How to fix garage floor cracks

Do you have an unsightly crack that’s taking over your garage?  If you aren’t familiar with concrete repair, then you might think this to be the end of the world.  You imagine hundreds of dollars of repairs and fighting to get a professional in there to fix the damage.

Even for a homeowner with little experience in working with concrete repairs will be able to do this job because the skills required to repair cracks are only moderate in their complexity.

Concrete is a temperamental material, but under the right conditions, it can perform with durability and longevity.  There are a few varying factors that cause cracking in concrete like sideways expansion, lack of proper drainage conditions, extreme temperatures, or the settling and shifting of soil beneath the concrete.

The Right Conditions

The general rule for repairing a concrete crack on your own is that you can fix it yourself if the concrete is the same height surrounding both sides of the crack.  If the concrete is uneven on either side of the division, then it could be an indication of an underlying problem that could require an expert to analyze it.

Considering the underlying cause of the concrete crack will save you time, effort, and money in the future.  However, the causes behind a crack are not always obvious, but there are a few cases like the roots of a tree displacing the concrete, or the sure signs of standing water in the area of the crack that will certainly freeze and contribute to the concrete’s breakage.

You don’t want to be out in your garage a month or so later doing the same job once again.

Getting Started

Your first step will be cleaning the area in question before you make any actual repairs.  Sweep the garage to see the layout of the crack, and it is even advisable to get out your power-washer and hose off the area, squeegeeing away any excess moisture. You might want to have your shop vacuum nearby to clear away any of the smaller pieces of concrete later when you get to work on the crack.

Your garage floor may be stained with the typical substances common to spilling on garage floors like oil and grease.  If this is the case for your garage floor, especially near the area of the crack, then grab some Trisodium Phosphate (TSP), a product that can be purchased at your hardware store, to get out these tough stains.

This all may seem like extra work, but your concrete filler will be able to settle nicely with the removal of all contaminates. When it comes to concrete repair, it gets worse before it gets better.  In most situations, you’ll have to enlarge the crack before you fill it.

This will help you clear out the debris inside of the crack in order to put down fresh filler. Make sure you remove any big chunks of concrete that may have come loose or have broken off, and you should be sure to use a wire brush to sweep away any of the finer particles.

Is your cracked concrete on your garage floor deep and wide?  There’s no need to worry because you can actually fix deep and large cracks yourself, too, but it just may take a few extra tools to do the job.  For these types of cracks, use a circular saw fitted with a diamond blade.

Make deep grooves on each side of the crack so the filler can be easily added into the channel.  You will have to wear a respirator for safety and have a fan going to control the amount of dust in the garage, pushing it outside.  Use a maul and chisel to work our any other chipped or cracked pieces.

Filling in the Groove

Now that you have thoroughly cleaned and swept up the area free of any remaining debris, dirt, and grime, it’s time to put your concrete filler to work.  You should have a fresh surface for the filler to bond successfully.

At this point, you’ll want to buy concrete filler, and if you want your repair job to last, pick up some concrete sealing product as well.  Some people also buy a latex modifier to mix with their concrete filler and together, add both products into the crack.

For many concrete filler products, you’ll need to cut the application nozzle off of the bottle, then slowly and carefully fill the cracks.  Follow the instructions on the product’s label for proper application and mixing of your concrete filler.  Once you have poured some of the filler into the crack, wait a few minutes for the product to settle.  You might need to add more to ensure you are creating a tight seal.

Patience is key at this part of the process.  Whatever filler you are using, regardless of what the concrete product is mixed with, you are going to have to wait for it to cure for a few hours, preferably overnight.  Check the instructions on the labeling on your products for the appropriate dry time.

Applying a Sealant

Concrete is a known absorber of stains and will soak up anything that’s spilled on its surface.  Grease and oil are frequently used inside garages and you’ll want to use a concrete sealant to protect your new application from becoming stained by these stubborn substances.

You also don’t want your new repair to suffer a crack again, and by applying a sealant or resurfacing agent to the new filler can help protect it.  Your garage floor is being exposed to heavyweight from cars and equipment and also high foot traffic, and in combination with shifts in the temperatures can cause cracking.

A heavy-duty water-based polyurethane sealant should do the trick in situations such as these, and the best part is that this product dries quickly so you can add multiple coats for effectiveness. If your garage floor is rough, apply your sealant with a broom or anything with substantial bristles to really work the sealant into the surface’s grooves and pockets.

Then, smooth the sealant with a roller or a squeegee.  Your second coat of sealant, depending on what the instructions tell you, can probably be applied within a few hours.  If your crack is in an area that’s prone to a high volume of traffic, you might want to consider applying three or even four coats of sealant.

Repairing a Cracked Concrete Floor

Most of the times, those smaller cracks in your garage floor can be easily repaired.  For bigger cracks, yes, you can repair them, but you might want to do a little investigating as to why they occurred initially.  Ask yourself if your garage has any previous drainage problems and check into this issue after a good rainstorm.

If you have any concern about the underlying causes of your garage floor cracks, then you should consult a professional.  A consultation will be worth the small expense in order to solve the root issue of the cracking.  As for the actual repairs of the concrete cracks, it can be as easy as adding in a little concrete filler and applying some sealant.

At Danley’s, your new detached garage will be built from the ground up.  Our professionals handle concrete, construction, and electricity.  With plenty of styles and options to choose from, speak with a specialist and get a free quote today.  Since 1959, we’ve constructed over 100,000 detached garages and we’ve always delivered on quality no matter how big the project is.

Cracks in a concrete garage floor may indicate that there are foundation problems or other issues. As buyers or homeowners, we want to know how to tell if these cracks are serious, or 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.

Cold joints look like cracks but are OK

One of the most common mistakes that people make when looking at their garage floor is to confuse a cold joint with concrete that has actually cracked.

A cold joint is intentionally placed in concrete by the concrete contractor when pouring the concrete. Basically, a cold joint is where a section of concrete has been poured and then after it has hardened they pour another section of concrete next to it. Some people may confuse these joints with control joints.

Control joints and cracks

Many concrete contractors will say that there are two types of concrete. “Concrete that has cracked and concrete that is going to crack”. This saying has a lot of truth to it.

Since contractors and engineers know that most concrete is going to crack, they like to control where it is going to crack. They accomplish this by placing control joints in concrete slabs, often 10 to 20 feet apart and in both directions. These control joints are designed to weaken the concrete in certain areas so that the concrete will crack in a straight line in these spaces. They may be troweled into the concrete or thin plastic strips may be embedded in the fresh concrete to weaken it. A good example is a long sidewalk that has control joints about every 5 to 10 feet. Read more about concrete joints

With garage floors, contractors use mostly control joints and occasionally cold joints. Neither of these is inherently bad and are seldom a problem.

New Homes’ – Cracks that occur in the first few months or years

Shrinkage cracks

When a garage floor is first poured, the concrete begins to harden (contractors say cure) and when this process takes place the concrete shrinks a little; a 20 foot square of freshly poured concrete will shrink about a 1/8 of an inch in each direction. As this happens small shrinkage cracks appear in the concrete. These are normal and generally are not much of a concern.   Read more about concrete shrinkage cracks

Cracks from a new home settling

In the first year or two, it is not uncommon for a new homes’ foundation to settle a bit. As this settling takes place the slab will often develop a few cracks due to this settling, but in the overall picture, these likewise will normally not be of much concern.

Cracks during construction

Builders often say that “Time is money” and therefore push the contractors and sub-contractors to get their work done sooner.

In this haste, the framing contractor often wants to start framing the house as soon as the foundation and slab are poured. From a technical standpoint, the concrete needs some curing time before anything heavy can be placed on it; the concrete needs to achieve a certain strength before heavy lumber and equipment get onto the concrete. Depending on the type of concrete it usually takes 5 or 10 days and even up to 4 weeks before heavy equipment and loads can safely get onto a concrete slab; most concrete reaches full strength in approximately 28 days.

If a framing contractor drives a piece of heavy equipment loaded with lumber onto a 4 inch thick concrete slab, he may crack the green (not fully cured) concrete

Crazing cracks

Very thin hairline cracks in random or irregular hexagonal patterns that are very shallow, usually less than an 1/8 of an inch deep, are often called crazing cracks. They are caused by improper troweling and placement of the concrete; the thin top layer of concrete dries out faster than the rest of the concrete, thus these hairline cracks. They are generally of no concern when it comes to structural integrity. You are more apt to see these types of cracks on a garage floor that has a hard smooth troweled surface than one that has a broom finish.

Cracking due to poor compaction of sub-grade

Before pouring a concrete slab it is important to prepare what is often called the subgrade which usually involves compacting the subgrade and base (i.e. gravel and /or sand on top of the sub-grade). If these sub-layers are not well compacted then when concrete is poured on top of them, the heavyweight of the concrete will cause these areas to drop down a little, then cracking may occur.

Slab reinforcement: Rebar, Post tension cables, or Wire mesh

One of the most important aspects of a concrete slab is the steel reinforcement in the slab. It reduces cracking and makes the slab much stronger.

Rebar

Rebar steel reinforcement is probably the most common form of reinforcement used in concrete slabs for the last 40 to 50 years. This type of reinforcement is usually placed at 12, 16 or 24 inches on center in each direction of a garage slab. The majority of these slabs are about 4 inches thick, however, a few may be 5 or 6 inches thick.

If you see a cracking or rusting pattern in the garage floor that looks like the cracks are 12 to 24 inches apart running in one or two directions, it may be an indication that the rebar was placed a little too high and doesn’t have enough concrete to properly cover the rebar. Usually, these hairline cracks will run parallel to one another.   Read about rebar problems and warning signs of problematic rebar in concrete 

Post tension slabs

Post tension slabs have steel cables that run through them, similar to rebar but are further apart. After about seven days these cables are stretched tightly with hydraulic jacks which put the slab under compression and help spread the weight (load of the house) over a wider area than the footings alone. This type of reinforcement is becoming more popular and is now used more often in areas that have expansive soils. Read more about post tension slabs and why you should not cut or core one

If a garage has a post tension slab there is usually either a sign stamped in the concrete floor saying it is a Post Tension slab or a plastic sign on the garage wall stating it’s a Post Tension slab. Remember that you should not saw cut the slab or core holes in it for safety reasons.

Wire mesh

There are a number of garage floors that have welded wire mesh reinforcement in them. The wire mesh usually comes in rolls or sheets and is placed in the concrete slab, approximately in the center of the slab; in a 4 inch thick slab it would be about 2 inches from the top and 2 inches from the bottom or the slab. In some cases this wire mesh does not end up in the center area but lays on the subgrade with concrete just poured over it, thus it doesn’t perform as well as it is designed to.

A concrete slab without reinforcement will crack substantially more than a reinforced slab and is weaker.

A concrete slab without reinforcement usually will have more cracks and the cracks will be wider than cracks in a reinforced slab. Nearly all newer homes will have reinforced slabs, however older homes, especially those built in the early sixties or before may not have reinforcement or very little.

Photo on left is an extreme example of a concrete slab without steel reinforcement. Keep in mind a slab without steel reinforcement usually does not look as bad as the photo but is more prone to cracking, than a slab without reinforcement.

Tip. If a concrete slab has a crack where one side of the crack is an 1/8, 1/4, or 1/2 inch higher than the other side, then there is a pretty good chance that there is no rebar or other reinforcement in the slab; for if there was reinforcement, both side would be roughly level, not offset.

Structural concerns

When a garage floor has a significant number of cracks or that they’re wide cracks or when a crack has one side substantially higher than the other side; then examining these cracks further and checking the home for other signs of possible soil and foundation movement would be wise.

Look at more than just the cracks

In order to help analyze if the cracks are a concern, you must look at other factors in the home. If you see some of the following, then the cracks may relate to foundational or other issues.

• Are the floors of the house sloping? Un-level floors are a sign of structural movement.
• Are there doors or windows that are inoperative or difficult to open or shut?
• Is the foundation cracked, leaning or bowed?
• Does the roof sag?
• Are there cracks in the drywall or siding?
• Does a crack across the garage floor continue up the garage wall?

When there are other issues like those above with a house, then garage floor cracks become more of a concern, for they are then part of the overall picture of the home and may relate to foundation issues.

Note. If a home is on a hillside lot and there is a living area or an open space area underneath the concrete garage floor, then all cracks should be evaluated for safety purposes. Should the cracks have rust stains, run extended lengths, be more than hairline cracks or getting worse; consulting a structural engineer would be wise.

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Bottom Line

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 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.

After you have fixed all of the cracks in the concrete, consider adding an epoxy coating to the garage floor.