Concrete-wise, cracks are no joke (See what we did there). But really, concrete has a tendency to crack, however the reasons vary. Some people will tell you that it is inevitable, that all concrete slabs will crack. A lot of times, it seems this is true, but why does concrete crack? A lot of homeowners will question the quality of work when their newly laid concrete cracks. The main reason concrete cracks is due the concrete shrinking as it hardens. Cracks also happen due to the way the concrete settles and other times cracks happen from other reasons. When concrete is properly installed it is one of the longest lasting and most durable products you can utilize in your home. There are well established guidelines when it comes to the placement of concrete that any well-experienced and skilled contractor should know. Creating crack resistant, strong, and durable concrete is a skill set itself. Let’s review some of the more preventable possibilities for why concrete cracks.
The first reason for concrete cracks is too much water in the mix. Not much water is required for concrete to achieve maximum strength. Often too much water is added to concrete on jobsites. When extra water is added deliberately it is usually to make the concrete easier to install. However, excess water can greatly reduce the strength of the concrete. Remember that we mentioned that cracks happen mostly because of concrete shrinkage. This is because of the excess water evaporating from the concrete. The wetter the concrete mix, the more the concrete will shrink. Slabs of concrete can shrink up to ½ inch per 100 feet. Force from the shrinkage causes the concrete slab to be pulled apart, which is where the cracks come from. To prevent cracking from too much water, make sure you know the allowable amount of water for the mix.
Rapid drying of the concrete is another reason that concrete cracks. Rapid drying increases the likelihood of the slab cracking. There is a chemical reaction when the concrete dries that allows it to transform from a liquid to a solid. This is due to hydration, which continues for weeks after the concrete is poured. It is important to make sure that the concrete cures properly by making sure that adequate water is available for the hydration reaction.
Another reason for cracks is improper strength of the concrete used on the job. Concrete comes in multiple strengths. Make sure that you know what strength the job requires. You can talk to the ready mix supplier to guarantee that you are using the proper strength.
One of the other most commonly seen reasons for cracks in concrete are the lack of control joints. Control joints allow the concrete to crack where you want it to. Control joints should be the depth of the slab and up to 2-3 times (in feet) of the thickness of the concrete in inches. This means that 4 inches of concrete will have joints 8 to 12 feet apart. (To learn more about control joints click here).
One last note for preventing cracks is to never lay concrete on frozen ground, the ground that the concrete is laid on must be compacted. The ground must be properly prepared according to the soil conditions. While some flatwork can be laid right on top of native grade, in some other areas six inches of base fill and steel rebar is required in the slab.
At Custom Concrete Creations we have state of the art equipment and a properly trained team with years of experience. Custom Concrete Creations is a premier contractor serving the Omaha area as well at the Midwest. Give us a call or send us an email for your custom concrete finishing needs today!