The aim of this paper is to study possibilities to obtain composite materials using organic rich lake sediments (further – sapropel) and lime as binders and hemp shives, wood fibre, and wood sanding dust as fillers. The mechanical and thermal properties of the obtained composite materials are investigated and compared to similar composites, such as lime-hemp concrete (LHC) and magnesium oxychloride hemp composite (MHC). Because of the high amount of organic content these materials are prone to biodegradation, therefore the materials were coated with ALINA LIFE TM organoclay additive that helps to extend product life-time, reducing rate of biodegradation. The effect of the coating on the resistance against fungi Alternaria alternata and Cladosporium herbarum was investigated in two conditions: before and after experimental accelerated ageing of materials in climate camera. Results indicated that the composites made of sapropel and lime have similar mechanical properties as LHC and MHC: compressive strength of 0.77 MPa for sapropel-lime binder compared to 0.90 MPa for LHC and 1.12 MPa for MHC. As organoclay additive provided higher resistance to biodegradation, sapropel-lime composites have shown sufficient amount of positive properties to be considered for application in construction material industry and as an object for further research.