Cracks in a concrete garage floor may indicate that there are foundation problems or other issues. As buyers or owners, we won’t 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.

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WHY 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 in nature. This means that they can be repaired to accept most any garage flooring.

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Common Reasons There are Cracks in Your Garage Floor

The good news is that there are only a few things that can go wrong with a concrete floor. Most of them are simple to fix. By simple, I mean they don’t require any major expertise or specialty tools. They do require some elbow grease though. As with many things of this nature, it is the prep work that makes the difference. Power tools do help with larger surface repairs.

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.

Here’s a look at some of the most common reasons for cracks in garage floors.

Expansion

Concrete tolerates heavy loads, but it has low tensile strength. In other words, it does not bend or stretch well. Extreme temperature fluctuations could result in cracking.

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.

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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.

How to Diagnose a Dangerous Garage Floor Problem

Far be it for me to tell you what you can and can’t do, but here are my two cents. Garage floor Excessive damage and deep structural issues require professional help. Here are some signs that the problem is more than skin deep:

  • cracks where one side is higher than the other
  • cracks or crumbling in low spots
  • a constantly wet garage floor
  • a persistent puddle in one area of the garage
  • 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? (See Foundation and Basement Crack Repair.)
  • Does the crack trap dirt and present a maintenance or sanitation issue?
  • Is the crack an eyesore and located in a high-visibility area?

If your garage floor shows any of these symptoms, then there might be a serious underlying problem. There might be a large accumulation of water attacking the floor from underneath. If your garage floor has a water problem, it will soon have a structural problem, too. Ask a concrete professional to diagnose the problem, and to suggest repair solutions. Any surface fix applied to a bigger problem will soon wear away. Water can crack concrete into pieces. No amount of do-it-yourself mortar or epoxy will stop that process.

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.

Cracks are repaired on a garage floor 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.

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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.

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RECOMMENDED CRACK REPAIR PRODUCTS

Always use an epoxy, polyurethane, or polyurea based crack repair or crack filling sandable compound. These cures and harden at a strength greater than concrete and will prevent water intrusion as well. You can grind or sand them flush with the concrete, and they will accept paint or an epoxy coating.

Do not use inexpensive water-based or latex-based concrete crack filler and repair products. This is what most home improvement centres carry since they are cheap and easy to use. The problem with them is that they are not sandable, they will not accept paint, and they will shrink over time and pull away from the repair. Do not use a self-levelling sealant either as these are designed mostly for sealing control joints in the concrete.

One such example of an epoxy-based crack repair product that we know works very well is Simpson Strong-Tie Crack-Pak at Amazon. It comes in a 9 oz. a cartridge that requires a caulking gun to apply it. The 2-part epoxy is separated inside the container. The self-mixing cartridge tip eliminates the need to mix the 2-parts together and makes application easy.

Because it flows very easily, it’s a great choice for repairing garage floor cracks less than 1/8″ wide. For deep cracks or cracks larger than 1/8″ wide, you will want to partially fill the crack with clean play sand or silica sand first when using this product. This will slow the flow of epoxy from going deep into the crack and using more than necessary.

Another excellent crack repair product that we have experience with is PC-Concrete Epoxy Crack Repair at Amazon. It is a thicker flowing epoxy that requires using a putty knife to work into the crack. It also works well for filling small holes and divots in the concrete. Like other cartridge epoxy repair products, it comes with a self-mixing tip as well.

What we like about PC-Concrete is that it fully cures in only 4 hours. This means that you can repair your cracks and grind them flush the same day.

A third product that we can recommend is Rust-Oleum’s EpoxyShield Concrete Patch. This is a 2-part epoxy as well that requires you to mix the separate Part-A and Part-B materials together on a piece of cardboard or wood.

When mixing the two components together, be careful not to mix too much at any one time. The epoxy does set fairly quickly, and you will only have a short time to use it. If your repairs are not all ready to be filled, you will run out of working time, and the epoxy will become too thick to use.

You can sometimes find it at most home improvement centres, or you can purchase it here at Amazon.

If you are repairing numerous cracks larger than 1/4″ wide, then your best bet would be an epoxy concrete patch kit that is available in 1-gallon containers or larger. This type of product is an excellent choice for deeper and larger width cracks that span a long length of the garage floor.

These usually consist of a 100% solids epoxy gel that has a sand aggregate that you can mix in as a filler. Once you apply it to the crack, it can be troweled smooth with a concrete float. One of the favourites that we recently reviewed is Xtreme Set 100 by Legacy Industrial.

You will not find a product like this at a home improvement centre either. Instead, they are much more common in the professional floor coating industry and will need to be purchased online in most cases. You can find a good example of such kits anywhere.

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Will the cracks return through the coatings?

Unfortunately, the answer is “maybe”. Since the return of the original crack or formation of new cracks that show through the coating depends upon many factors (such as slab vibration, slab expansion & contraction, hydrostatic vapour pressure), there are no guarantees regarding cracking. Anyone who guarantees a concrete slab will never crack or that the crack will never telegraph through the coating is making a foolish statement.

Plus, using a coating such as a decorative chip decreases the likelihood that a very small, tight crack would even be easily visible in the coatings. 

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 a 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 to help determine the seriousness.

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