Concrete is durable and long lasting surface covering, but it can crack if not installed properly. But how do cracks in concrete happens and are they dangerous? Find out below.
How Do Cracks In Concrete Happen?
There are various causes of why concrete cracks. This mostly has to do with the outside elements (weater, wear and tear), and how the concrete was set up.
Why Does Concrete Crack?
Concrete cracks due to a number of different factors, including:
#1. The installer poured the wrong strength concrete for the slab.
There are different strength concrete mixes available so make sure to choose the one that can handle its useage after drying and setting up. If you are a beginner at installing concrete, check with your mix supplier to get a clear idea of which to use.
#2. Too much water was added to the mix.
Most people don’t realize that concrete does not require very much water to reach its ideal strength. Many isntallers are not experienced enough to know what ammount of water to add. Although it makes the concrete easier to pour, it weakens it. This is because as the concrete dries, the water evaporates which will shrink the slab and produce cracking.
To avoid this, check the mix package and talk to the supplier as to how much water to add. A general rule of thumb is a half pound of water for every pound of cement, which is called the .5 ratio.
#3. The concrete dried too fast
If a slab of concrete dries too fast, it increase the chances of cracks forming. This is due to the decrease in water available to the concrete as it sets over hours and days.
#4. Not enough control joints were included in the slab
Control joints allow the concrete to focus cracking and shifting only at certain points. If you do not have enough of them, or wide enough joints, then the concrete is more likely to crack. Make sure the joints are the thickness of the slab, and ~3 times the the thickness in terms of the joint width.
#5. The concrete was poured on frozen ground
Pouring concrete onto frozen ground, snow, or ice could lead to the concrete cracking. This is because the ground will eventually thaw, causing it to settle, which will leave the concrete sitting above the ground.
#6. The ground that was not compacted properly
The soil you are pouring the concrete over will have certain characteristics. Some ground can accept concrete poured directly on it, while other soils need to be compacted, base filled, and steel rebar inserted in the slab.
#7. Expansion due to hot weather
During hot weather, a concrete slab will expand slightly. If there is an object pressing against the side of the slab, the concrete could crack as the pressure builds. The key here, is making sure the concrete has a little bit of room on the edges to expand over time with the changing weather.
#8. The ground moves or shifts over time
Ground shifting can easily happen if there are large trees nearby that have grown their roots deep and wide. This will push the concrete upwards which will lead to cracking. The ground could sink or shift due to an influx and drop in water levels which will also cause the concrete slab to crack. Most often, this process occurs in residential neighborhoods along sidewalks and old driveways.
#9. Too much weight is put on the concrete
This is called overloading and can cause the concrete slab to crack or break. Driving a car over a sidewalk or having a moving van parked on a driveway could be too much weight for the concrete to handle.
How To Repair Cracks In Concrete
All types of concrete can crack, and unless reinforced and placed on solid, unmoving ground, will over time. Some types of cracks are easier to fix than others and you can try to do it yourself. However, calling a professional to do it, especially if you are unexperienced might be the best idea. They can also tell you if the concrete is repairable or should be replaced.
Types Of Concrete Cracks
Concrete cracks come is variety of types, including:
- Structural cracks – are long cracks that may require the slab to be replaced.
- Cracks due to settling – happens when the ground settles below the slab.
- Hairline cracks – small cracks that are easiest to repair.
- Cracks due to shrinkage – appear when the concret cures and shrinks.
Risks Of Cracks In Concrete
What are the chances that cracks in a concrete slab will appear?
There is always a possibility that concrete will crack, atleast in small ways. Most often, these are cosmetic and do not cause much health risks to people walking on it. However, the dangers are heightened on sidewalks and driveways that have extensive and wide cracks as this can cause injury.
The size of the crack matters, and it is up to the person inspecting the concrete to decide if it needs reparing or not. There is no hard and fast rule as to when a crack needs filling. Individual owners of concrete driveways and floors may be in more of a hurry to fix or replace a concrete slab than a contractor, engineer or architect would be because they have to engage with it each day.
Generally speaking, concrete cracks that are wider than hairline cracks are likely structural and are signs of bigger problems.
Concrete Crack Filler – Does It Work?
This all depends on the type of concrete crack filler used. Some effective crack fillers include:
- Flexible concrete crack filler
- Pre-mixed concrete patch
- Hairline crack sealer
- Liquid cement crack filler
- Concrete two part epoxy
- Hydraulic cement
Why Are Cracks In Concrete Bad?
Cracks in concrete are not always bad, but when they are it is due to the risk of causing injury or harm to a person or vehicle. Aesthetically speaking, cracks in concrete do not look great, and weeds and debris could build up in them, ruining the slab’s appeal.
If the cracks are wide enough, you could drop something small (car or house key) into one and lose it.
Cracks in concrete also may be harmless at first, but they will allow water to seep below the slab which could allow the soil to move, making the cracks worse over time.
If cracks are not repaired, then eventually, cars and bikes will wear down the broken parts of the concrete and turn it into dust and gravel. At this point, the slab will need to be replaced.
Cracks In A Concrete Floor
This certainly does happen, and is likely caused by curing, shifting ground beneath the slab, and weight placed on the concrete over time. The end result is a drop in its aesthetic value.
Cracks In Concrete Bathroom Floor
Most people install lenoleoum or tile flooring in their bathroom. However, concrete floors in homes have become fairly popular recently. A downside is the possibility of cracking, and rather than being able to switch out a tile or two and filling in the grout, the floor is left with noticeable cracks.
Cracks In Concrete Kitchen Floor
Concrete for kitchen flooring is a popular way to go, but presents the possibility of cracking. This is especially true in this part of the house due to the very real chances of dropping heavy pots, pans, and kitchen appliances onto the floor. Over time, this can cause cracking in the concrete. Kitchens also are places of meeting guests and cooking meals each day, which gives them a high ammount of foot traffic. Shifting or moving refrigerators or stoves, which are very heavy, can also possibly cause hairline cracks in the floor.
Cracks In Concrete Garage Floor
Most garages have concrete floors because the builders do not need to spend time making it aesthetically pleasing, just functional. A concrete garage floor needs to be able to hold the weight of a car, tools and equipment. All garage floors have rebar included which allows them to hold large ammounts of weight.
People sometimes choose to carpet their garage floor or add wood boards or foam padding to the surface to prevent cracking.
Cracks In Concrete In Summertime
If a slab is already long dried, then the heat should not affect it as much. If you pour concrete in hot weather, the water in the mix could evaporate faster which can lead to cracks. It may be best to poor concrete in the springtime of fall, or towards the afternoon, so it can dry overnight when the termperature drops.
Cracks In Concrete In Wintertime
Ice due to extreme cold, and the weight of heavy snow can cause cause cracks in concrete slabs. Adding rebar to the concrete and extra control joints will help prevent cracking. It is best not to pour concrete in extremely cold weather, as the mix could freeze and the curing will be delayed. Once the weather warms, the slab will shrink, and so will the ground beneath it, causing cracking.
Concrete is a very strong and durable material that can last with proper installation and treatment. If you find cracks, make sure to assess them for possible risks to yourself or your vehicles and repair them if possible.
Nick Klamecki is a certified Fire and Workplace Safety expert with 15 years experience in product research and testing. He has a degree in Economics from U.C. Davis, is an active outdoorsman and spent years ensuring the safety of special needs children. Nick researches and tests workplace, industrial and safety products and provides advice on their safe use.