compound to improve appearance and reduce cracking.
Final Thoughts on Cracks in Concrete
Don't forget to ask your contractor about how they prevent concrete cracks when pouring new concrete. Of course, you're more likely to get satisfactory results if you choose a concrete company with great reviews from past customers.