In Finland there’s a strong belief that when drying concrete you only need to measure the humidity in the concrete itself. But this is wrong, for two reasons.
To avoid mold problems, it’s extremely important for concrete structures to dry sufficiently before finishing. However, concrete drying is a slow and complicated process. It usually takes weeks or even months for a concrete slab to dry. In Finland it’s often thought that the best way to measure drying is to place moisture sensors inside the concrete.
There are two problems with sensors that are installed into a concrete slab.
Measuring relative humidity from inside the concrete slab only provides information on the effects of drying. It doesn’t tell you how efficient the drying is or why it is failing or succeeding. For example, one measurement might tell you that the moisture content inside the concrete is 95%. Then the next week, you get exactly the same result: 95% humidity. An in-situ concrete slab sensor doesn’t tell you why the concrete hasn’t dried at all in a week.
Often people think the humidity sensors placed inside the concrete can be used, after construction is complete, to measure changes in humidity in the finished building. In theory this sounds like a good way to monitor for water damage. The problem is that the critical locations that need to be monitored during construction are not the same as the critical locations that should be monitored in a finished building.
The main danger points where water damage can happen in an occupied building include kitchens and bathrooms, ie places where water is used. During construction however the danger points are different. For example, a deep slab that’s been laid on-site. These slabs usually have nothing to do with water faucets, and there’s no need to monitor them once they’re dry.
Air temperature and humidity must be monitored if you want to dry concrete effectively
To get concrete structures to dry effectively, you need to monitor the ambient air temperature, ambient relative humidity and air pressure around the concrete. Air temperature and humidity have a significant effect on the concrete drying process. If the conditions are not conducive to drying, the concrete slab may not dry at all no matter how much time passes.
For example, a floor structure for a bathroom consisting of insulation + hollow slab 265 mm + tilted slab 115 mm, will dry to a target moisture content of 90% in 8 weeks at an ambient temperature of 15°C with a relative ambient humidity of 70%. At 20°C and RH 50%, the same structure will dry in just five weeks. The example is calculated with the Finnish Concrete Association’s “BY 2020” calculator.
When you monitor air temperature and humidity you can understand why a concrete slab is not any drier than it was a week ago. For example the air temperature could be too low, in which case you need to heat the site more. With data on ambient conditions you can make proper decisions about site heating and air drying.
When you a construction site’s ambient conditions are regularly monitored and optimized, it is possible to get concrete to dry according to schedule. It also makes it easier to predict when the slab will be dry enough for finishing.
Real-time remote monitoring will revolutionize the industry
It’s already possible to monitor site conditions with real-time, remote sensors. Real-time temperature and humidity as well as detailed history data can be checked without needing an on-site visit.
Kaltiot provides a complete solution for monitoring air temperature and humidity on construction sites. Real-time monitoring allows for more efficient and optimised drying and heating during construction.
