There have been many news stories lately about moisture-related problems even in brand-new buildings. Moisture damage can occur as a result of water damage, such as when a water pipe bursts. Applying a finish to a concrete structure too early, before the concrete has dried sufficiently, can also cause moisture damage. In this blog post, I’ll discuss what a homebuilder should do to ensure that the concrete dries effectively and that finishing work can begin safely and according to the construction schedule.

Factors affecting concrete drying

Many factors affect the drying of concrete, such as the aggregate size of the concrete, the water-cement ratio, the additives used, ambient air conditions, concrete temperature and thickness, as well as the cleanliness of the job site. Here, I’ll highlight a few of the most important ones and explain how a homebuilder should take these into account in their own project.

Water-cement ratio of concrete

The most important factor affecting the drying of concrete is the water-cement ratio of the concrete used. This indicates the ratio of cement to water in the concrete. The lower the water-cement ratio, the less water there is in a cubic meter of concrete. A cubic meter of concrete with a high water-cement ratio can contain up to 100 liters more water than concrete with a low water-cement ratio.

Before pouring the floor, it’s a good idea to take a moment to choose the right concrete mix. It’s best to discuss the concrete mix with your concrete supplier, as they are experts in concrete and can develop a mix design suitable for your project. The properties required of good concrete include a low water-cement ratio, aggregate particle sizes suitable for the pour, and sufficiently good workability to ensure the floor is poured properly. After pouring, it is important to follow the curing instructions provided by the concrete supplier.

Even though higher-quality concrete costs a little more per cubic meter, this is not an area where you should skimp!

Indoor temperature and humidity

Since concrete dries by evaporating the water it contains into the surrounding air, the temperature and humidity of the indoor air at the construction site play a major role in the drying process. If the air inside is cold and humid, evaporation does not occur. On the other hand, when the air is warm and dry, evaporation is rapid.

Indoor air drying conditions can be measured using two parameters: temperature and relative humidity (RH). As a rule of thumb, drying conditions are good when the weekly average air temperature is +20 °C and the relative humidity is 50% or less.

Creating good indoor air quality

For most of the year, good drying conditions can be achieved simply by ensuring adequate heating. When it’s cool outside, raising the temperature to around 20 degrees is enough to ensure that the indoor air is sufficiently dry and that the concrete can release moisture.

During the summer, when it’s warm outside—and especially in late summer, when it’s often humid as well—heating alone is no longer enough (unless carpenters enjoy working in 35°C heat). In such cases, dehumidifiers must be used. When using dehumidifiers, it is important to keep doors and windows closed, otherwise humid air will flow in from outside and the dehumidifiers will be of no use.

When creating drying conditions, it is important to remember that temperature and humidity are monitored as so-called weekly averages; in other words, the key requirement is that, on average over the course of the week, conditions remain at least +20 °C and below 50 %RH. Occasional trips to bring in building materials won’t tip the scales just yet. However, it’s important to ensure that heaters, fans, and dehumidifiers are running at least at night and on weekends! You can monitor air temperature and humidity using remote-readable environmental sensors, for example.

Air circulation

Air circulation on the construction site should be managed so that air is drawn in at point A and blown out at point B on the opposite side of the building. If the building has multiple floors, air should be drawn in from the lower floor and exhausted from the top floor. At least one heater should be placed near the air intake so that the cool air coming in from outside is warmed immediately upon entry.

The goal is for the air to flow from point A, circulating as thoroughly as possible through all the different rooms and absorbing moisture from the concrete along the way. Finally, the moist air is blown out at point B. The exhaust air can be vented out, for example, using a temporary duct fan installed in the range hood duct.

Cleanliness of the construction site

Dirty floor surfaces or storing building materials on the floors also significantly slow down the drying process. Water cannot evaporate from the concrete if the surfaces are covered by a thick layer of dust and sawdust or if stacks of drywall are stored on the floor. Building materials must always be stored off the floor, e.g., on pallets.

Determining readiness for paving through moisture measurement

Here are some quick tips for successfully drying concrete:

By following these instructions, you can ensure that your job site has optimal drying conditions for concrete and that the drying process proceeds quickly.

As the paving date specified in the construction schedule approaches, the concrete’s sufficient dryness must be verified using an appropriate using moisture measurement.

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