Common Types of Cracks in Fresh Concrete

Concrete might seem strong and unbreakable once it hardens, but during its early stages, it’s a lot more delicate than most people think. Fresh or “plastic” concrete still has a lot of water inside, and it hasn’t developed its full strength yet. That’s why cracks sometimes show up on brand-new sidewalks before the concrete has even finished curing.

The key is knowing which cracks are just surface-level and which ones could cause bigger problems later on.

Let’s take a closer look at the most common types of cracks in concrete, why they happen, and when you should start worrying.

Plastic Shrinkage Cracks

Plastic shrinkage cracks are the most common type you’ll see in new concrete. They form when the surface of the concrete dries out too quickly. As the water evaporates, the surface starts to pull apart, kind of like how a mud puddle dries and splits on a hot, windy day.

These cracks are usually thin and shallow, spreading out in random, web-like patterns. While they don’t always go deep, they can make the surface weaker. If water or chemicals seep through them, they can shorten the life of the concrete.

The good news? These cracks are easy to prevent. Proper curing, covering the surface, or slowing down evaporation in hot or windy weather can make a big difference.

Should you worry? Not always. If the cracks are fine and shallow, they’re mostly cosmetic. But if you notice them spreading or getting deeper, it’s best to call a concrete expert to take a look.

Plastic Settlement Cracks

Settlement cracks happen when parts of the concrete sink while it’s still soft. This usually occurs because the heavier materials inside, like gravel or steel reinforcement, settle unevenly. When that happens, the surface gets pulled apart, leaving visible cracks.

These cracks often appear directly above reinforcing steel or where the slab’s thickness changes. Unlike surface-only cracks, settlement cracks can run deep and expose the steel to moisture. Once water reaches steel, rust and corrosion can begin, which leads to long-term damage.

What to watch for:

If the cracks line up with reinforcement patterns or appear long and straight, they could be serious. Sealing them early can help, but if they’re deep, it’s smart to get professional advice before the problem grows.

Thermal Cracking

As concrete hardens, it gives off heat through a natural chemical reaction. In smaller pours, you might not notice, but in large slabs or foundations, that heat can build up. Later, as the concrete cools, it shrinks. If one part cools faster than another, the tension can cause cracks; these are known as thermal cracks.

You can think of it like what happens to sidewalks on a cold winter morning after a warm day;  the sudden temperature change makes them expand and contract. The same process happens inside when curing concrete.

Should you be concerned? Not always. Many thermal cracks are minor and can be controlled with good design, for example, by adding control joints in the right places. But if the cracks are wide, deep, or growing, they can let water in and lead to damage from freezing and thawing cycles. Catching them early helps prevent that.

Construction or Restraint Cracks

Sometimes cracks appear because the concrete can’t move freely as it sets. This is called a restraint crack. It happens when new concrete is poured against an existing wall or tightly enclosed in forms that prevent it from shrinking naturally. When that tension builds, cracks form as the concrete tries to release the stress.

Restraint cracks usually appear where new concrete meets old or where the shape or thickness changes suddenly. These aren’t just surface cracks; over time, they can grow and let in water, salt, and other materials that slowly damage the slab.

Here is how to prevent them:

Proper reinforcement, well-placed joints, and thoughtful design can minimize restraint cracks. If you already see them, sealing and monitoring them is important to prevent further damage.

Drying and Early-Age Shrinkage Cracks

Even after the concrete has set, it continues to lose moisture over time. This process, known as drying shrinkage, can cause cracks if the concrete wasn’t cured properly. Unlike plastic shrinkage cracks that appear right away, these take a little longer to show up.

You’ll often see them as wider cracks stretching across larger parts of the slab. Sometimes they’re straight; other times, they wander randomly. If ignored, they can turn into trip hazards or let water seep through, which can weaken the concrete.

Curing is everything. Keeping the surface moist or using curing compounds helps concrete retain enough water to gain full strength. Skipping or rushing this step is one of the most common reasons for drying shrinkage cracks.

When Do Cracks in Fresh Concrete Really Matter?

Here’s something most homeowners don’t realize: some cracks are perfectly normal. Almost every new concrete slab will crack a little as it settles and dries. The question isn’t whether it cracks; it’s whether those cracks are harmless or signs of a deeper problem.

Hairline cracks from plastic shrinkage are usually cosmetic. But settlement cracks, restraint cracks, or thermal cracks that grow wider or follow a straight pattern could affect the slab’s strength and durability.

A good rule of thumb: if the cracks are spreading, collecting water, or lining up with reinforcement, it’s time to have a professional inspect them. Fixing problems early is far cheaper than waiting for serious damage.

Conclusion

Concrete needs time, usually about 28 days, to reach its full strength. During that time, proper curing and care are crucial. Cracks can happen, but understanding what causes them helps you tell the difference between normal settling and something more serious.

Some cracks are just part of concrete’s natural behavior, while others can lead to long-term problems if ignored. The best approach is to keep an eye on your sidewalk and address issues early. Concrete is meant to last for decades, as a little attention now ensures it actually does.