Clay mortars, as low-processed materials, are often used as internal plasters in natural construction. In order to improve their thermal insulation properties, lightweight aggregate or porous organic components are often added. Such additives as hemp shives can also improve other properties, e.g. reduce shrinkage or improve bending strength. Clay parameters can be modified, for example, using biopolymers. An example is acid casein, which in combination with lime forms casein glue used, among others, to improve mechanical strength and water resistance. The aim of the work is to perform basic tests of mechanical and physical properties of heat-insulating mortars based on a clay binder with the addition of hemp shives and an admixture of casein. Flexural and compressive strength, density, total porosity, shrinkage and thermal conductivity coefficient are measured and discussed.

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