![]() In recent decades, some home and building owners have removed the plaster from their brick walls to expose the brick surfaces. The plaster was usually applied in two coats (a brown coat and a finishing coat) over walls that were made of imperfect bricks and had mortar joints that were rougher or more tooled than the exterior walls. Plaster was typically applied to brick walls that were not intended to be exposed. Like the drywall used today, rock lath was nailed to the walls and ceilings and covered with two coats of lime- or gypsum-based plaster. Rock lath was a paper-faced, ½-inch-thick compressed gypsum board, generally 3 x 5 feet. The gypsum-based plaster also dried more quickly than the lime-based plaster.īeginning in the early 1900s and up to the 1960s, builders began to use rock lath in Wisconsin houses and buildings. The larger number of plaster-filled holes created better bonding keys. Metal lath did not contract and expand as much as wood lath, and the mesh screen had more holes for the scratch coat to ooze through. In the late 1800's, metal screen types of lath and gypsum-based plaster came into use because these materials had a few advantages. The third coat was a finer, 1/8-inch thick finishing layer. The second coat, called the brown coat, was a 3/8-inch-thick layer that created a flat surface on which to apply the final coat. Scratches were raked onto the plaster surface to create a bond for the second coat. The plaster oozed into the gaps between the lath strips to create plaster “keys” that held the plaster on the wall. The first coat, called the scratch coat, was a 3/8-inch-thick layer troweled onto the wood lath. The highest-quality plaster work was applied in three coats: A gap was left between each two adjacent wood lathes. After the mid-1850s, houses and buildings were constructed with thin, uniform strips of pine wood lath that were nailed to the interior stud walls and ceiling joists. The lime plaster was a mixture of lime, water and sand with animal hair used as a binder. Until about 1900, all plaster walls and ceilings were done with lime-based plaster applied over wooden lath. Be aware that if you remove the original plaster in your house or building as part of a rehabilitation project, you could jeopardize your eligibility for federal or state tax credits. Plaster is an important part of your house or building’s historic character. Plaster became popular because it is a durable, fire-resistant finish that muffles sound. The cured plaster can be painted or covered with wallpaper, stenciling or other decorative features. The plaster is allowed to dry or “cure” for a period of time. This paste is applied either to brick walls or over thin strips of wood lath in frame buildings and on ceilings. ![]() When mixed with water, plaster forms a thick paste. ![]() Plaster is a powder made primarily from lime or gypsum. It was the most common interior finishing material used during the 19 th and early 20 th centuries. Plaster has been used for thousands of years. If you own a historic house or commercial building, there is a good chance that your building has plaster walls and ceilings. Repaired plaster walls/ceiling - ready for paint. ![]()
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