Living and working in concrete every day, this is perhaps one of the most common questions that we get asked. Okay, so we don’t technically get asked this question word for word, but we do get asked, “why did my concrete crack?” and “I don’t understand, we just had this concrete installed a year ago and it is cracking already”. So, similar questions to the title of this anyway.
More often times than not the home owner believes that the work they might have received was shoddy and that led to the concrete cracking. Ultimately this could be true, it is important that concrete contractors follow the very well established instructions and guidelines when installing concrete. This often times does not happen.
Concrete can crack for several different reasons, the main reasons for cracking are:
- Too much water or excessive slump in mix
- Concrete dried too quickly when setting
- No saw cuts or control joints
- Concrete poured and set on frozen ground
- Improper strength of concrete for installation
This is not the comprehensive list of why concrete cracks as there are is undoubtedly endless reasons for why concrete can crack; however, the conditions listed above are most common.
Too much water in the initial mix
Often times in residential concrete, the mix is much different than what is used on commercial projects. According to the concrete network, often times concrete mix that is used on residential projects is quite simply much too diluted or there is excess water. This excess water greatly reduces the integrity of the concrete or in other words decreases the strength of the concrete.
The biggest reason for cracking is because concrete shrinks as it hardens and with wetter concrete or “superior” mix, the shrinkage will be more significant. The effect of this is that the shrinkage really forces the concrete slab to literally pull apart and at the end of the day the cracks are the end result of all of these forces. What is important is that a mix be created properly from the beginning with a low water to cement ratio. This is the number one issue which affects the quality of your concrete.
In order to make sure that your concrete is mixed properly it is important that you choose either a reputable concrete contractor to complete your project or that you really perform some due diligence when deciding who to order your concrete from.
Concrete sets too fast
If the concrete cures to quickly this will increase the chances of your new concrete slab cracking as well. The chemical reaction which actually causes your concrete to go from a liquid state to a solid-state requires water. It is important that your contractor has the right amount of assistance in finishing your concrete properly. There are different methods that your contractor will use to ensure that the concrete is cured properly.
Improper strength of Concrete
If the improper strength of concrete is used for the job then concrete can crack. For example, if anything less than a 4000 psi is used for a driveway, the concrete can definitely crack. Often times a higher psi strength concrete is recommended for driveway installations. It is important that you get the manufacturer’s recommended strength for the appropriate use. Your concrete contractor or local ready mix operator should be able to tell you what the appropriate strength is for your particular application.
Concrete is inevitably going to crack and so directing where that cracking is going to happen can help the entire slab live a longer life. Control joints should be cut the depth of the concrete slab and should happen every two times the thickness of the concrete. So for example if we take a traditional 4 inch installation times two (in feet), we would install control joints every 8 feet for this particular example. If we were installing 6 inch concrete we could install control joints every 12 feet instead.
Improper pouring conditions
Installing concrete onto frozen ground, this does not mean that concrete cannot be installed during cold weather, it can. This means exactly what it says, concrete should not be installed on frozen ground which means that proper precautions should be taken to make certain the job is handled correctly.
Installing concrete on frozen ground means that the concrete will actually cure as the frozen ground thaws. As the ground settles from being frozen your concrete will be susceptible to cracking. The concrete was wet when you installed it and installing wet concrete on a cold surface will lead to longer setting times which will also lead to your concrete cracking.
By addressing these issues upfront with your contractor or making sure these issues are addressed can help you install a more reliable product from the beginning. Take the time to study proper concrete installation before attempting to install yourself or working with a contractor can help you save a great deal of time and will assist in a successful installation from the beginning.