Everyone from contractors to engineers has wrestled with the curing component of concrete. It is the most important step in laying concrete cement to ensure its longevity and durability, but is often the biggest misstep of the concrete project. Curing concrete improperly will lead to cracks and lifts and drops in the concrete slab leading to costly, time consuming repairs and even lawsuits.

To achieve the vast attributes of concrete, such as durability, strength, water resistance, and resistance to freezing and thawing, concrete must endure a chemical reaction called hydration. A delicate balance between water and temperature is important to the hydration process. On average, the best temperature for curing concrete is between 50-70 degrees Farenheit, easy to achieve if your project is indoors, not so easy when working outside in the elements. So paying attention to the factors which affect the curing times is key to a successfully cured concrete slab.

What is “curing”?

Curing is the method in which the concrete retains its warmth and moisture throughout the hydration of the cement. Properly hydrated concrete dries evenly throughout, creating a seal between the cement and the sand or silica additive, creating a tough tight surface which resists damage.

What are the factors which affect the curing time of concrete?

– Temperature- Between 50-70 degrees Farenheit is perfect for proper hydration while curing.
– Humidity-Low humidity or arid environments make the drying process quicker
– Wind-Can evaporate the hydration process leading to a quick dry.
– Cement type- Pozzolanic cement or concrete admixed with pozzolanic material is required to be cured for a much longer duration. Mass concrete projects, heavy footings, large piers and abutments should be cured for at least 2 weeks.

What is the best method used to cure concrete properly?

Water is the best method for curing concrete. Water allows for the promotion of hydration and eliminates shrinkage.

Can you pour water over the surface of the concrete to prevent drying?

If this is done within the first 2 hours on the project, there may be interference with the water cement ratio of the concrete and can breakdown the stability of the concrete. It is true that concrete should never be allowed to dry fast, so placing wet burlap over the area will ensure moistness without the droplets of water, and lead to a perfect cure of the entire concrete slab. This process must be done for an entire 24 hour period for proper setting time. After the 24 hour setting time, there is no more risk to upsetting the water to cement ratio, so adding water by ponding or spraying is easy and without risk.

What are the different types of water curing?

Water curing can be achieved is several ways:

-Ponding- This is referred to as thermal curing, it is the process of applying a large amount of water over the entire area of concrete to prevent weather influences in large outdoor areas.
-Spraying- Involves liquid membrane-forming compounds sprayed onto the surface which are effective, economical moisture barriers for moist-curing concrete.
-Wet covering- This basic principle is the application of a plastic sheet over a freshly concreted area, to avoid air flow on the affected area. Air flow leads to evaporation, and thusly poor curing.

How long do you wait in order to achieve cured concrete?

This is a tough one to answer since there are many different factors as listed above. However, the general rule for curing concrete properly is waiting until the concrete is dried to about 70-75% of the desired strength, before hydration is stopped.

Curing concrete is a fickle endeavor for even the most experienced engineer. The slightest miscalculation could be the difference between longevity and economic breakdown. These informational tips are just that, tips. It is always best to ask experienced pavers/engineers to check your numbers before plowing ahead with your concrete project.

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