If you’re laying down a slab of concrete, then you may wonder how long it will take to cure.
Most homeowners want the process to be completed as quickly as possible.
However, that isn’t always the best thing for concrete.
We have found out how long it takes for a concrete slab to cure and the processes involved.
How Long Does A Concrete Slab Take To Cure?
It takes 24 to 48 hours for the concrete slab to cure enough to walk and drive on it.
If you intend to drive heavy machinery on it, then you need to wait longer.
Heavy machinery can drive on a cement slab after 28 days of curing.
This is the amount of time it takes for a concrete slab to reach its full strength.
What Happens During The Curing Process For A Concrete Slab?
Many people make the mistake of thinking that curing is the same thing as drying.
That isn’t the case when it comes to concrete curing.
Concrete curing refers to the process in which water adds to the concrete mixture.
Over time, water or moisture continues to add to the concrete to keep it hydrated.
The longer it stays hydrated, the stronger the concrete becomes.
Curing is the process of hardening the concrete to its full strength.
To reach its full strength, concrete needs moisture.
A study done by the Cement Concrete & Aggregate Australia company showed that concrete that had moisture added to it for 180 days had 100% compressive strength.
That strength decreased according to how long the concrete had water exposure.
Concrete that dried immediately after installation only had 40% compressive strength.
This is, unfortunately, the type of curing, or lack of curing, that many homeowners perform when they’re concreting their driveways.
Their goal is to have their driveway hard enough to drive on as soon as possible.
The problem is that letting it dry immediately reduces the concrete’s strength.
Cracks form sooner.
The concrete degrades earlier.
They’ll need to repair it sooner than if they had allowed it to cure properly.
The study also shows how strong the concrete was after the standard 28 days of curing.
That sample shows that concrete has 95% compressive strength after curing for 28 days.
You may wonder why this is the case.
It all has to do with the interaction between water and concrete.
During the curing process, concrete molecules interact with water as it evaporates.
The longer and more often that the molecules can interact with the water, the stronger the molecules become.
Once water completely evaporates, then there’s nothing for the concrete molecules to interact with.
Instead, it dries and hardens as it is.
The curing process involves the addition of water or moisture to the concrete over a specific amount of time.
It continues to rehydrate the concrete to give the molecules a chance to interact with more evaporating water.
What Are the Best Ways to Cure Concrete?
Besides extending the time it takes to cure concrete, there are a few methods you can use to hydrate your concrete.
Professionals utilize these methods when curing concrete for businesses and public works.
The curing process of immersion involves submerging concrete completely in water.
This isn’t a process that many professionals use in the field.
Instead, it’s used in labs to test certain concrete specimens.
It helps to determine how certain new samples of concrete react with water.
If you’re planning on curing a concrete slab at home, then this method isn’t for you.
This is the most common type of curing process used in the field.
It’s only used if there are plenty of sources of water nearby.
Pooling involves adding a layer of water over the surface of the concrete.
It can only be used for flat concrete slabs and not vertical ones.
To keep the moisture in the concrete and ensure the water doesn’t leak out, sand and earth dikes form the sides of the slab.
The layer of water on top of the concrete is effective at keeping the moisture in the concrete.
There’s always some water for the concrete molecules to interact with.
When the layer of water starts to diminish, then the professionals pour or spray more water on top of it to replenish it.
It’s an easy way to check the moisture of the concrete without needing to touch it.
It also guarantees excellent curing.
The concrete has plenty of water to interact with and harden as a result.
This method is ideal for homeowners that have plenty of access to water.
You only need to pour enough water on the concrete slab until you see a thin layer of water on its surface.
Then continue to add water as the layer diminishes.
In places where there isn’t much access to water or there’s a restriction on the amount that can be used, fogging is another excellent process.
Fogging, or misting, refers to the process in which a sprinkler or similar tool sprays water vapor over the cement.
This thin amount of water is enough to keep the concrete moist.
It allows the concrete molecules to interact with the water and harden over time.
Since you only add a little bit of water over time, it cuts down on the amount of water that’s wasted.
This method is ideal for homeowners who don’t want to waste a lot of water or are unable to do so.
It will introduce enough water to your concrete to make it cure into a strong slab.
4. Wet Covering
The final process you can use to cure concrete is with a wet covering.
Professionals will use this method when there’s no access to water.
They’ll allow the concrete to harden to a certain point, and then they’ll place a covering over it.
The covering is wet with water.
It’s often made out of sand, straw, burlap, or canvas that’s soaked with water.
The covering presses into the concrete and keeps it moist over a period of hours.
Over time, the covering will dry out.
At that point, if enough time has passed, then the concrete is ready for use.
If it still needs time to cure, then they use another wet covering to continue its moisture.
This method is great for homeowners who don’t want to use a lot of water.
It also helps those who do want to use water but can’t watch their concrete for so many hours.
Applying the covering can allow your concrete to have moisture while you’re sleeping or away at work.
When you return, you can either change the covering with a fresh one or use one of the previous curing processes.
All of these methods require water to keep the concrete moist, but there are a few processes that don’t use water.
How To Cure Concrete Without Water
There are two main methods that you can use to cure concrete without using water.
These methods replace spraying or hosing down the concrete with water.
1. Plastic Sheeting
You’ll need to work fast if you want to use plastic sheeting to cure your concrete.
You also need to use the right kind of plastic sheeting.
The sheeting needs to be no less than 0.01 mm thick.
It also needs to cover the slab by twice its thickness if the slab is lying flat on the ground.
As an example, if the concrete slab has a thickness of two inches, then the plastic sheeting needs to be at least four inches wider and taller than the slab as a whole.
This is because a plastic sheet’s job is to block the sun from evaporating the water within the concrete slab.
Without the sheeting extending past the concrete, then the sun can leech past it and allow the moisture to evaporate.
The plastic sheeting needs to cover the concrete slab as soon as it’s set.
However, it can’t be so quick that it ruins the concrete’s finish.
Enough time needs to pass that the very surface of the slab hardens.
As soon as its surface is hard, the plastic sheeting needs to cover it.
With the sheeting covering the concrete, the moisture can linger inside the concrete slab longer.
While some evaporation is inevitable, it reduces the amount of time it takes to evaporate all the water from the concrete.
As a result, the concrete will grow harder and have more compressive strength.
2. Membrane-Forming Curing Compounds
The other method to cure concrete without water is to use membrane-forming curing compounds.
This is a specific type of chemical that sprays across the concrete once it’s laid down.
The chemicals create a protective layer over the concrete.
It reduces water evaporation and keeps the concrete moist for a longer period of time.
The layer, or membrane, is impenetrable.
This method is more expensive than plastic sheeting as it requires the use of professional-grade chemicals.
Homeowners may want to use plastic sheeting instead of dealing with chemicals.
What Factors Influence Cement Curing?
There are a few factors that can influence how quickly or slowly concrete dries.
Understanding these factors can help you better understand the environment the drying concrete is in.
With that understanding, you can make decisions that will help increase or decrease your curing time.
Humid days can affect the curing process of a concrete slab.
When a day is humid, it means there’s a lot of moisture in the air.
That also means it’s easier for concrete to cure.
The moisture in the air added with your own curing method can allow your concrete to cure for a long time.
You may not even need to use that much additional water to keep the concrete moist.
The opposite is true if there’s no humidity.
On especially dry days, the sun may be so strong that it’s sucking the water from the air.
On these days, you may need to use more water to keep your concrete moist and curing.
You can prepare for the amount of water you’ll need to use by looking at the weather report.
If you want your concrete to be as strong as possible, then you’ll want to lay it out on humid days.
If you prefer to have your concrete dry as fast as possible, then you’ll want to lay it out on dry days.
The temperature also plays an integral role in how well the concrete slab cures.
Hotter days are difficult.
They often mean that the sun is more powerful and is able to evaporate water faster.
You’ll use more water to keep your concrete wet during hot temperatures.
Mildly warm temperatures are the best.
A temperature of 50 degrees Fahrenheit is ideal for curing concrete.
It’s warm enough that the water doesn’t freeze, but it isn’t so hot that the water quickly evaporates either.
Cold temperatures can make curing difficult.
Temperatures that drop below 40 degrees and stay there can ruin your concrete.
Below freezing temperatures cause the water particles in the concrete to become solid.
In their solid form, they can keep concrete from hardening and can even cause premature cracking.
You may need to redo your concrete if the temperature drops into the freezing range.
Your concrete may be salvageable if the temperature climbs up past 40 degrees and goes above 50 degrees.
It needs to do so within 12 hours or else the water particles will ruin your concrete.
3. Initial Water Amount
To create concrete, water is added to the mixture.
It’s then laid out in the frame.
Inexperience may cause a problem.
If too little water was in the concrete mixture to begin with, then it started to dry prematurely.
You’ll need to add more water quickly to keep it from drying out and hardening.
If you don’t, then you’ll have weak concrete that is prone to cracking.
4. Accelerating Chemicals
You may find yourself in a situation where you need the concrete to dry immediately.
You can use certain accelerants to the concrete to speed up the drying process.
It works by dehydrating the water in the concrete and making it evaporate faster.
The problem with using accelerants is that you sacrifice quality for speed.
The concrete won’t be able to reach its full compressive strength.
As a result, it will crack faster and age prematurely.
Accelerants can influence how fast concrete cures, but it does so at the price of the quality of the concrete slab.
5. Wind Speed
One final factor that influences the speed of curing concrete is wind speed.
On windy days, water is more likely to evaporate fast.
The wind is pulling the water with it.
You’ll want to use plastic sheeting or another material to cover the concrete and protect it from the wind.
Strong winds can also make applying water and chemicals difficult.
It can direct the spray elsewhere to reduce full coverage.
You may think that you covered all of the concrete with the sprayer, but there may be spots that the wind kept the droplets from applying themselves.
You can use concrete slabs as fast as a day or two if you want to stop the curing process.
Doing so can result in a weaker slab of concrete compared to one that is allowed to cure for 180 days.
Certain processes and factors can make curing concrete easier or more difficult.
Consider these processes and factors when figuring out how to best cure your concrete slab for maximum compressive strength.