Many professional and DIY construction projects today utilize concrete is some shape or form. That’s no surprise given the material’s exceptional versatility and affordability when used in large volumes. All things considered, it isn’t exceptionally hard to use, either. So long as you use the right mix ratio and mixing technique, even a novice DIY can have workable concrete in a matter of minutes.
But regardless of skill level, one part of the concrete construction process continues to confuse even the most experienced contractors – the curing process.
Herein, you’ll learn about the differences between setting, curing, and drying when it comes to concrete. You’ll also learn about the factors impacting the curing process as well as the best methods for watering all kinds of concrete. In all, you should walk away from this guide with a renewed understanding of the importance of concrete curing – regardless of your project’s scale.
How Long Does It Take Concrete to Set, Cure, and Dry?
Before we jump into this analysis of concrete curing, let’s take a moment to define a few terms that are often thrown around when discussing this construction process.
First off, “curing” is a process that begins as soon as concrete is poured. During this process, the ingredients in the concrete bind together and form the eventual concrete structure. During this process, moisture in the mix escapes to the top, often over the course of about 28 days.
Meanwhile, concrete cannot be said to be “dry” even after that 28 day period elapses. Instead, concrete is only fully dry when it is almost entirely free of internal moisture. This process can take as much as 30 days for every square inch of concrete. However, the right conditions can decrease this timeframe significantly (as noted below).
As for “setting,” this term has different implications when discussing the application of concrete.
A slab of concrete may be described as “set” after moisture evaporates from its surface. Setting may also be defined as the time period in which curing and drying occur. To avoid confusion, though, drying and curing are usually discussed as separate processes.
Factors Affecting Curing Time
There are a variety of factors that may affect a concrete slab or structure’s curing time.
The most notable of these – moisture – plays a role at every step of the concrete application process.
If, for example, a concrete mixture has more water added than an average mixture, it will likely take longer to cure. However, an un-watered slab or structure may crack before curing properly because its internal structure was unable to form as anticipated.
Along the same lines, the precise location of a concrete structure’s moisture can make a significant difference in the quality of its curing. Moisture that is mostly at the base of the structure will cause the upper levels to crack prematurely, especially under pressure.
Too much water towards the surface level, on the other hand, can cause chipping to occur after the slab finishes setting.
As one would expect, sunlight exposure also has a direct impact on concrete’s curing time. Direct sunlight can draw moisture out fairly efficiently, whether that is desirable or not for the job at hand.
In the long run, it is often best to control ambient exposure to heat in this way by keeping an important concrete structure shaded while it sets. Though it is harder to control in this way, ambient moisture and humidity must also be accounted for when curing concrete.
Putting Weight, Walking, and Driving on a New Concrete Slab
Many DIYers look for a rule of thumb that can be broadly applied to all concrete applications when it comes to applying weight to a “finished” slab. Unfortunately, a single rule that applies to all applications of concrete does not exist, at least when it comes to applying weight to the structure.
A concrete slab can typically only bare weight safely after fully setting over the course of a month or more. Many professionals will estimate a concrete structure’s capacity to bear weight based upon the number of 30 day periods that have elapsed since it was poured out.
These periods also account for weather conditions during the curing period, which may allow a structure to bear weight sooner or later than on average.
If you are a DIYer, your best bet is to follow the recommendations for waiting periods prescribed by the concrete mix you are using. Many manufacturers print such recommendations on the concrete mix bags or publish them online. If these recommendations are followed, you should be able to put weight on your new slab without much delay.
Speeding Up the Curing Process: Tips & Tricks
Depending on the parameters of your concrete project, you may eventually need to speed up the process.
Doing so has its benefits in terms of efficiency. However, it must always be balanced against the drawbacks of rushing this important formation process. Even so, these following methods can be used to expedite the concrete curing process:
- Only pour in good weather: You’ll find that your concrete cures much quicker if it is allowed to dry in ideal weather conditions. As such, you should try to schedule your concrete pours during time periods that are sunny with minimal humidity. Though some rain can be permitted during the curing process, too much shade from cloud cover can slow down the process in the long run.
- Add calcium chloride to the initial mix: This is a well-known concrete additive that can be added to a concrete mix before it is poured. It allows water to more efficiently escape a drying concrete slab, which in turn allows curing to complete within a tighter time frame. Be sure to follow manufacturer recommendations when using this additive, though, so that you don’t harm the resulting slab’s structural integrity.
- Cover with a plastic sheet: In super sunny environments, evaporation can cause moisture to escape too quickly during the curing process. To counter this, plastic sheeting can be placed over the new concrete slab so as to trap any evaporating moisture. This can help keep a slab’s curing on schedule, despite the environmental circumstances.
Watering Concrete: Why and How Should It Be Done?
Many folks think curing concrete is all about letting moisture escape a freshly-poured slab. But in truth, curing cannot occur properly unless moisture levels in and on the slab are properly maintained. This is why many professionals water their concrete while it cures.
There are several methods for doing this, which are as follows.
First up is the so-called “moist curing” which requires an individual to cover their freshly-poured slab in water 5 to 10 times a day. This prevents too much moisture from escaping the slab, particularly from direct sunlight and ambient heat.
There is also “pond curing,” which requires the DIYer to create temporary berms around the target slab. That space is then flooded, allowing for less frequent water applications.
When watering your concrete, keep an eye on your upcoming forecast. If any cold weather below 50 degrees or so is expected, try to minimize watering before that cold front arrives. Cold or even freezing water can severely impact a slab’s strength as well as its surface’s stability.
There’s no doubt that concrete curing is a bit of a precision process. But even if you are a DIYer, you can learn to apply concrete and allow it to properly set using the professionally-recommended guidelines set forth in this guide.
While your results are never assured, there’s a much better chance that your next concrete slab will turn out strong and aesthetically-pleasing if you hold fast to these proven recommendations.