The difference in nomenclature between stucco, plaster, and mortar is based more on use than composition. Until the later 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 later part of the nineteenth century, Portland cement was added with increasing frequency in an attempt to improve its durability. At the same time, traditional lime plasters were being replaced by gypsum plaster.
Stucco used as an exterior coating on a residential building.
Traditional stucco is made of lime, sand, and water. Modern stucco is made of Portland cement, sand, and water. Lime is added to increase the permeability and workability
of modern stucco. Sometimes additives such as acrylics and glass fibers are added to improve the structural properties of the plaster. This is usually done with what is considered a one-coat stucco
system, as opposed to the traditional three-coat method.
Lime stucco is a relatively hard material that can be broken or chipped by hand without too much difficulty. The lime itself is usually white; color comes
from the aggregate or any added pigments. Lime stucco has the property of being self-healing to a limited degree because of the slight water solubility of lime (which in solution can be deposited in cracks, where it solidifies). Portland cement stucco is very hard and brittle
and can easily crack if the base on which it is applied is not stable. Typically its color was gray, from the innate color
of most Portland cement, but white Portland cement is also used. Today's stucco manufacturers offer a very wide range of colors
that can be mixed integrally in the finish coat.