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Are Slab Foundation Cracks Normal? (Guide to Slab Foundation Repair)

It’s common to see shrinkage and cracks in a slab foundation, and they may not be something to worry about because the structural integrity of your house may not be compromised. When you notice that your trim, wood framing, and wood floors are shrinking, it may be due to humidity. This shrinkage may just be a way to acclimatize to lower humidity within your home. In the same vein, your slab foundation can go through seasonal expansion and contraction due to temperature changes.

In this article, we discuss the different kinds of cracks your slab foundation may experience, when you should be bothered, and how to go about slab foundation repair. Our team can complete a foundation inspection in Oklahoma City.

Is it common for slab foundations to crack?

Homes are usually given a soil movement allowance of about one inch. In areas where the soil is highly expansive, the slab foundation can be given a 4-inch soil movement allowance. Foundation movement also makes the structure move and results in a degree of racking, distortion, and cracking.


That said, a foundation must be designed to maintain structural integrity. However, cracks can be normal.

Slab foundation cracks

The major reasons behind the popular use of concrete in foundations are its strength and durability. However, it is not foolproof. The following are some of the common cracks that affect slab foundation:


  • Hairline cracks: These types of cracks mainly occur as a result of the concrete settling while it cures. They can be extremely thin, but deep. A deep hairline crack can get wider with time and the crack can become worse inside the slab.
  • Crazing: These cracks are shallow and do not result in very serious damage. Crazing is also caused by uneven drying during the curing process of the concrete.
  • Plastic shrinkage: The major cause of this can also be traced to an incorrectly cured concrete. In this case, the surface of the concrete dries faster than the inner parts of the slab. A typical plastic shrinkage reaches through the middle of the concrete. They also appear to occur across the concrete surface at no particular pattern.
  • Durability cracking: It takes many years for these kinds of cracks to form, usually beneath the slab’s surface. They are usually caused by the repeated cycle of moisture freezing and thawing inside the foundation. The resultant effect of this is that the concrete is weakened and the cracks start getting visible on the surface.
  • Scaling: When concrete is not well protected from water, over time, it starts to absorb the water. This forces the concrete to expand as the temperatures become freezing. Also, this expansion can be caused by air pockets trapped close to the concrete’s surface. This eventually causes some parts of this surface to crack and pop out, thereby causing small and shallow blisters on the concrete surface. This could be an indication of a crack in the slab foundation.
  • Offset cracking: These kinds of cracks are usually due to unevenness in where the slab itself is sitting. Some common causes of this include poorly compacted subsoil, the rebar being repeatedly expanded and contracted, tree roots invasion, or failure to remove previously installed concrete slabs. 

Fixing a crack in a slab foundation

If we’re talking about a few shallow cracks in your slab foundation, then you may be able to fix them cosmetically. But of course, you have to first identify the cracks. The question you must ask is: are you sure the seemingly thin cracks are not signs of more serious problems in your foundation? That is why you should leave the repairs to a professional slab foundation repair. 

So, before you jump into fixing the cracks in your slab foundation, you want to be sure of the magnitude of what you’re dealing with. Again, the best person to tell you exactly what’s wrong is a professional foundation contractor.

 Furthermore, if you’re dealing with very many small cracks or the cracks are wider than a quarter of an inch, then you will be needing the service of a structural engineer. In severe cases, the expertise of a geotechnical engineer may be required to address more fundamental issues.

Final thoughts

Not every kind of crack in your slab foundation is a cause of alarm. However, you don’t want to be negligent. The thing to do once you see any sign of a foundation problem is to call a reputable slab foundation repair contractor. This will help to prevent the problem from getting worse with time.

And, you don’t have to wait till you see signs. Scheduling a periodical inspection of your foundation can keep you out of serious foundation issues. Just make sure you’re hiring a reputable professional to fix whatever is wrong with the slab foundation. So, do due diligence why checking the slab foundation repair contractor’s rating on the Better Business Bureau.

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