![]() ![]() So, this isn’t like tapping a nail into soft, chalky drywall. A similar system, known as veneer plaster, is now used in some new construction. In those instances, gypsum plaster was applied to perforated gypsum board. There is another type of plaster wall that was occasionally used, starting in the mid-1930s, and that is known as rock lathe. Gypsum plaster is still being installed in high-end construction projects. The down side of gypsum is that it is somewhat more susceptible to water damage. Unlike lime, which could take many months to cure, gypsum begins to set up immediately and cures in a couple of weeks. In the 1920s, plasterers began using gypsum plaster. It was this coat, only about 1/8 inch thick, that created the beautiful, hard, smooth surface. The final coat, or finish coat, had a higher amount of lime and did not include animal hair. The first coat was known as the scratch coat and it was topped with a thinner layer, the brown coat, both adding up to about 3/8 of an inch. Applied in three coats, it was a mixture of quick lime, water, sand and animal hair. If your home was built up through the mid 1920s it is very likely that it was built with lime plaster. The keys are what give plaster its structural strength. If your home was built with traditional plaster walls, it has a system of wood strips, or lath, that were nailed across the studs with enough space between to allow the wet material to be forced through, creating an overhanging lip of plaster known as a key. The result may be cracked plaster and a hammer that almost seems to bounce off the nail, as the underlying wood lath repels the blow. Because of the hardness and multi-layered construction of a plaster wall, it is not easy to pound in a nail. Many homeowners’ first experience with the unique properties of plaster is while trying to hang a picture. In addition, replacing plaster with standard drywall has the effect of reducing the historic integrity of the building and, therefore, impacts the monetary value of the home within the historic home market. The transmission of voices, footsteps, music and plumbing sounds is particularly annoying. The alternative, modern drywall, has a flat cardboard-like appearance and lacks the sound-insulating quality and fire resistance of plaster. Worse yet, these materials greatly increase the chance for damaging moisture build-up and harmful mold growth, as well as, trapping the toxic fumes from out-gassing paint finishes and petroleum-based furnishings.Īlthough the environmental concerns are significant, it is the rich, textural beauty of plaster that is its greatest asset and the most compelling reason to preserve and restore this valuable material. Unfortunately, well-intentioned improvements, like blown-in insulation, vinyl replacement siding and vapor barriers actually defeat the old, efficient system of moisture exchange and add little to improve on the insulating air pocket between the plaster lath and the exterior walls. The most efficient and economical solution to cold air leaks is to maintain and replace caulk around windows and along all gaps and cracks. The chilly interior drafts that you feel each winter are pouring through joints, cracks and crevices and are not coming through the walls themselves. ![]() In fact, plaster and wood are very poor conductors. While humidity passes through the materials to the outdoors, heat and cold are not transferred. Homes built of wood and plaster are actually a superb, natural-functioning system. Yet plaster is the first element that a contractor will tell you “has to go.” Actually, more often than not, it will be removed because either the contractor does not have the knowledge necessary to make repairs and/or the homeowner does not realize what will be lost along with its removal. ![]() Have you ever run your hand along the wall of an old house on a hot summer day and been surprised by its coolness? Flat plaster walls that were installed in homes until as late as the 1950s are an integral part of both the historic and environmental value of older homes. ![]()
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