The difference in nomenclature between stucco, plaster, and mortar is based more on use than composition. Until the latter part of the nineteenth century, it was common that plaster, which was used inside a building, and stucco, which was used outside, would consist of the same primary materials: lime and sand (which are also used in mortar). Animal or plant fibers were often added for additional strength. In the latter nineteenth century, Portland cement was added with increasing frequency in an attempt to improve the durability of stucco. At the same time, traditional lime plasters were being replaced by gypsum plaster.