Abstract. Composite binder consisting of cement (55%), acid fly ash (40%) and limestone (5%) has been designed. It is obtained by co-milling to a specific surface of 550 kg/m², it has an activity of 77.3 MPa and can produce a more dense cement stone structure. Integrated study revealed that the concrete on the composite binder basis provides an effective diffusion coefficient D. So we can conclude that the concrete layer protects buildings from toxic effects of expanded polystyrene. Low water absorption of the material (2.5% by weight) is due to the structure of its cement stone pore space. Besides lime powder prevents the penetration of moisture, reduces water saturation of the coverage that has a positive effect on useful life period. It also explains rather low water vapor permeability of the material -0.021 mg/(mhour-Pa).