Why Do Concrete Slab Foundations Crack?

If you’ve ever tried looking for information on concrete cracks, you know it can be tough to find. There seems to be a lot of theories and not enough facts. What causes concrete to crack? How do you repair the foundation? Why do concrete foundations fail in the first place?

This article will answer these questions and help homeowners identify and resolve the common causes of cracks in concrete slab foundations.

Why Do Concrete Slab Foundations Crack?

What Causes Concrete Slab Foundations to Crack?

There are many reasons why slab foundations crack. The most common reasons are as follows:


The most common cause of cracks in foundations is shrinkage. Shrinkage occurs when water evaporates from the surface of the concrete, leaving behind air pockets that expand and push the surface apart from each other.

The process repeats itself until the concrete has dried completely and there are no more air pockets left in the slab.

Poor Construction

Improper construction can also lead to foundation problems. If your builder did not use proper building techniques, then your home may have issues with cracking and settlement.

If your home was built on uneven ground, it may also experience foundation problems such as cracking and sinking due to poor construction techniques.

Poor Soil Conditions

Another reason for foundation cracks is poor soil conditions. The ideal soil for a slab foundation should be able to support the weight of the structure it bears without compaction or settlement.

If your soil cannot support the load without settling, it will crack under pressure from your home’s weight.

Improper Compaction

Improper compaction of concrete is the most common cause of foundation cracks. When concrete dries out, it contracts. This contraction can cause cracks in your slab if it’s not properly compacted during construction.

If there is more water used than cement or sand, the concrete will be weak and spongy. If there is too little water, the concrete will be hard and brittle. The ideal consistency for concrete should be about three pounds per gallon (4,000 psi).

Improper Slab Thickness

If the amount of material used to form the slab is insufficient, cracks may form on the concrete’s surface. The size of the slab will vary depending on your building code and local regulations.

In most cases, this is not an issue because most contractors follow accepted standards when installing slabs. However, if you’re building your own home and use unapproved methods, this could be one reason why your house has developed cracks in its foundation.

Tree Roots

Tree roots are one of the most common causes of foundation cracks. As trees grow, they send out roots that search for nutrients in the soil below ground level.

If these roots find themselves growing through an area that is made up of a weak material such as concrete, they can end up causing problems for homeowners. This makes them likely candidates for damaging your home’s foundation if given the chance.

How to Fix Your Cracked Foundation

If you have a cracked concrete slab foundation, Hargrave Custom Foundation Repair is here to help! We will provide consultation on what your options are for repair and how to determine the best repair method for you.

Give us a call today to schedule your foundation inspection or concrete repair service!