Ever wondered why concrete cracks?

We’ve got the answers—and how to fix them!

“All you need to grow fine, vigorous grass is a crack in your sidewalk.” —Will Rogers

While the late great Will Rogers might have had a lighthearted view of concrete cracks, most people dread the sight of them. Fear not! Mathews Readymix is here to help you discover why concrete cracks.

Concrete Sleuthing

Has your concrete suffered a crack attack? Not sure who the culprit is in your construction whodunit? The first step is to figure out what type of crack you have. So get ready, Sherlock! Here’s your list of suspects—and how to catch them:

Crazing cracks

  • Looks like: Small, spidery, thin cracks found on the surface of the concrete

  • Caused by: Premature surface drying due to low humidity, hot sun, or other factors

  • Prevention: Pour concrete during ideal temperature days (50°F or more, without much temperature fluctuation in 24 hours).

Expansion Cracks

  • Looks like: Deep fissures and separated, uneven layers

  • Caused by: Wet concrete running into an object (like a brick wall or a tree) and not having enough room to expand during curing

  • Prevention: Use expansion joints. 

Plastic Settlement Cracks

  • Looks like: Regularly spaced parallel or perpendicular cracks

  • Caused by: Concrete experiencing rapid water loss and/or being restrained by formwork, re-bar, or another obstruction leaving it unable to settle

  • Prevention: Consider using specialty concrete or adding synthetic fibers to the concrete mix, and ensure temperatures for curing are uniform. Then, use a liquid membrane and lay burlap sacks and windbreaks over the top while curing to avoid surface moisture loss.

Weathering Cracks

  • Looks like: Variations in appearance, such as crumbling or tilting

  • Caused by: The ground freezing and thawing, heating and cooling, and expanding and contracting underneath concrete slabs

  • Prevention: Use a mix with a low water-to-cement ratio, and use an aggregate for durability.

If none of those seem to fit your situation, here are some other reasons why concrete may crack:

  • The job site wasn’t prepared properly

  • The wrong ratio of water to concrete was used

  • The wrong kind of concrete was used

  • Rain, snow, fog, or other precipitation interfered with the curing process

  • It was too hot or too cold during the concrete curing process

  • Wind or excess heat caused improper curing

  • Joints weren’t placed properly or weren’t used at all

Address Concrete Cracks

What should you do if you see cracks in your concrete? If they’re thin, superficial ones and the appearance doesn’t bother you, feel free to let it go. But for all other structural cracks, don’t wait to fix them! Depending on the type of crack, you can use a resurfacing product, filler, or mixer. If you have concrete foundation issues, it’s wise to get the advice of a professional—like Mathews! Feel free to give us a call if you have any questions.

Aaron Bacon