The original interior surface of the opera house was gypsum plaster decorated with distemper. Whiles the opera house surfaces have been obliterated or covered over in most locations, the original plaster is still evident in the third floor, former balcony area. The salmon colored plaster visible below layers of flaking paint at the north wall is original, and in the third floor restroom, behind the later plaster skim coat that is falling from the walls, a portion of a painted frieze can be seen at the top of the wall. The frieze is a delicate yellow stenciled onto the salmon background, with floral and geometrical motifs.
At the time the opera hall was built, gypsum plaster was just coming into widespread use in the plastering trade. Interior plastering in the United States until the turn of the nineteenth century was generally carried out with lime plaster. Gypsum plaster sets quickly and allows for the application of additional plaster coats and finishing with paint within a short time frame. Gypsum plaster does not, however, have the same durability and water resistance as a true lime plaster. The contemporary accounts of the Ferris Grand finishing work mention that the “adamant” was employed; adamant was a trade name at the time for the new gypsum plaster.
In 1914 the state fire marshal ordered the Ferris Grand Opera House closed for reason of a number of safety concerns, including the need to replaster the ceiling. Plaster serves to protect the wood structure behind the finish from fire, it is an incombustible material, and so it would have been an important part of fire safety in a large auditorium building like the Ferris Grand. It is remarkable that the plaster ceiling, only 15 years old at the time, would have been in need of replacement. The poor condition of the ceiling must have been due to improper installation at the time of construction possibly resulting from rushed work, frost damage, or maybe from the plasterers’ unfamiliarity with a new type of material.