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When you see cracks in your home’s slab, you may immediately start thinking the worse: The ground is sinking – or, “Ugh! There’s a sinkhole.”

You may think your foundation is about to give or that you have a really severe plumbing issue. All of these scenarios are possibilities, but more than 90-percent of the time, when you see cracks in your slab, the issue is nothing.

What causes cracks in my home’s slab?

Concrete has a very high compressive strength which is strength gained by forces that “push” or compress something together or withstand loads that will reduce its size. However, concrete has a very poor ultimate tensile strength (UTS), or just  “tensile strength”. This strength withstands forces that attempt to elongate it or try to pull it apart. This property makes it necessary to reinforce concrete with steel rebar so that it withstands the tensile load.

So, enough of our physics lesson today, just know that a lot of different things can cause concrete to crack.

  • Temperature– When the temperature changes, concrete expands when it heats up and shrinks when it cools down, causing cracks.
  • Restraining– When concrete is too confined—like against a structure—and it’s kept from expanding in the heat and contracting in the cold, it can crack.
  • Drying– Concrete goes through a chemical reaction as it cures drying out and causing hairline cracks.
  • Rebar Corroding– Since rebar is steel, it can corrode and expand inside the concrete causing cracks.
  • Settling– With Houston’s soft, clay soil, settling is a constant as homes shift into place. Sometimes, the shift is too drastic and can cause cracks—these create the largest cracks and should be evaluated by a professional.
  • Loading– If concrete is subjected to higher loads than what it’s designed for—like an outdoor kitchen patio with a home-like structure that’s built on an open patio slab—it can cause cracks in the concrete.

Not all concrete cracks are bad.

There are two kinds of concrete: The ones that are cracked and the ones that are going to crack. Sometimes you can see the crack very clearly and, other times, they are so small and narrow that you can’t see them unless you have a strong light or magnifying equipment.

If you’re looking for bad cracks, look for:

  • Cracks that are less than 1/8 inch wide are fine—don’t worry about these.
  • Cracks that are between 1/8 inch and 1/4 inch wide are typically innocuous but could be caused by settling if the concrete on either side has shifted up or down, or side to side. If either is the case, call a foundation expert to at least check it out.
  • Cracks that are a 1/4 inch wide or wider mean that there’s clearly movement and you need to call someone to inspect the area. You probably have an issue.

Keep in mind that wide cracks alone are not indicative of a serious problem. You should see other indicators like sticking or ghosting doors as well as additional cracks around doors and windows.

Often times, minor cracks can easily be repaired with sealant, crack fillers or hydraulic cement. If you don’t know how to do this, ask a concrete expert. For the foundation issues, Church Foundation Repair can give you free inspection and estimate. Most of our inspections don’t result in foundation repairs.