Concrete sweating occurs when water droplets accumulate on the surface of concrete due to temperature differences between the surrounding environment and the concrete. This phenomenon can be troublesome as it can create a slippery surface and make the floor damp, posing safety risks and causing inconvenience. A sweating concrete floor can be particularly annoying and potentially hazardous in various settings, such as residential, commercial, or industrial spaces.
Fig 1: Concrete Sweating
Concrete sweating is the focus of our study in this article, where we delve into its causes and effective prevention methods. Concrete sweating, also known as condensation on concrete surfaces, is a common occurrence that can lead to a variety of issues. Understanding the root causes of concrete sweating is crucial in order to implement preventive measures effectively. By examining the underlying reasons for concrete sweating and implementing appropriate prevention methods, we can mitigate the negative impacts associated with this phenomenon.
Phenomenon of Concrete Sweating
Sweating Slab Syndrome occurs when warm and humid air enters a structure through openings such as doors, windows, and ventilators. The humid air diffuses itself inside the structure and condenses on any surface that is at or below dew point temperature, resulting in water droplets forming on the surface of the concrete.
For instance, if the ambient conditions within a structure have been at 70º F and 50% relative humidity for several weeks and the slab surface temperature is also close to 70º F, then a weather front with 80º F air and 90% relative humidity can trigger Sweating Slab Syndrome. As the moisture-laden air enters the building, any surface that is at or below 77º F will be at dew point, which can cause the concrete surface to sweat.
When the concrete surface is at dew point, the moisture in the air condenses on the surface where it is not easily absorbed, resulting in water droplets forming on the surface. This phenomenon is similar to what happens when the outside of a cold beverage container gets wet on a warm and humid day or the surface of a car gets wet when it is left outside on a cool and damp night.
Causes of Concrete Sweating
Concrete sweating, a phenomenon where moisture droplets form on the surface of concrete, is primarily attributed to temperature differentials. However, there are other factors that can contribute to concrete sweating as well. These additional causes can be just as important to consider in preventing or mitigating the issue.
In particular, humidity levels can play a significant role in concrete sweating. When the air is very humid, the moisture in the air can easily condense on the cool surface of the concrete. Additionally, poor ventilation in a space can exacerbate humidity levels, leading to more sweating.
The presence of water or moisture within the concrete itself can also contribute to sweating. This is often due to a lack of proper curing, which can leave excess water trapped within the material. As the concrete dries and the temperature changes, this moisture can seep out of the surface, leading to sweating.
Finally, the use of certain types of concrete mixes can also increase the likelihood of sweating. For example, mixes with a high water-cement ratio or low air content can be more prone to sweating. Similarly, concrete that is overworked during the mixing or placement process can be more susceptible to the issue.
Overall, while temperature differentials are a common cause of concrete sweating, it’s important to also consider factors like humidity, water content, and mix composition. By addressing these factors, it may be possible to prevent or reduce sweating and avoid any potential issues that can arise from the excess moisture.
1. Dew Point
The main reason for concrete sweating is the contact between warm and moist air with a cold concrete slab. When such air comes in contact with the cool surface of the concrete, the temperature of the air drops. If the temperature of the air drops to or below the dew point, then the air will start to condense on the surface of the concrete. This condensation leads to the wet and misty appearance of the concrete surface.
2. Due to Wet Adjacent soil
Retaining concrete walls, such as breast walls, often face the challenge of wet soil on the other side. Despite concrete being known for its solidity, hardness, and density, it contains tiny capillaries that allow water droplets to move through them, resulting in the phenomenon of concrete “sweating.”
Fig 2: Concrete sweating due to wet adjacent soil.
When the air temperature above the concrete is higher, any moisture present within the concrete can rise to the surface and evaporate. This process may result in a wet surface, especially if there is a significant amount of moisture within the concrete. Additionally, this evaporation process can cause efflorescence, which is the deposit of salts on the concrete surface, further contributing to the wetness of the surface.
3. Salts Deposits
Salts possess the characteristic of drawing moisture from the air as well as potentially from the concrete itself, owing to their hygroscopic nature. The deposition of salts can occur due to various factors, including internal sources within the concrete or external applications.
4. Density of Concrete Slab
Concrete sweating is a phenomenon that is not typically observed in the main concrete slab. This is because during the construction of the main slab, special attention is given to compaction and surface finishing to prevent this problem. However, this issue may arise in the pour-back strips located within the perimeter of the tilt-wall.
Upon conducting tests, it has been discovered that the porosity of pour-back strips is generally higher compared to the main floor. The reason behind this is that pour-back strips are often not finished in the same manner as the main floor. As a result, they may not have received the same sealer/densifier treatment that was used on the main body of the slab. This difference in treatment could be the reason for the higher porosity levels found in pour-back strips, leading to concrete sweating.
5. Cleanliness of Concrete Slab
The permeability of a concrete slab can be affected by various factors, one of which is its cleanliness. When a slab surface is covered with black rubber tire marks or exhaust deposits, its permeability can be reduced. This reduction in permeability not only makes the surface less absorptive to moisture from above but can also increase moisture levels within the concrete and near the slab surface over time if an effective vapour retarder is not present beneath the slab.
If a slab surface becomes less permeable due to the presence of rubber tire marks or exhaust deposits, it will be less capable of absorbing moisture from above. This can create a problem if an effective vapour retarder is not installed beneath the slab because moisture levels within the concrete and near the surface of the slab will rise over time. The buildup of moisture can eventually cause damage to the slab, leading to costly repairs.
To prevent moisture buildup within the concrete and near the surface of a slab, it is important to ensure that the slab remains permeable. This can be achieved by keeping the surface clean and free of rubber tire marks or exhaust deposits. If the slab is not permeable enough, an effective vapour retarder must be installed beneath it to prevent moisture from entering and accumulating within the concrete. By taking these steps, the lifespan of the slab can be extended and the need for costly repairs can be avoided.
Prevention Measures for Concrete Sweating
The preventive measures for concrete sweating are listed down below –
1. Good Housekeeping Practices
Maintaining cleanliness of concrete surfaces is crucial in ensuring the safety of employees and protecting assets. In order to achieve this, it is important to keep these surfaces free from any salts and deposits. One effective way to achieve this is by using commercial cleaning agents to scrub floors and vacuum machines. However, it is important to follow proper procedures to ensure that this cleaning is done safely and effectively. By doing so, you can ensure a safe working environment for your employees and protect your assets from damage.
2. Good Air Movement Within the Facility
When there is inadequate airflow inside a building, it can result in sweating slabs. This typically happens when the air inside the structure is unable to flow out easily. In such cases, it becomes necessary to de-stratify the air to improve the air movement inside the building. This can be achieved by installing an HVLS fan, which can help to circulate the air and prevent sweating slabs from occurring. By ensuring sufficient air movement, an HVLS fan can help to maintain a comfortable indoor environment and prevent moisture-related problems.
3. Use HVLS Ceiling Fans
HVLS fans offer a solution to reduce the temperature differential between the ceiling and the floor. In addition, they can increase the rate of surface evaporation, which is beneficial for maintaining a comfortable environment. These fans are an economical option for cooling structures while simultaneously preventing the accumulation of moisture on the floors.
4. De-Humidification Units
Dehumidification units can be employed to modify the indoor environment of a building, potentially mitigating or completely eliminating sweating slab syndrome. However, the use of such units can result in significant expenses, as they consume energy and may increase the building’s electricity bill.
5. Use Low-Permeance and Low-Slab Retarders
When products are stored directly on the floor, using mats can be a highly effective solution. Mats can help prevent moisture from rising and condensing underneath stored products, reducing the likelihood of damage or spoilage. This is especially important in environments where moisture levels are high, such as in basements or areas with poor ventilation.
By placing mats beneath stored products, businesses can create a barrier that helps to block moisture from the floor. This is especially useful for items that are sensitive to moisture, such as paper products or electronics. Mats also help to prevent mold and mildew growth, which can be harmful to both the stored products and the surrounding environment.
Overall, using mats as a preventative measure can help businesses to avoid potential damage and ensure that their products remain in good condition. It is a cost-effective and simple solution that can provide significant benefits in terms of product preservation and customer satisfaction.