Mineral Composite Plaster Containing Hollow Glass Microspheres and CSA Cement for Building Insulation

Renovation of old buildings plays a key role in the sustainable energy transition because they are often poorly insulated and, therefore, lose a lot of heat through walls and ceilings. An important measure of renovation is façade insulation. Established and widely used materials include rigid expanded polystyrene (EPS) and extruded polystyrene (XPS) insulation boards. However, these boards do not easily follow the form of non-planar surfaces such as individually formed, ornamented, or bent façades. Furthermore, fire protection of these boards requires the addition of, for example, hazardous brominated flame retardants that impede recycling. This paper investigates a novel alternative insulating composite plaster. It is purely inorganic and can be applied easily by casting or wet spraying to any wall or ceiling element. The composite material consists of only two components: micro hollow glass microspheres as the insulating light component and calcium sulfoaluminate cement as the binder. Various compositions containing these components were cast, hydraulically set, and characterized with respect to microstructure, phase development during hydration, and thermal conductivity. With an increasing amount of hollow glass spheres, the density decreased to less than 0.2 g·cm−1, and the thermal conductivity reached 0.04 to 0.05 W·m−1K−1, fulfilling the demands of building insulation.