While you can't avoid every concrete crack, you can help keep most at bay
Concrete might be one of the most durable building materials around, but it's tricky to lay. No matter how good a job you do, eventually, cracks are inevitable. But if you want to prevent them from forming straight away, ensure the best longevity, and prevent costly repairs, follow these five simple tips for a crack-free finish in your patio or driveway.
1. Don’t Go Overboard With Water
Concrete is notoriously tricky to mix, and it’s tempting for many novice DIYers to add a bit of extra water to make the job easier. But not so fast—even a small portion of water over the recommended amount can weaken the concrete. The excess water evaporates, leading to shrinkage once the mix is laid and, eventually, cracks.
Make sure you select the correct type of concrete mix for the job and follow the instructions carefully. If you need a little extra water to remove any dry bits, add it very sparingly.
2. Cure Your Concrete Carefully
Though concrete takes almost a month to cure completely, the curing process is most sensitive during the first few days after pouring. What you do during this window impacts whether you end up with shrinkage cracks.
Although the cracks that form, often referred to as map cracks, are typically only cosmetic, it doesn’t make for an attractive finish. Sometimes severe cracking can also occur, impacting the overall strength and integrity of the finish. So after pouring, keep your concrete moist and free from load-bearing.
Keep the Concrete Moist
You want the moisture to evaporate from the poured mixture gradually. There are a few things you can do to help it cure:
Spray the concrete with water a few times a day for a week after curing. You might need to do this more frequently during hot weather.
Lay a wet, moisture-retaining fabric on top of the curing concrete. Just make sure the concrete’s surface is hard enough that the fabric’s weight won’t cause any damage.
Purchase a curing compound. You can spray this onto the concrete immediately after laying it to form a protective layer that retains moisture.
Keep an Eye on the Weather
The best time to pour concrete is during warm weather. Don’t attempt this job when surface temperatures could drop below 35 degrees Fahrenheit. If there are any unexpected temperature drops (below 50 F) the week after laying, cover the concrete. Using an insulated or heated blanket or thick polythene sheeting helps prevent structural weakness and cracking.
You’ll also want to shelter your curing concrete from strong winds, which can also cause surface cracks.
3. Use Control Joints
Concrete will inevitably crack at some point, but inserting control joints keeps them from randomly appearing. Instead, you’ll be able to direct cracks to spots that are easier to repair with a concrete sealant.
Add the control joints within 24 hours after pouring. You can use a few different types: they can be hand-tooled using malleable concrete, created by placing flexible wood fiber or plastic strips, or you can wait until you can saw the concrete to create them.
The correct placement of these control joints is vital; otherwise, they won’t do the job they are supposed to. Typical 4-inch deep concrete should have control joints placed no further than 8 to 12 feet apart.
4. Prepare the Base
A well-prepared base decreases the chances of premature settlement cracks. The sub-grade should be smooth, well tamped down, have good drainage, and be frost-free. Without this sturdy, stable base, the concrete slabs will have more room for movement, and cracks will form.
Loose soil is an absolute no-no, so don’t dig too far down when preparing your sub-grade. This could result in having to refill some of the space with more soil, leading to more settlement issues.
5. Add Reinforcements
To give your concrete extra strength, consider adding some extra reinforcement underneath. Steel rebar or, for smaller projects, wire mesh grids can help extend the concrete’s life span and reduce the number of future cracks.
When to be Worried About Concrete Cracks
Most hairline cracks are more of a cosmetic problem. Though they look unsightly, any crack that’s one-eighth of an inch or smaller is considered standard.
If a deep crack forms that’s wider than a credit card, this could signify a more serious issue. On the ground, it’s a trip hazard, and foundation cracks can cause structural problems. If you have concerns, you can have a local contractor assess the damage and recommend a repair solution.