The standard applies to external rendering systems which consist of coordinated thermal insulating undercoat and waterproofing finishing coat and are applied to solid walls and ceilings made of mineral building materials, e.g. especially masonry, concrete, reinforced concrete and leightweight concrete with porous structure. The undercoat as well as the finishing coat shall be made of factory made mortars according to DIN 18557. The factory made mortar for the undercoat shall be made of mineral binders and contain at least 75 volume percent of expanded polystyrene (EPS) as aggregate to satisfy the required thermal insulating requirements. The finishing coat shall resist weather as well as mechanical actions and shall be made of mineral binders and mineral aggregate.