How to Fix Cracks in a Concrete Patio

Concrete is tough, there’s no question about it. And yet, under certain conditions, it can develop cracks which, aside from an eyesore, can be quite the tripping hazard! No need to worry though—except in more severe cases, you can fix cracks in a concrete patio with the right equipment and a little know-how. Ready to know more?

How Does Concrete Get Cracks?

If it is so strong, so resilient, why does concrete even crack? If it was laid down recently, the possible causes (too much water in the mix, concrete drying too fast, among others) can be best averted before they happen, by hiring a reputable contractor that will do the job right.

It may be more expensive than tapping a cheaper person for the job, but it will pay for itself with the headaches it will save you down the road.

If, on the other hand, the concrete has been there a while, the main factor often has to do with the ground underneath: if it shifts due to moisture variations, or it is not strong enough for the weight, you will notice the floor at the top cracking. This can also happen if there are rodents tunneling underground, eroding the soil and leading to the same outcome on the concrete.

Furthermore, if your patio happens to freeze and thaw repeatedly during a particularly harsh winter, this can cause cracks to appear (or grow in size) regardless of how weak or strong the ground beneath is.

Can You Fix Cracked Concrete?

Maybe, maybe not. This list is a good reference point to determine if you can tackle the job yourself, or if you need to get a professional involved.

• Area size. If the cracks are all over the place, resurfacing might be a better idea—as long as said cracks are not too deep.
• Movement or tilting. If you notice the cracks are shifting, then the ground beneath might be unstable; tilted concrete is also best left to a professional.
• Rust. If it is coming out of the cracks, then the rebar reinforcement is likely corroded, which can eventually lead to spalling, i.e. chunks of concrete coming off. This will take more than a mere patching job to resolve.
• Delamination. This happens when the concrete begins flaking off, and it can compromise the concrete’s structural integrity if it is severe enough. Though it can often be detected visually (by the loss of flakes on the surface), it is not rare for it to occur too deep for you to catch it at a glance. In this case, a sound test can help: tap the area with a hammer, and if it returns a hollow sound instead of a clear ringing noise, then there is delamination that needs addressing, and which won’t be so easily patched, as it has to do with how specific steps are performed when the concrete is laid down.

How to Assess the Damage

The tasks we’ve outlined are easy enough, but it’s perfectly okay if you don’t trust yourself to make the decision between repairing this damage on your own or bringing in a contractor.

There are certain tests that can be performed, and which will yield a wealth of information on your concrete’s quality and status, without even scratching the surface. Since they do not require any damage to the concrete, they are known as non-destructive evaluation, or NDE; Impact-Echo is a common example.

Depending on the NDE’s results—or if one cannot be conducted—, it is always possible to perform a more intrusive test, such as drilling out a portion of concrete and sending it to a petrographer, who can give you a comprehensive diagnostic following an analysis of the sample under the microscope.

Do I Need Permission to Fix Concrete on my Property?

Generally, no—as long as it doesn’t go beyond patching up a few cracks. More complex jobs for repairing the concrete (or replacing it, in some special cases) will likely require a permit. It never hurts to contact your local permit office… and your HOA, while we’re at it.

What’s the Best Weather for Concrete Repair?

Whichever material you use for repairing the crack (which we will cover more in depth soon) will need to dry, and any moisture (present or imminent) could severely compromise your efforts. For your patching job, make sure the concrete is completely dry—don’t let anybody run a mop on it, for example.

Ambient temperature should range between 50 and 90°F, and no rain should be expected for at least 24 hours after your job is done, unless your patio is fully covered and no rainwater can get to it; if this is your case, then it should be fine to proceed with the repair even if it’s raining.

Pour it into the crack, smooth it out with a putty knife, and let it dry. The right product will go as far as filling up cracks as wide as 1 inch, and will not require using the putty knife; it is, indeed, fairly runny, which makes it great for your patio—but not as optimal for your walls!

How to Repair Large Cracks in Concrete

Is it 1 inch wide, and deeper than ¼ inch? Then the procedure will be a bit more labor intensive, and will require more tools.

What You Will Need

Let’s start with the shopping list.

• A set of safety glasses, and appropriate hearing protection. For the latter, you can get extra fancy and go for something that will even allow you to talk on the phone while you work.
• A wire brush, and a shop vacuum.
• A sledgehammer and a heavy-duty flat chisel.
• A trowel.
• Patching compound. Many of them are concrete-based and require mixing prior to application, but there are some exceptions.
• If the crack is over ¼ inch deep: a few fistfuls of clean sand, and a funnel. Alternatively, you can procure some closed-cell backer rod, and a utility knife.

How to Get It Done

Tools at the ready? Then let’s hop to it!

1. For starters, we must widen the crack. Put on your safety glasses and hearing protector, lean the chisel into the crack at a 45° angle, and give it a light tap with the hammer. Move the chisel a little to the side, and tap it again. The idea is to create a V shape, which is better for the patching compound to settle into. Be mindful not to chip away larger chunks of concrete; try to keep the width at about twice the crack’s depth.
2. Next step is cleaning the crack. Get in there with your wire brush, and sweep up every bit of debris and dust you can. When the brush has done its part, use the shop vacuum to scoop up anything left.
3. For the compound to work properly, the crack should be at a depth of ¼ inch. Inspect it, and fill any deeper sections with sand until they are at appropriate level. Hold a fistful of sand in one hand, the funnel with the other, and pour gently where it is needed. As mentioned, you can use backer rod instead of sand, but you have to make sure it is really lodged in there. Lay it down where it is needed (i.e. anywhere deeper than ¼ inch), cut it to appropriate length with the utility knife, push it in with your fingers, and then use something flat and blunt to firmly shove it in place. Don’t use a screwdriver or anything sharp, as they could puncture or slice the rod. Once it is all the way in, you can proceed to the next step.
4. Patching time! Whichever product you choose, remember to refer to the manufacturer’s instructions: some products might require shaking, for example, or successive applications in very thin layers. Tamp it down as you go, to eliminate any air pockets. Once it’s all packed into the crack, flatten it with the trowel or a putty knife.
5. You’re done! All that’s left is allowing the patch to cure; manufacturer’s instructions will usually disclose how long this can take, depending on the product used.

Helping It Last Longer

Your repairs are done; here’s what you can do so you won’t have to repeat the job too soon.

• As frigid temperatures come and go, water can seep into the cracks and then expand as it freezes, exacerbating the damage. For this reason, if you see cracks and winter is upon you, try to get them repaired as soon as you can. Same if you see flakes coming off the top: this will leave a more porous surface exposed, making it that much easier for moisture to seep in and potentially cause damage.
• If you must use an ice melt, be mindful what you pick. If at all possible, pick something formulated with magnesium chloride, which is widely considered to be less corrosive. Calcium chloride might be your best bet if your temperatures consistently drop below zero (which is where its magnesium counterpart is almost completely ineffective), in which case it would be wise to make judicious use of it.
• If you need something to shovel snow, try to avoid metal unless the loads you have to deal with are particularly heavy.
• If at all possible, consider providing your patio with some cover; even a canopy will help. The more moisture you prevent from getting into contact with your concrete, the better.
• Bringing in a fire pit? Then add adequate shielding; the extreme temperatures at the fire pit’s bottom while in use can damage the concrete, especially if both come into direct contact. Even better: raise the fire pit on top of some bricks or pavers.

In Summary

Cracks on your concrete floor don’t have to be the end of the world; in most cases, you can tackle it yourself without too much trouble. Just remember your due diligence: if those cracks are too widespread, deep or lopsided, there’s nothing wrong with leaving the job to a qualified professional. And once the job’s done, a little bit of care will help ensure you don’t have to worry about it again, for quite a while!