Drying behavior of screed products

© Fraunhofer IBP

Observation of the drying-rate curve of a screed sample in the climate simulator at Fraunhofer IBP

© Fraunhofer IBP

With the aid of material characteristics determined in the laboratory, drying behavior can be predicted using mathematical methods (in this case, the WUFI® Pro building component simulation software). The graph shows changes in temperature and humidity recorded at a specific point in the simulation of a floor structure with XPS insulation.

In most cases of water damage to buildings, floors are the most seriously affected. Standing water on the surface seeps into the underlying screed, which quickly becomes saturated if the surface water is not evacuated immediately. Before a new floor covering can be laid, allowing the building to be used as before, the screed has to be replaced or dried. To determine the drying rates of different screed products, researchers at Fraunhofer IBP have conducted numerous laboratory tests to establish the material characteristics of numerous screed products and their drying behavior. The findings of these tests make it possible to calculate the drying-rate curves and drying duration for different types of screed.

Floor screeds have a high water content after they have just been laid or after water damage. This can lead to high indoor air humidity levels and to the growth of mold on surfaces and in hollow cavities. Wet screed therefore needs to be dried before a new floor covering is laid and the building can be reused. The drying rate depends on the drying method, but even more on the type of screed product employed. To be able to predict the drying-rate curve and drying time for different types of screed, various material characteristics were determined in the laboratory and drying tests were carried out using different types of screed.

The tests were conducted on commonly used anhydrite screeds and flowing cement screeds. Each type of screed was prepared using different proportions of additives and binders. The results showed that, depending on the composition of the screed, the drying time could vary considerably, between approximately 4 weeks and six months.

It was also observed that material properties differed as a function of the thickness of the screed. For example, fine particles present in the mixture could rise to the surface and form a thin film that inhibited the drying process. A sedimentation process was also observed in which the mixture could separate into multiple layers, each with different characteristics. For this reason, the screed samples were tested layer by layer and the material properties were determined separately for each layer. This dependency on thickness must also be taken into account in mathematical calculations.

Using the knowledge thus obtained and the material properties determined, the researchers can now simulate the drying behavior of specific types of screed under a wide range of conditions, with the aid of hygrothermal simulation programs. If the composition of the screed is known, it is also possible to carry out more precise tests of various drying methods employed to accelerate the drying process.

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