There is no short answer to this question. How long a piece takes to cure depends on several factors: the mix you use, how dry the environment is, and the temperature. We will explore those now.
Why is curing cement art one of the most critical aspects of the creation process? Because if you fail to cure your piece correctly, it will be weak, and you will end up with a broken part. The curing process requires time, patience, and practice.
Concrete curing ensures sufficient moisture in concrete within a preferred temperature range to assist cement hydration. The best temperature for the room it is curing in is between 55 and 90 degrees Fahrenheit. If it is colder than that, it will take much longer to set and several days longer to cure.
The cement hydration process occurs between cement and water, the reaction is exothermic, meaning it releases heat, so if it is too cold, the concrete does not correctly cure and can be brittle. If it is too hot, the concrete can flash cure, and it will not have enough moisture to maintain strength, making it crack.
The process isn’t instantaneous and requires monitoring to ensure sufficient moisture and temperature is favorable for this chemical reaction. The larger the piece, the more closely you need to monitor it. Larger pieces heat more quickly and do better at a constant temperature of 60-70 degrees Fahrenheit.
It also helps to have a room with at least 80 to 85 percent humidity. The humidity in the room assists with keeping the concrete from drying out during the setting process but is not enough to keep it hydrated during the curing process; for that, you need to physically immerse the piece in water for the strongest possible result.
Properly curing your art piece will prevent the concrete from drying, cracking, or shrinking, eventually causing deterioration.
What happens during the Hydration Process?
Mixing cement, water, and aggregate together make a workable paste. It can be molded to the desired art form and then left to set or poured into a mold and left to harden. The type and amount of aggregate will affect the water you need.
If you use something that absorbs moisture, you will need a lot more water, and it can often make bubbles, making your piece weaker. If you use something like pea gravel or sand that is non-porous, it will not affect the water intake, but it can be harder to ensure the moisture is correct. Mix the concrete mix and water first to get the right consistency, then add the non-porous additive.
A common misconception is that concrete needs to dry to harden. It doesn’t dry; it sets. Setting happens when the powder is fully in contact with moisture and has time for the chemical reaction.
Concrete requires a smaller amount of moisture to set, then even more, to hydrate and cure properly. When the concrete dries, it stops getting stronger; you can add strength by letting the piece cure in water, so it is as strong as possible.
Concrete with too little water in the setting process may dry but not fully react, leaving weak spots within the concrete. Putting the piece in water for the curing process will not fix the problem, but adequately mixed concrete will benefit from the soak.
Just like water is necessary for our survival, the reaction of water with concrete is paramount for creating greater strength in the structure.
You also need to ensure not to add too much water into the mix, or you will get bubbles, which will be fragile. An excellent way to ensure you have the right amount of water is that the mixture will be about the thickness of toothpaste and turn liquid on top when tapped/vibrated.
After the concrete is set, you can immerse the entire piece in water for 24 hours to strengthen it as it cures.
How long do you cure concrete statues and art before painting?
This depends on the concrete mix you use; some take 2-4 hours to set, but most take at least 24 hours to cure.
If you immerse the piece in water as it cures, the piece will be stronger, but it is essential to wait until the concrete has a fuller set before you put it in water. A basic rule of thumb is to let the concrete sit in water for 24 hours, then let the piece rest for a week before painting.