Manufacturing changes at the end of the 19th century made it possible to use gypsum as a plastering material.Gypsum and lime plasters were used in combination for the base and finish coats during the early part of the 20th century; gypsum was eventually favored because it set more rapidly and, initially, had a harder finish.Plastering is a skilled craft, requiring years of training and special tools.While minor repairs can be undertaken by building owners, most repairs will require the assistance of a plasterer.Plasterers in North America have relied on two materials to create their handiwork—lime and gypsum.Until the end of the 19th century, plasterers used lime plaster.Dry wall repairs are not included here, but have been written about extensively in other contexts.
From modest farmhouses to great buildings, regardless of the ethnic origins of the occupants, plaster has traditionally been used to finish interior walls.
First, three-coat plaster is unmatched in strength and durability. Of more concern to preservationists, however, original lime and gypsum plaster is part of the building's historic fabric—its smooth troweled or textured surfaces and subtle contours evoke the presence of America's earlier craftsmen.
Plaster can also serve as a plain surface for irreplaceable decorative finishes.
When building a house, plasterers traditionally mixed bags of quick lime with water to "hydrate" or "slake" the lime.
As the lime absorbed the water, heat was given off.
Not only did the basic plastering material change, but the method of application changed also.