Should I worry about hairline cracks in concrete?

Author: Nakia Pfannerstill  |  Last update: Saturday, June 7, 2025

Small, thin cracks usually won't cause any problems and are better left alone. However, if your new concrete develops cracks more than ⅛” wide, it's better to seal them off from water with a high-quality concrete caulk so they don't get worse.

Are hairline cracks in concrete normal?

Before the concrete dries, it's referred to as “plastic,” a particularly temperamental stage. Hairline cracks in new concrete are completely normal because of rapid moisture loss, also known as “plastic shrinkage,” before it dries.

How do you know if a concrete crack is serious?

Cracks that are 0.3 mm or greater can pose an issue for durability and watertightness. This can eventuate into concrete deterioration, affecting its strength and durability.

Will hairline cracks in concrete disappear?

If you had hairline cracks that would be normal for concrete. Since yours have opened that indicates movement. So, unless you can stop the movement (very difficult to impossible) the cracks will reappear and may continue to grow over time.

How much concrete cracking is acceptable?

Evaluating Concrete Crack Severity

Cracks smaller than 0.3 mm in width are generally not serious and of not structural impact. However, they should be monitored for any growth. Cracks of greater width than 0.3 mm may present structural durability issues.

How to fix cracks between ceilings and walls

How to fix hairline cracks in concrete?

You can repair hairline cracks in concrete with a grout made of Portland cement and water. Add just enough water to the cement to form a thick paste. Moisten the old concrete along the hairline crack with water for several hours before adding the grout.

How thin can concrete be before cracking?

Your new layer needs to be at least 2 inches thick. If it's any thinner than that, it'll easily crack under pressure and won't adequately bond to your surface.

Will concrete sealer fill hairline cracks?

Apply a Sealant

Latex or silicone caulking is often a popular choice for crack filling, but the only downside is that the crack will still be visible once it's sealed. Epoxies and concrete sealers are other options, but the sealers will eventually wear off over time.

Are hairline cracks common?

Luckily, most cracks are completely normal in all sorts of houses, even new builds, and are simply a sign that the house is settling. Other causes of cracks include change in temperature or humidity levels and vibrations from traffic if you live near a busy or fast road.

Should you fix cracks in concrete?

Cracks are present in every concrete slab, and they are unavoidable due to the rigid nature of concrete. Uneven drying, shrinkage and temperature changes can all cause fractures in your slab. To avoid water seepage and further damage, it's critical to seal any cracks that develop.

How can you tell if a crack is structural?

Some signs that may indicate that a crack is structural in nature may be that the crack is ⅛” or larger, a crack is horizontal in direction, the crack has shifted forward, one side of a crack projects out further than the other side of the crack, a wall is bowing, and there may be stair step cracks in the mortar ...

What is the width of a hairline crack in concrete?

Although this definition doesn't give a numerical value for width (or require the viewer to wear bifocals to see the crack), it probably applies to cracks less than about 0.003 inch (0.08 mm) in width. Hairline cracks can be very shallow or quite deep, depending on the cause.

Can you pour over cracked concrete?

This means the concrete should be free of cracks, buckling, and breaks. If you notice any small cracks or minor issues, it's in your best interest to repair them before you pour the new concrete. Otherwise, your new concrete will have the same issues.

When should I be worried about cracks in my concrete?

Small, thin cracks usually won't cause any problems and are better left alone. However, if your new concrete develops cracks more than ⅛” wide, it's better to seal them off from water with a high-quality concrete caulk so they don't get worse. You can repair cracks yourself, or hire a professional to caulk the cracks.

Will a thin layer of concrete crack?

The thin concrete layer of overlays, like other thin materials, is more susceptible to cracking than traditional concrete surfaces.

What do concrete shrinkage cracks look like?

Concrete shrinkage cracks are hairline and barely visible. If you see another kind of crack, it probably wasn't caused by shrinkage.

Why do hairline cracks appear in concrete?

Hairline cracks form due to concrete settling while it's curing. They are usually very thin cracks, but they can run very deep in the slab, as well. Because hairline cracks run deep, they pose a risk for more serious cracking once the concrete has hardened.

Should hairline cracks be repaired?

Hairline cracks or cracks under 1/4-inch wide may not indicate serious underlying damage, but if water gets into them and repeatedly freezes and expands, and vehicles continue to drive over them, the cracks can get bigger and the problem can worsen. These cracks can usually be repaired.

What is a normal hairline crack?

Hairline cracks

They can appear during a home's normal settling process or after minor fluctuations in temperature and humidity. Hairline cracks can run in any direction and don't require immediate attention.

Are hairline cracks in concrete foundation normal?

Some cracks in the foundation, including hairline cracks, are considered normal foundation cracks. These typically appear due to settling or concrete shrinkage. Other types of foundation cracks might indicate a serious structural problem.

How to prevent hairline cracks in concrete?

With some key preventive measures like the ones mentioned below, propagation of cracks in the concrete can be restricted:
  1. A lower water to concrete ratio leads to higher strength and lesser cracks.
  2. Good quality aggregates should be used to lower shrinkage in the concrete.

Why is my brand new concrete cracking?

Shrinkage Cracking

As the concrete begins to dry, the water within evaporates, and as it does, the concrete will begging to shrink. A concrete slab will shrink about ¼ inch for every 100 square feet of surface space. When concrete dries and shrinks, cracking can occur hours after being poured.

Can I put Quikrete over existing concrete?

QUIKRETE® Concrete Bonding Adhesive (No. 9902) permanently bonds new concrete, plaster, and stucco to existing concrete, plaster, and stucco. Eliminates the need for roughing the surface before the application.

Does wetting the concrete stop it from cracking?

Moist curing is a common method of concrete curing. It involves wetting the concrete slab often with water (5-7 times per day) for the first 7 days. This method ensures your concrete slab will be extremely strong and durable, because it allows the moisture to evaporate slowly, preventing cracks and shrinks.

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