It’s been said there are two kinds of concrete slabs: those that are cracked and those that will crack. In order to have a crack free slab, a lot of things have to come together perfectly. A slab without cracks requires getting the concrete mix right for the temperature and moisture conditions, correctly pouring the concrete, as well as correctly preparing the ground beneath. However, this is not to imply that all cracks are harmless. Their seriousness depends on the type of crack and other considerations.
Whether you’ve noticed foundation cracks when redoing home floors or because of some other reason, the following crack descriptions will help you decide on your next course of action:
Shrinkage cracks occur during the curing process when water in the concrete evaporates. They tend to meander about in crooked lines that branch and fork. They are usually discontinuous in that they will go for a distance, stop, and start again a slight distance away. Hairline shrinkage cracks about 1/16 of an inch wide are harmless.
Small cracks caused by the initial settlement of the soil supporting a foundation slab are usually harmless if the settlement distance is slight, the cracks are small, and the settlement has stopped. The initial settlement of the foundation normally occurs within a three-year period after the house’s construction.
More serious are cracks caused by continuing settlement. Continuing settlement is a long-term process. For example, the clay based soil commonly found in Texas (expansive clay soil) can undergo extensive shrinkage during a long drought. Slab cracks caused by this long-term settlement will get larger and grow in extent. The chances are good that there are cracks elsewhere in your foundation if the process has been happening over a long period. If the cracks are small but your foundation is sitting on expansive clay soil that is settling because of a drought, you can expect the cracks to become a bigger problem in the future. If it’s not addressed quickly, you risk further damage to your foundation.
One characteristic of settling cracks that distinguish them from shrinkage cracks is vertical displacement or sloping among sections of the floor broken by the cracks. Settling after all, involves vertical downward movement of the soil beneath the slab.
Heaving cracks are caused by upward movement of the soil beneath the foundation. Leaking plumbing beneath a foundation slab can cause the soil around the leak to swell especially if it’s expansive clay soil. This swelling then creates heaving cracks. A long rainy period induces the clay soil near and under the edge of a foundation to swell when there is poor drainage.
Telling the difference between settling cracks and heaving cracks is not always easy. A foundation slab that is sinking at its edges during a drought means that the edges will be sinking relative to its center. This can make the center appear to be heaving upward to the untrained eye. Telling the difference between this and a heave caused by a plumbing leak under the center of the slab can be difficult. It’s best to take other considerations into account such as the current weather, your drainage near your foundation, your soil type, and any signs of a plumbing leakage.
While small cracks caused by shrinkage or a small amount of initial settlement of a new foundation are harmless, cracks caused by ongoing soil movement due to either heaving or settling should be resolved quickly. Problems caused by heaving will have different fixes than those caused by extensive settling. This is why getting the correct diagnosis is important. If you are concerned about foundation cracks in your home, contact us at Perma-Pier Foundation Repair for advice or a free evaluation.