Delays in concrete curing are a major issue on construction sites. If the concrete isn’t dry by the time coating work is scheduled to begin, it often sets the entire project schedule back. This, in turn, causes chaos across the site and frequently results in additional costs. Unfortunately, sometimes under pressure, people end up applying the finish to wet concrete. This, in turn, can expose the building to moisture damage, causing inconvenience to residents and repair costs for the construction company. That is why it is important to pay attention to concrete drying right from the very beginning. Here, I’ll go over our own observations regarding what factors have led to delays in concrete drying on the job site and how the drying process can be accelerated.
Why does concrete take longer to dry?
The factors affecting concrete drying can be broadly divided into four categories: design, casting, on-site drying conditions, and water damage.
Design
The design phase is perhaps where the drying of concrete can be influenced the most. It all starts with a realistic schedule. If the schedule is too tight in relation to the concrete’s drying time, even minor deviations can cause chaos on the job site. The concrete drying schedule should be taken into account during structural design, in addition to other requirements. Thick concrete layers dry more slowly than thin ones. Structures that dry in one direction also dry more slowly than those that dry in two directions.
The choice of concrete mix also has a major impact on the curing schedule. It is advisable to work closely with the concrete supplier when developing the concrete mix design. The goal should be to use concrete with a low water-cement ratio that still retains the workability required for the job. This ensures that the concrete delivered to the site already contains as little water as possible from the start. When the schedule is tight, it is also advisable to choose a fast-drying concrete.
Casting stage
The pouring stage is also very important for the curing of concrete. Stiff concrete is easier to work with when water is added to it. However, this can delay the drying of the concrete by up to several months. Instead of water, concrete plasticizers developed specifically for this purpose should be used. The aggregate size of the concrete also has an effect. A concrete mix with large aggregates and a high solid content dries faster than one with small aggregates. It is also important that there are no puddles or other excess moisture beneath the pour. Furthermore, in layered pours, such as slab or surface concrete pours, pouring over concrete that is too wet can significantly delay drying.
Conditions
The first thing you should do after pouring the concrete to speed up the drying process is to grind away the cement paste from the surface of the concrete. However, grinding should not be done until after the curing process is complete, to allow the concrete to harden.
Even if all of the above factors were in perfect order, the concrete might still not dry at all unless the drying conditions are adequate. The most critical factor in drying conditions is the relative humidity of the air in contact with the concrete. The relative humidity of the air must be lower than that of the concrete so that the concrete can evaporate water into the air. This, in turn, is achieved by ensuring that the air is warm enough to absorb sufficient moisture, as well as by ensuring air circulation and ventilation. Concrete will not begin to dry until the space is sufficiently heated, ideally to about 20–25°C. In the summer, when the outside air is humid, ventilation should be minimized by keeping doors and windows closed and using dehumidifiers indoors to remove excess moisture from the air.
Naturally, the temperature of the concrete also affects the drying process. Warm concrete releases moisture more efficiently and dries faster. Concrete can be heated from the inside using underfloor heating. To dry concrete quickly or under difficult conditions, there are also drying channels designed for this purpose, which are installed in the structure during the pouring phase. From the outside, concrete can be heated using, for example, panel dryers.
Dirt and dust also slow down the drying of concrete. It is therefore important to clean the construction site regularly, as this speeds up the drying process. Site logistics must also take concrete drying into account. Excess material on top of the concrete effectively prevents it from drying. It is therefore important that surfaces intended to dry quickly be as free of materials as possible, allowing drying to occur unimpeded.
Construction sites are often in a rush to apply a finish to areas where the concrete is sufficiently dry. What is often overlooked is that this can slow down the drying process in adjacent areas. This is because, even after coating, the concrete continues to dry for a long time, even when it is dry enough for coating. When the concrete’s natural drying path is blocked by the coating, the moisture remaining in the concrete seeks a new path to escape the structure. In this case, the moisture begins to migrate laterally into areas that have not yet been coated. This, in turn, causes the moisture content in the concrete of these areas to rise, and drying can be significantly delayed. Therefore, from a drying perspective, it would be sensible to apply the coating only after the entire pour has been confirmed to be dry.
Water damage
Unfortunately, water damage often occurs at construction sites. Water damage can be caused, for example, by a burst pipe or inadequate protection. When concrete gets wet, it naturally takes longer to dry. NP concrete, in particular, can be very difficult to dry if it gets wet due to its special properties.
Most water damage in new single-family homes is related to pressure testing. Naturally, similar problems also occur in other types of buildings. The most common location is the manifold connection. It is therefore advisable to schedule pressure testing for the morning and, preferably, not right before the weekend. This makes it easier to address any potential issues if the pipe connections leak.
It all comes down to execution
Ultimately, concrete curing is a very simple process. When all of the above factors are taken into account from the very start of the project, the site often cures well on schedule or even well ahead of schedule.
If you need help with concrete curing, please contact us—together we’ll find a solution! Check out Moisture Measurement and Environmental Monitoring -our services.
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