The term “curing time” is used to refer to how long it takes something to fully cure, undergoing a series of chemical reactions which allow it to set, harden, and develop traits which will allow it to persist for weeks, months, or years. A number of substances undergo curing times, including paints, epoxies, glues, resins, concrete, and so forth. Several factors can play a role in the curing time of a product, and these factors must be considered when applying it.
Concrete is often used in examples of curing time. When concrete is first poured, it is in a liquid to sludgy state. In the early stages, people could draw lines or make marks in the soft concrete and it would settle back in to fill them. Over time, the concrete cures, growing harder and harder until it reaches the final point, at which point it is a tough matrix of crystallized materials which are strong enough to allow people to walk, drive, and support buildings on the finished concrete.
If concrete curing goes wrong, however, the finished material will lack strength. It can be brittle and prone to fractures, and it may develop problems over time. Some issues which can affect concrete curing include heat and ambient moisture. Concrete actually cures best in muggy cool to neutral weather; if the weather is dry and hot, the hydration process which happens inside the concrete does not proceed as it normally does, weakening the concrete during the curing time.
Likewise, heat and moisture can have an effect on curing times of other materials. As people have noticed after painting, for example, when the weather is muggy, the paint takes a long time to cure, and sometimes it fails to set up altogether. Pressure can also be an issue, as can exposure to ultraviolet radiation. All of these factors can change the chemical reaction going on inside the material as it cures, changing the way it cures and having an impact on how it looks at the end of the curing time.
The volume of material is also an issue. A single poured concrete sidewalk takes much less time to cure, for example, than a dam. This must be accounted for when estimating curing time, as it is important to avoid disturbing the site while it is curing. For example, if stress is put on an epoxy joint before it cures, it can create hairlines fractures which weaken the joint, allowing it to fail in the future.