Are Hairline Cracks in a Concrete Slab Normal?

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    It is every property owner’s nightmare: a crack in a concrete slab. But is this hairline crack a minor blemish or a sign of an impending major problem? 

    Thankfully, hairline cracks in a concrete slab don’t always indicate major foundation issues. It is still important to take them seriously and evaluate each crack on an individual basis. Left unchecked, structural cracks in concrete slabs can spiral into major problems.

    Here’s what you need to know about cracks in a concrete slab, including when to call in professional support.

    What Causes Cracks in a Concrete Slab?

    There are several main causes of concrete slab cracks. Some occur during the construction process, and others occur over time. The most common causes of cracks in a concrete slab after construction has been completed are:

    • Expansion
    • Heaving
    • Excessive Weight
    • Settling
    Cracks in concrete slab

    What Are Expansion and Heaving?

    Concrete is actually a porous substance where water can settle in small holes or channels on the surface and throughout the slab. In heat and cold, moisture in these holes and channels can expand and contract. 

    In the summer months, heat can cause concrete to expand. If there are no expansion joints between surfaces (such as the rubber strips you may see between sidewalk slabs), the concrete may push against something that cannot flex. As a result, the concrete slab has nowhere to expand and will start to crack.

    Heaving can also be related to temperature changes. Unlike expansion, which occurs in warm weather, heaving can occur when the ground freezes and thaws, lifting and settling the concrete. After many cycles, the concrete may develop cracks. 

    Tree roots pushing up underneath a slab can also cause heaving cracks to develop over time.

    How Do Excessive Weight and Settling Create Concrete Slab Cracks?

    Although concrete is tough, it is not indestructible. Excessive weight, from a dumpster, recreational vehicle, or another heavy object, can cause cracks to occur in a concrete slab.

    Settling occurs over time when the ground beneath a slab shifts or is altered, creating a void between the ground and the bottom of the slab. Without ground to support the weight of the slab, the slab’s own weight causes cracks to appear on the concrete’s surface.

    Vibrations from site prep nearby can cause the soil under finished construction to settle. Removal of trees can cause roots under concrete slabs to decay and leave a void where settling can occur. 

    Settling cracks are extremely common and do not always present a threat to a building’s foundation.

    What Are the Main Causes of Settling Cracks?

    For property owners, the most common form of concrete slab cracks come from the settling of a house or building over time. These cracks can be structural (ones that threaten a building’s structural integrity) and non-structural (ones that are cosmetic in nature, but can evolve into structural issues).

    Concrete slab cracks from settling are caused by a variety of reasons:

    • Type of soil: Soil that contains clay swells and shrinks depending on moisture levels, causing movement to the slab
    • Poor drainage and erosion: Water around the foundation can cause hydrostatic pressure cracks, and erosion of soil can lead to space underneath a slab
    • Underground water leaks: A leaking or ruptured pipe can create a void underneath a slab, leading to cracks
    • Earthquakes: Although rare, earthquakes can cause shifting of the soil underneath a slab or directly crack the slab from the sudden movement

    At a glance, it can be difficult to tell whether a concrete slab crack is cosmetic or related to a foundation problem, especially if you do not know what is causing the crack.

    How Do You Know When to Call in a Professional for Foundation Repair Services? 

    The key factors to keep in mind when looking at concrete cracks are:

    • Size
    • Number
    • Location

    In general, hairline cracks are not often a structural problem. However look for cracks that are wider than 1/8 of an inch, cracks that are wider at one end than the other, cracks that extend a long distance across the slab, or cracks that increase in size over time.

    Cracks that continue to increase in size indicate the potential of an ongoing problem and should be examined. Larger cracks should be looked at, as moisture can settle in these cracks, leading to structural damage.

    For hairline cracks, it is not uncommon to see a few develop in a slab over time. Some may even occur during the concrete curing process if the concrete is too wet, dries too quickly, or is exposed to significant extremes in temperature.

    If you notice that the number of hairline cracks is increasing over time, this may indicate a foundation problem and should be examined by a professional in concrete crack repair.

    The location of a crack can indicate whether it is a problem or not. If it is located in an area that sees a lot of weight pressing down and being removed, harmless hairline cracks in the concrete slab can develop over time.

    On the other hand, cracks that occur from the concrete slab and run up to windows, create stair-step cracks along the edges of brick, or form gaps near doors can indicate a larger issue. Even if the hairline cracks themselves are not an issue, combining with other cracks that can allow water intrusion can make them a long-term problem.

    Who Can You Contact If You Suspect Foundation Issues?

    When it comes to hairline cracks in a concrete slab, although many are harmless, getting a professional opinion can provide peace of mind. Additionally, the earlier you catch a foundation problem, the easier it is to mitigate damages.

    For residential or commercial building foundation repair services and foundation maintenance services in Northern Virginia, contact the professionals at LUX Foundation Solutions. From hairline cracks to major slab issues, LUX Foundation Solutions can evaluate foundation concerns provide professional repair services. 

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