# Humidity Conditions of Aerated Concrete Walls Depending on the Type of Finishing Coating
## 1 Introduction  
The extraction, transportation, and combustion of energy resources has a significant negative impact on the environment. Therefore, during the operation of buildings throughout the entire life cycle of the building, it is necessary to strive to reduce energy costs for heating. To do this, it is necessary not only to design energy-saving enclosing structures, but also to strive to ensure that excess moisture does not accumulate in the enclosing structures during operation. Excess moisture increases the thermal conductivity of building envelope materials and causes their premature destruction. The tightening of energy efficiency requirements for newly erected buildings has caused an increase in the volume of construction using lightweight concrete, both in the construction of private houses and in the construction of apartment buildings. Currently, various types of lightweight concrete are used: air-entrained concrete, aerated concrete, and silicate concrete, etc. [1; 2; 3; 4]. Now, in construction, aerated concrete is the most common; therefore, the humidity regime in walls made of this material is studied in detail in this work. The construction of buildings using aerated concrete involves the application of a decorative finishing layer. To prevent excessive moisture and maintain the heat-shielding qualities of aerated concrete, it is important to consider the vapor permeability of the finishing layers [5; 6; 7; 8; 9; 10; 11]. Excess moisture in the wall not only worsens the heat-shielding qualities of aerated concrete, but also reduces its service life. Especially dangerous is the accumulation of moisture at the border of the aerated concrete's external finishing coating. If a significant amount of condensate falls in this area, the external plaster collapses, cracks, and peels off the wall. Due to the temperature difference between the outdoor and indoor air in winter, mechanisms are launched based on the partial pressure gradient of water vapor that occurs during this time. There is a diffusion of steam through the building envelope, from the heated room to the street. To reduce the amount of condensing moisture, the materials in the wall must have less thermal conductivity and greater vapor permeability when moving from indoor air to outdoor air. Therefore, plaster intended for exterior finishing of aerated concrete buildings should be characterized by relatively high vapor permeability and low thermal conductivity. They should not interfere with the movement of moisture inside the wall. When it comes to exterior finishing systems for cellular concrete walls, plaster compositions are used that meet the requirements outlined in regulatory documents. These compositions have a vapor permeability resistance (for thick-layer plaster-based finishes) of no more than 0.5 m\({}^{2}\) h Pa/mg, for thin-layer plaster-based finishes and finishes without plaster layers, the vapor permeability resistance should not exceed 0.2 m\({}^{2}\cdot\)h\(\cdot\)Pa/mg. Additionally, these compositions have a water absorption rate with capillary suction of no more than 0.5 kg/(m\({}^{2}\cdot\)h\(\cdot\)0.5) and an adhesion strength \(R_{\mathit{adg}}\) (adhesion strength of the coating with an aerated concrete base) to cellular concrete of at least 0.15 MPa. The contact zone should also have a frost resistance rating of no less than F35 (the minimum number of freezing and thawing cycles, established by the standards, in the coating samples tested according to the basic methods, in which the original physical and mechanical properties are maintained within the normalized limits). Currently, there are several plaster options available on the domestic market for finishing cellular concrete, including Ceresit CT 24 and Ceresit CT 24 Light plasters from Henkel, Knauf-Grunband, Isoputz Extra plasters from Knauf, ATLAS KB-TYNK plaster from ATLAS, \"VERMIX IIIH50\" and \"VERMIX IIIH25\" from REMIX, and \"Pobedit perlite TM-30\" from Pobedit [12; 13; 14; 15].