## 2 Materials and Methods
### Conventional Measurement Tests  
Hygroscopic and porous materials bind moisture in their structure, depending on the relative humidity of the environment. There is an equilibrium moisture content for a certain state of ambient humidity in building materials. It represents the amount of moisture that had stabilized in the material under the given conditions. The determination of equilibrium moisture in building materials is commonly conducted using two conventional methods [36]. Desiccator methods can be considered as the most well-known and widespread. The desiccator should be placed in a constant temperature environment, as some solutions significantly change the water vapor pressure above the saturated aqueous solution, even with small temperature changes. Figure 2a shows an example of a test with the desiccators placed in air-conditioned room. The second conventional method is based on the use of a climatic chamber that provides the environmental parameters to which the sample is exposed. The method is in principle identical to the desiccator method, where the sample is exposed to the intended environmental state. The difference is the samples are placed in a test chamber where they need to be weighed. The chamber should allow the handling of samples without opening it in order to avoid contamination from the environment; thus, to not affect the samples with the air of the laboratory. If this is not possible, lid-covered test dishes should also be used or the scale placed directly in the chamber and the samples handled via a hand-port. Both the mentioned conventional methods are standard according to EN 12 571 [37]. Identifying the interaction of a material with air humidity is often not limited to one state--one point of moisture equilibrium. These points tend to be investigated at a constant temperature and various relative humidities to quantify the wider area. The line connecting a set of such equilibrium points at a constant temperature represents the sorption isotherm. For building materials, these curves most often range from 30 to 95%, where these properties are the most important for building applications. At a higher humidity, there may be problems with biological attack or degradation of the samples; also, the growth of fungi and molds on their surfaces may arise. Although many building materials can acquire a humidity higher than 95% or 97%, their measurement is difficult to accomplish. At such a high relative humidity, even small change in temperature can increase the risk of moisture condensation on the surface of the samples, which again may  
Figure 2: (**a**) Rack with desiccators in an areconditioned room; (**b**) samples in an environmental chamber. affect the results of the experiment. The curves are basically detected in two modes. The sorption mode gradually saturates the material with moisture by increasing the relative humidity and determines the constant value of equilibrium humidity for each environment. On the other hand, the desorption regime is represented by a gradual reduction of the humidity in an environment. Both processes are very slow, and stabilization can take a very long time, especially for higher humidities. The desorption curve acquires greater values than the sorption curve. This provides the hysteresis and is attributed to several factors. Dried samples with dimensions of 100 mm \(\times\) 100 mm \(\times\) 20 mm were first placed in the lowest humidity environment. The weight was determined at regular intervals, and after stabilization the samples were moved to a desiccator with a higher humidity. After measuring the highest humidity, the process was repeated, applying decreasing ambient humidity. The measurement of each point took approximately two weeks. The laboratory temperature during the experiment was around 22 \({}^{\circ}\)C. The same samples were used for the measurements and for the determination of the bulk density. From the point of view of the standard procedure, the samples were not enclosed in pans with lids due to their shape and size.