Main Reasons for Cracks in Concrete Floor and What to do About It

You’re all excited that you have finally moved into your brand-new home and gotten everything settled. Imagine your shock when you walk out to your car and find a massive crack on the garage floor in the concrete! It has only been a few months since your contractor finished your home and now you must deal with the cracked concrete.

Garage concrete floors crack – period. As we all know, concrete is not like a ductile material, and so it neither bends nor stretches without breaking. However, it does expand and shrink with temperature changes, resulting in the cracks you are now seeing in a newly built home. While it may indicate foundation problems, that is not always the case. Garage floor cracks are common and not necessarily a warning of serious structural issues. Concrete Contractors see these situations all the time and, in some situations, a homeowner can easily repair the cracks by themselves. Before you do any repairs on the crack, you need to know what has caused it in the first place.

So, let’s first understand the reasons that the concrete floor in a garage may develop cracks, and thereafter discuss what to do if you have what it takes to repair it.

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Common Causes of Cracks in a Garage with a Concrete Floor

1) Home foundation has settled

In the first one or two years, a newly constructed home will have its foundation undergo some changes that may make the garage floor settle a bit. One possible reason for settling is if a massive tree is removed from the spot near the concrete slab, the unseen roots or buried roots will eventually decompose. The decomposed roots cause a void and cause the foundation to settle a bit and the concrete to develop some cracks. Sometimes referred to as subsidence, settling is common over trenches where plumbing pipes and utility lines are buried. Often, the said trenches are not compacted when refilled. When an unsupported concrete slab is placed atop a poorly compressed trench, the void created by settling can cause a crack across it.

Read more: Buying a house with a cracked foundation

2) The concrete had too much water in the mixture

While most concrete contractors know that too much water in the concrete mixture does not result in an optimally strong slab for garage floors, many of them still repeat the same mistake! They believe that if excess water is added to the concrete, it makes it easier to install. However, that is far from the truth, and in fact, the prime suspect for cracking in garage floors!

Cracking resulting from adding excess water in the concrete mixture is called plastic shrinkage cracks. Before the concrete hardens (in a plastic state), it is full of water, which takes up lots of space and increases the size of the concrete slab. As soon as this slab loses the excess moisture, it shrinks. As it shrinks, it drags the granular sub-base creating stress that pulls the concrete apart. If the stress becomes unbearable for the now-hardened concrete, cracks begin to develop to relieve tension.

Read more: Why does my concrete patio sweat?

3) Concrete slab dried up too quickly

Rapid drying of the slab is another factor that causes the development of cracks on a concrete garage floor. There are two types of cracks under this cause: crazing cracks and crusting cracks. The latter type occurs during the stamping process of the concrete. It typically happens on windy or sunny days when the top-most section of the concrete slab dries out faster than the bottom. The result is that the top becomes too crusty and so when the stamp is embedded, it quickly pulls the surface apart and causes small cracks at the concrete slab edges.

The former type of crack, crazing, is a fine crack that appears like a shattered glass or spider web. This happens on a concrete slab when the topmost section loses water too quickly.

4) Overloading the concrete slab

Another reason why garage concrete floors crack is placing too much weight atop the slap. Even though concrete is a very strong material, just like any building material, it has a load capacity limit. Therefore, if the PSI weight is too excessive for the ground underneath the slab of concrete to carry, it will typically crack. This is true especially after long periods of snow-melt or rain when the ground is soft and saturated. Cracks of this nature occur because the flexural strength of the concrete slab is less than the compressive strength, making the slab twist to its breaking point.

What can you do about the big crack?

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Of course, if the crack is too big, you may need to get the assistance of concrete contractors. However, if you have the knowledge and a few skills, then you can repair it by yourself. The good news is that the repairing process is simple and straightforward. First, chisel out the cracked zone with the intention of making a backward angle. Secondly, clean out all the loose material. Third, pour some sand into the crack to within a few inches from the surface. Fourth, get a concrete fortifier and prepare a sand-concrete mix. Finally, fill in the crack and feather out until you have a new level ground concrete.

Read more: Bringing Your Garage Floor To Life With Epoxy Coating

Ways to minimize major cracking in concrete garage floors

They say, an ounce of prevention is better than a pound of cure, and so minimizing major cracking in concrete garage floors is highly recommended. To be proactive about taking care of your concrete slab garage floor, here some of the tips you need to do:

Use control joints

Since engineers and contractors are aware that most concrete slabs are going to crack, they tend to control where it is most likely to crack. This is achieved by placing something called control joints in slabs, often ten to twenty feet apart and in all directions. Control joints allow for movement caused by drying shrinkages and temperature changes. This gives contractors an active role in deciding where they want the slab to crack if the concrete gives in!

Read more: When to remove concrete patio slabs

Carefully control the amount of water in the mixture

We explained earlier that too much water in the concrete mixture contributes significantly to garage floor cracking. The best way to prevent cracking of this kind is to observe low water to cement ratios.

Read more: How to remove moisture from walls

Adequately cure the concrete to avoid it drying out too fast

Properly cured concrete slab increases durability, strength, wear resistance, and water tightness. Care should be taken when curing to avoid drying out too fast. It is advisable that the slab is ponded, flooded, or mist sprayed. Otherwise, make use of effective water retaining options like covering with sand, straw, burlap, or canvas to ensure it continuously remains wet. As soon as the concrete slab is hard enough to resist any surface damage, a plastic film seal or waterproof paper is applied.

If you find yourself in the position of needing a crack repaired in your garage floor, be sure to contact us and we will take care of your needs!

Read more: Decorative Concrete Floors: A Comprehensive Maintenance Guide

Written by Terry Smith. December 27, 2018

Terry Smith is the owner of Concrete Contractors of Killeen. Having operated in the concrete industry for over ten years offering everything from residential to commercial concrete, his business proudly serves Killeen and the surrounding areas for all concrete projects and needs.