Abstract:  
           
          Construction of ecological buildings has one specific sub-segment 
          - construction with natural materials. These are buildings 
          made of timber, earth, stone, straw bales, reed, hemp, etc. The majority 
          of these materials need protection against external effects. Architectural 
          or structural elements (roofing overlaps etc.) provide passive protection. 
          Outdoor plasters may be used as an active protection element. 
          The practice to-date has mostly applied lime plasters with high demands 
          for treatment during the first two to three months. An alternative choice 
          were unstabilized earthen plasters with high demands for maintenance. 
          The research intention, therefore, was to develop an outdoor plaster 
          based on natural materials resistant to external weather effects. 
          The desired solution was a plaster of unburnt earth with slightly modified 
          properties, mainly in reaction to water. In the first phase of research, 
          extensive literature search, dozens of potential stabilizing agents were 
          shortlisted. The selection criteria were: water resistance plus low diffusion 
          resistance of the resulting material, improved strength characteristics, 
          a zero effect on colour and appearance etc. Many alternative agents 
          were rejected. 
          Positive results were reached with special types of polymer binders applied 
          in small doses into earthen plasters. It must be emphasized that it 
          is the plaster quality that plays a significant role here (the analysis would 
          provide a topic for a separate article). The plaster is also suitable for repairs 
          and reconstructions of historical earthen structures. 
          These plasters are protected by a utility model. 
          Outdoor earthen plasters were first introduced to the Czech market at the 
          end of 2009. 
          Keywords: 
             
            earthen, plasters, 
            outdoor, clay, polymer, 
            stabilize, adobe 
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