Cracks in a concrete garage floor may indicate that there are foundation problems or other issues. As buyers or owners, we want to know how to tell if they’re serious; basically when to worry.

The good news is that most cracks in garage floors are common and not an indication of serious structural issues. However, there are a few that indicate that maintenance is needed or that there may be a structural concern.

Some of the most common reasons for cracks in garage floors are settlement, shrinking, improper installation, and poor drainage. In some cases, cracks are nothing to worry about. After all, one thing is for certain when working with concrete, and it is destined to crack at some point. You can tell if cracks in your garage floor are serious if they have an opening that measures 1/8-inch or more in width, and/or if one side of the crack is higher than the other.

Learning how to repair a garage floor doesn’t have to be as scary as it sounds. You may be surprised to learn that many repairs can be done easily by yourself and for less expense than you think. Typically with a garage floor, there are three types of repairs that are the most common; surface cracks, pitting and spalling. Pitting and spalling can be just as easy to repair as most cracks, it just takes a little more work.

If you are applying a sealer, paint, or an epoxy system, then you will want to make sure your garage floor is repaired properly to make it is as blemish-free as possible. Suppose you are covering your floor with a tile or mat flooring. In that case, repairs may not be necessary unless you are trying to stop a continuing problem like pitting and spalling or you are worried about water penetration.

Why do garage floors crack?

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Garage floors crack – period. Concrete is not a ductile material, meaning that it neither stretches nor bends without breaking. It does shrink and expand with temperature, however, and as a result, it cracks.

Most floors have contraction joints built into the slab that allows for this cracking. These are usually those deep grooves or saw cut joints that you see in the concrete that appear to divide a typical two-car garage into four separate slabs. These grooves create a weakened line in the concrete that encourages cracks to follow the groove instead of wandering across the surface.

As well as contraction joints work though, you still can get cracks in other parts of the concrete due to the settling of the earth underneath the slab, curing issues, or other variables beyond your control. The good news is that the majority of cracks are cosmetic and not structural. This means that they can be repaired to accept most any garage flooring.

Types Of Cracks In Concrete

Some cracks are more concerning than others. Here’s an overview of crack types and what to do about them.

  • Hairline cracks at the surface should be repaired if they are widening with time, are a hazard, collect dirt or are unsightly.
  • Shrinkage cracks occur while the concrete is curing and can be reduced or prevented with proper joint placement.
  • Settlement cracks happened when the ground beneath the slab wasn’t compacted properly and part of the concrete sinks.
  • Structural cracks wider than a credit card, or that run through the entire slab require repair or replacement of the concrete.

Acceptable Crack Widths

At what width does a crack in concrete become a problem? That question often arises, but unfortunately, there is no definite answer. It can vary from one project to the next. The answer may also change with the person’s perspective: What is acceptable to the contractor, engineer or architect may not be acceptable to the owner, who must live with the crack day after day. Even the American Concrete Institute has no standards or recommendations that give a “yes” or “no” answer as to what cracks need repair based on the width and other factors.

In general, cracks wider than a credit card and running through the depth of the concrete are structural and could be a sign of more serious problems (see Concrete Crack Repair Evaluation). These cracks — no matter what the width — are rarely acceptable. Consult an engineer or concrete repair professional to determine the cause of the crack and to recommend the best repair solution.

For hairline or non-structural cracks in concrete, the answer as to what’s acceptable is less clear. The width at which they became a problem requiring repair often depends on the following factors:

  • Is the crack static, or is it gradually becoming wider? If you notice the movement of the crack, it may continue to widen if the crack isn’t repaired and could indicate a structural problem.
  • If the crack is in a horizontal surface, such as a floor or slab, is it wide enough to present a tripping hazard?
  • In foundation walls or slabs, is the crack wide enough to allow moisture seepage?
  • Does the crack trap dirt and present a maintenance or sanitation issue?
  • Is the crack an eyesore and located in a high-visibility area?

Be aware that if you decide to repair the crack, the repair itself is likely to be visible unless you cover it with an overlay. However, it’s often possible to disguise or accentuate a crack through saw cutting, staining and other techniques.

Your Cracked Concrete Garage Floor Will Likely Get Worse

Don’t let anyone tell you that a small crack in any concrete slab isn’t a problem.

Sure, some surface cracks could be superficial and only affect the appearance of your garage. Even if that’s the case right now, the slab’s condition could easily worsen.

Any concrete damage, even small cracks, leaves the slab vulnerable to moisture penetration. If moisture penetrates the slab, the crack is likely to spread. Eventually, the structural integrity of your garage could be at risk.

If your concrete floor already has active cracks – which are typically caused by foundation settlement – structural damage may occur if you don’t have it repaired.

Cracked Concrete Repair Protects Your Home’s Value

You may not be planning to sell or refinance your house in the near future, but who knows what the future holds?

Having your cracked concrete repaired is an important investment, as it helps maintain the value of your home. When the time comes to sell or refinance, you naturally want the highest possible market value.

And, when you do finally sell your house, cracks in the concrete raise an ugly red flag to potential home buyers. In that case, you aren’t likely to command top dollar for your home, and you may have trouble attracting buyers at all.

How to Repair a Cracked Concrete Garage Floor

Superficial cracks can often be repaired with a bit of epoxy mortar. However, before deciding on this course of action, you should request an evaluation from an experienced concrete repair specialist. Surface cracks can mask a larger foundation settlement problem beneath the slab.

To be on the safe side, have your garage floor checked for underlying structural damage.

If you do have active cracking, joint sealer won’t solve the problem. Instead, mudjacking (concrete jacking) may be the best method of concrete repair for you. Mudjacking is quick and mess-free. And, even more important, this type of repair is very reasonably priced.

The average cost for concrete jacking is just $850. Larger jobs cost more, of course, but most homeowners pay between $500 and $1,207 for their mudjacking project.

If you wait too long to have your garage floor fixed, the damage could affect your home’s foundation. If you have severe foundation settlement, mudjacking won’t work to correct the problem. You’ll need to have pier supports installed instead. The average cost for structural concrete repair is a whopping $4,726.

Repairing Cracks In Your Garage Floor

The first thing you need to do when making a crack repair is to chase the crack. This is the process of using a hammer and cold chisel to break away any loose edges or material within the crack. The repair is only as strong as the material it adheres to.

If you don’t have a cold chisel, you can easily find them at your local home improvement centre or purchase them online from Amazon. We prefer the ones with the handguard.

Chase the crack by placing your cold chisel at an angle that runs in line with the crack. Firmly hit it with a large hammer or small handheld sledgehammer. The chisel will break away any loose material as you hit it with the hammer. Continue in this fashion until you have chased the entire crack.

Use a shop vac to clean out the loose debris and then scrub the crack well with a stiff wire brush. This will remove any weak laitance and prep the surface for the repair material. Vacuum out the crack again, and then you are ready to apply your repair.

Be sure to follow the directions carefully for the product that you use. If you use a 2-part epoxy gel or 2-part epoxy sand slurry, work it well into the crack in order to push out any trapped air. Once it’s worked in, trowel it as smooth as you can before the material begins to set up. Watch for any low spots that may need additional repair material added.

If you are using the Simpson Strong-Tie or similar product for larger cracks, it works best to fill 3/4 of the crack with silica sand first. Apply the Simpson Strong-Tie over the sand up to the top of the concrete. Allow a couple of minutes for it to soak in and then apply it again to fill in the low spots.

Once you do that, apply more sand loosely over the repair and let it sit for 20 minutes. After it has set, you can scrape off the top layer with a paint scraper or putty knife.

Once the repair has cured, you can grind it flush to create an even transition if you will be applying paint or an epoxy coating. This will prevent most repairs from telegraphing through the coating, and you will not see them.

Contrary to some information out there, you do not need to chisel cracks to form an inverted or backward-angled cut. This is only required of large repairs that are made using concrete or a cement-based patch.

Since new concrete does not adhere well to previously cured concrete, the backward-angled cut helps to keep the material from lifting out. Epoxy, polyurethane, and polyurea crack repair products, on the other hand, form a tenacious bond to properly prepared concrete and do not need an inverted cut to stay in place.

Another process which works well for chasing cracks is to use a small 4″ angle grinder with a crack chasing masonry wheel. The wheel is tapered to form a nice clean groove in the concrete.

When repairing deep cracks, it’s best to fill the crack part way with silica sand. This will prevent the repair material from seeping down deep into the concrete and settling. It saves you from using excess material as well as creating low spots that need to be refilled.

Low Spots And Other Repair Issues

One thing we did not cover is sunken slabs. Unfortunately, these are not a quick fix and can be costly to repair. These can be caused by severe settling of the soil, poorly reinforced slabs, or something worse, such as underground water problems. Sometimes the only alternative is to tear out the old slab, address any soil compaction requirements, and pour new concrete.

However, if you just have low spots in your slab that collect water due to a bad finishing job, there is an answer. You can use a self-levelling polymer-modified topping or epoxy slurry to fill in those low spots. Don’t fill in any of your contraction joints. If you do, you can scrape it out later as it starts to harden. Just make sure the product you use is designed for outdoor use.

Properly completed, repairs can last for years if not the lifetime of the garage floor. If you can patch a wall before painting, then you have the skills to do the same for your floor and avoid the much more expensive option of having someone do it for you.

Common Reasons There are Cracks in Your Garage Floor

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Shrinkage

Cracks related to shrinkage are typically nothing to worry about and are common. Natural shrinking occurs during the curing process, so it’s normal for even relatively new concrete to have a couple of cracks. 

Settlement

The soil under your home or building can move and sink over time, a process known as a settlement. A little bit of settlement is normal over the years, but it can put pressure on garage floors and result in cracks. Settlement cracks are generally more serious than shrinkage cracks. Ultimately, severity depends on crack width and if it continues to grow or not.

Advanced settlement cracks are open buckets waiting to collect water. Unfortunately, this collection of water leads to greater problems, including the potential for sections of your garage to sink below others. This greatly increases your risk of flooding.

Depending on the layout of your garage, different areas will undergo a lot more pressure due to the weight of vehicle tires. This can naturally cause cracks to form, and the settlement may occur in corners of the garage. 

Look out for wide cracks where one side is higher than the other, as this may indicate more serious settlement issues. The sooner you identify issues, the better, so have a professional out if you are concerned.

Bad Installation

Original construction could be to blame if you’re noticing a lot of cracks on your garage floor. It is possible that builders poured a thin slab, didn’t add rebar reinforcement when needed or created an insufficient gravel base. Some common mistakes include:

  • Improper base, disturbed or uneven soil
  • Too low mpa of concrete
  • Not enough gravel

If the garage slab is poured at the incorrect level, water has a chance to move from an attached garage into the home. Furthermore, the garage floor slab must be poured so that it gently slopes down and away from the house to promote drainage.

Flooding/Underground Water Source

Water can play a huge role in the formation of garage floor cracks, especially if the water is not draining away from your home as it should. The presence of heavy clay or other types of dense soils clings onto excess moisture. Water-heavy soil may freeze during the winter, causing the soil to expand and put considerable pressure against the garage slab. This can cause heaving and cracking.

It is very common to see cracks near the garage door, that’s because this area has the greatest exposure to cold and frost. Check the perimeter of your garage for areas where water could get in and make sure it is well-sealed. Exterior soil levels should measure around six-inches below where your garage floor starts.

It is common for garage floors to develop cracks, some of which appear right after the floor is poured (i.e. shrinkage cracks). Others appear over the first year or so from the house settling slightly.

Older homes and homes built on expansive soils tend to have more cracks, but even if they do, the question becomes if the cracks are significant or just normal for the age and geographic area.

Although there are many reasons for concrete slabs to crack, most do not lead to the serious foundation or structural issues; however, there are times that the cracks are a warning sign of foundational or other problems. In these cases, an owner or buyer should check a number of other things about the house in order to help determine the seriousness.

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