You take great pride in your concrete driveway and walkway. That’s why it’s especially upsetting to see cracks in your concrete when you’ve tried to remain meticulous about upkeep. What has happened here and what should you do about it? How do you prevent cracks in concrete?
To keep concrete from cracking, try these suggestions:
- Ensure the base is compacted
- Use only the recommended amount of water when mixing concrete
- Always add control joints
- Let your concrete fully cure
In this post, we’ll discuss the types of concrete cracks and delve deeper into the above methods for preventing future cracks. Whether your walkway is a few years old or you just got it redone several months ago, you’re not going to want to miss this!
The Types of Concrete Cracks
Concrete doesn’t always crack the same. Depending on what has caused the crack to occur, you could have a very minor one or a crack that looks more like a gaping chasm. Here are four types of concrete cracks to be aware of.
Structural Cracks
If the name structural crack sounds serious, that’s because it is. These cracks are quite wide, greater than the width of a credit card. More so than that, they’re extensive, often encompassing a whole concrete slab or several.
When dealing with a structural crack, you have two options. You can either commit to extensive repairs or replace the slab altogether.
Settlement Cracks
We’ll talk a little later about compacting the base, but it’s an important step when pouring your own concrete. If you make a mistake during compacting, then the concrete will sink lower than it should. This is how you end up with settlement cracks. We’ve all walked over settlement cracked concrete before, and it’s jarring as one slab is lower than the others.
Shrinkage Cracks
You’ll also learn more about joints and curing later, which are two crucial elements in pouring concrete. When done right, you can prevent shrinkage cracks. These cracks occur due to misaligned joints or lack of curing.
Hairline Cracks
The last type of concrete crack is a hairline crack. These are the smallest and thinnest cracks of all, typically thinner than your credit card. At the time they happen, they likely necessitate no repairs. Keep an eye on hairline cracks though, as they can become wider as time goes on. By that point, you will have to fix them. That’s also true if the cracks are a tripping hazard.
How to Prevent Cracks in Concrete
If you’re more than ready to learn about compacting bases, using control joints, and concrete curing, it’s time. Let’s talk about what causes cracks in concrete and how you can prevent them going forward.
Compact Your Base
If you’re laying down concrete at home, then your base must be adequately compacted. What does this mean?
Before you pour a drop of concrete, you need a suitable base first. You can compact native soil or use what’s known as base material. Designed for compaction, base material is solid and strong. It should be comprised of particles and pieces, but none that are so fine that they exceed 200 sieve.
Once you buy your base material, you need to ensure you have enough for your concrete project. If you’re pouring concrete for a driveway, for instance, you’d need a base of at least 6 inches. For a walkway, only 4 inches is required.
Then you’d use a machine called a base paver. The paver includes a plate that sits low on the machine and generates vibrations. As this happens, all the soil’s small particles become settled into the base material. Your base is then compacted.
Failing to adequately compact your concrete base leaves room for a void to appear between the materials. This can crack the concrete, as can the settling that’s more likely to occur. Make sure you’re also excavating the nearby ground when compacting the base. This too can prevent cracks.
How much soil do you want to dig up during excavation? Only as much as allows for a bit of gravel, such as a couple of inches, and the concrete’s projected depth. Make sure you’re precise in your digging, as digging too much and then replacing the soil will accelerate settling.
Don’t Overdo It on the Water
If this is the first time you’re mixing concrete from a powder, it’s easy to make mistakes. Pouring in more water than required though is a fatal error, as the resulting concrete is weaker than if you used the recommended amount of water. Just how much weaker? You can reduce the concrete’s strength by an astonishing 40 percent by adding in one extra quart of water according to Bob Vila.
If you have regular concrete, a ratio of 0.45 to 0.60 is ideal, with the 0.45 the quantity of water and the 0.60 the quantity of concrete. The stronger your concrete, the lower your ratio should be, so keep that in mind.
We always suggest following the manufacturer’s instructions when mixing concrete, as water-to-concrete ratios can vary. Let’s say you’re using Quikrete, a pretty renowned brand for DIY concrete pourers. If you have 80 pounds of the stuff, you need far less water, only 3 quarts, give or take.
You want a concrete mix consistency that’s wet but not soaking through, almost like oatmeal. If your concrete is a straight-up liquid, you added too much water. This doesn’t necessarily mean you have to start over though. You can always pour in a bit of dry concrete to even things out.
What if you go too far in the opposite direction and your concrete mix is very dry? If the mix is crumbling on you, that’s a problem. Pour in a spritz of water, then add more if needed until you get the desired consistency.
Use Control Joints
Concrete is not impervious to temperature changes. As the temps climb sky-high or dip way low, the moisture in the concrete from the water can vanish. This causes shrinkage cracks. Well, unless you’re using control joints, that is.
Control joints, also known as contraction joints, are strategically-installed joints placed in the slabs to ward off shrinkage cracks. Each control joint should go a quarter of the way deep into the concrete slab for crack mitigation.
Now, control joints aren’t necessarily a cure-all. The concrete can still crack. The joints prevent shrinkage but increase tensile strength within the concrete. Concrete’s tensile strength starts pretty low, between 8 and 12 percent compared to its compressive strength according to Cement.org.
The boost in tensile strength can crack the concrete, but underneath the surface where you can’t see it. This gives the concrete a fresher appearance longer and still makes the slab safe to walk across, as it’s not a tripping hazard.
You can add your control joints as you’re pouring the concrete. You can also use a concrete grooving tool to install your control joints after you’re done pouring. Concrete doesn’t necessarily harden right away, and until it cures, it’s malleable enough that you can fit the joints in.
Even if you forget to add your control joints until the day after you poured the concrete, that’s okay too. If you have a circle saw outfitted with its own concrete blade, you can slice into the concrete and install the joints.
Let the Concrete Fully Cure
The last method for preventing concrete cracks is to allow time for the concrete to cure. Curing, by the way, is not the same as drying. Your concrete should be dry in about a day or two, but as for how long it takes the concrete to cure? That’s more like 28 days.
When concrete cures, you’re allowing it to reach its ideal temperature and moisture level so the concrete can dry hard and be secure enough to walk upon. The concrete is at this point considered to have reached its max strength potential.
Okay, so you should wait 28 days before you use the concrete so curing can finish. Is there anything else you can do besides be patient? Absolutely. To prevent quick losses of moisture through evaporation, you can mist the curing concrete slabs with water. Do this a few times every day for the first 7 days post-pouring.
If it’s summertime or you live in a hot, humid environment, increase how often you spritz the slabs. In the wintertime or in any weather that’s under 50 degrees Fahrenheit, you should use polyethylene sheeting or a concrete insulating blanket on your new slabs. This will prevent the temperature of the curing concrete from dropping so low that it could crack.
Keep the sheeting or blanket on until warmer days are ahead, then you can resume misting the concrete with water.
Final Thoughts
Cracks in your concrete are more than just unappealing, but they can be possible tripping hazards as well. Whether you have minor hairline cracks or significant settlement cracks, now you know several great methods that can prevent cracks before they ever have a chance to develop. Best of luck with your concrete project!