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plaster of paris, quick-setting gypsum plaster consisting of a fine white powder (calcium sulfate hemihydrate), which hardens when moistened and allowed to dry. Known since ancient times, plaster of paris is so called because of its preparation from the abundant gypsum found near Paris.
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- Gypsum Plaster
Feb 18, 2024 · Plaster of Paris has its origins in the Paris Basin, where large deposits of gypsum were found. The production of plaster of Paris involves a process called calcination, where the gypsum is heated to remove the water content and create calcium sulfate hemihydrate.
- Gypsum Plaster
- Common Plaster Problems
- Structural Problems
- Poor Workmanship
- Moisture
- Repairing Historic Plaster
- Canvassing Uneven Wall Surfaces
- Filling Cracks
- Establishing New Plaster Keys
- Replastering Over the Old Ceiling
- When Damaged Plaster Cannot be Repaired-Replacement Options
- Replastering-Alternative Lath Systems for New Plaster
- Painting New Plaster
- Summary
- Plaster 1enns
Gypsum begins to cure as soon as it is mixed with water. It sets in minutes and completely dries in two to three weeks. Historically, gypsum made a more rigid plaster and did not require a fibrous binder. However, it is difficult to tell the difference between lime and gypsum plaster once the plaster has cured. Despite these desirable working chara...
When plaster dries, it is a relatively rigid material which should last almost indefinitely. However, there are conditions that cause plaster to crack, effloresce, separate, or become detached from its lath framework (Fig. 7). These include: Structural Problems Poor Workmanship Improper Curing Moisture
Overloading. Stresses within a wall, or acting on the house as a whole, can create stress cracks. Appearing as diagonal lines in a wall, stress cracks usually start at a door or window frame, but they can appear any where in the wall, with seemingly random starting points. Fig. 7 (a) to (d). series of photographs taken in different rooms of an earl...
In addition to problems caused by movement or weak ness in the structural framework, plaster durability can be affected by poor materials or workmanship. Poorly proportioned mix. The proper proportioning and mixing of materials are vital to the quality of the plaster job. A bad mix can cause problems that appear years later in a plaster wall. Until...
Plaster applied to a masonry wall is vulnerable to water damage if the wall is constantly wet. When salts from the masonry substrate come in contact with water, they migrate to the surface of the plaster, appearing as dry bubbles or efflorescence. The source of the moisture must be eliminated before replastering the damaged area. Sources of Water D...
Many of the problems described above may not be easy to remedy. If major structural problems are found to be the source of the plaster problem, the structural prob lem should be corrected. Some repairs can be made by removing only small sections of plaster to gain access. Minor structural problems that will not endanger the building can generally b...
Uneven wall surfaces, caused by previous patching or by partial wallpaper removal, are common in old houses. As long as the plaster is generally sound, cos metically unattractive plaster walls can be "wallpa pered" with strips of a canvas or fabric-like material. Historically, canvassing covered imperfections in the plaster and provided a stable ba...
Hairline cracks in wall and ceiling plaster are not a serious cause for concern as long as the underlying plaster is in good condition. They may be filled easily with a patching material (see Patching Materials, page 13 ). For cracks that re-open with seasonal humidity change, a slightly different method is used. First the crack is widened slightly...
If the back of the ceiling lath is accessible (usually from the attic or after removing floor boards), small areas of bowed-out plaster can be pushed back against the lath. A padded piece of plywood and braces are used to secure the loose plaster. After dampening the old lath and coating the damaged area with a bonding agent, a fairly liquid plaste...
If a historic ceiling is too cracked to patch or is sagging (but not damaged from moisture), plasterers routinely keep the old ceiling and simply relath and replaster over it. This repair technique can be used if lowering the ceiling slightly does not affect other ornamental features. The existing ceiling is covered with 1x3-inch wood furring strip...
Partial or complete removal may be necessary if plaster is badly damaged, particularly if the damage was caused by long-term moisture problems. Workers un dertaking demolition should wear OSHA-approved masks because the plaster dust that flies into the air may contain decades of coal soot. Lead, from lead based paint, is another danger. Long-sleeve...
Replastering old wood lath. When plasterers work with old lath, each lath strip is re-nailed and the chunks of old plaster are cleaned out. Because the old lath is dry, it must be thoroughly soaked before applying the base coats of plaster, or it will warp and buckle; further more, because the water is drawn out, the plaster will fail to set proper...
The key to a successful paint job is proper drying of the plaster. Historically, lime plasters were allowed to cure for at least a year before the walls were painted or papered. With modern ventilation, plaster cures in a shorter time; however, fresh gypsum plaster with a lime finish coat should still be perfectly dry before paint is applied-or the...
The NationalPark Service recommends retaining his tone plaster if at all possible. Plaster is a significant part of the "fabric" of the building.Much of the building's history 1s documented in the layers of paint and paper found covering old plaster. For buildings with decora tive painting, conservation of historic flat plaster is even more importa...
Scratch coat. The first base coat put on wood or metal lath. The wet plaster is "scratched" with a scarifier or comb to provide a rough surface so the next layer of base coat will stick to it. Brown coat. The brown coat is the second application of wet, base-coat plaster with wood lath or metal systems. With gypsum board lath (rock lath, plasterboa...
History. Plaster was first used as a building material and for decoration in the Middle East at least 7,000 years ago. In Egypt, gypsum was burned in open fires, crushed into powder, and mixed with water to create plaster, used as a mortar between the blocks of pyramids and to provide a smooth facing for places.
We explore the process of mining the stone, crushing it into a fine powder, and transforming it into Plaster of Paris. With our step-by-step guide, you'll gain a deeper understanding of how...
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The production of plaster casts or other plaster wares begins with a dry, fine white powder, produced by heating the mineral compound gypsum. Gypsum plaster, as distinct from lime plaster (more commonly used in fresco and whitewash, for example), is also named Plaster of Paris for the large deposits of the material in Paris near Montmartre.
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Oct 16, 2013 · 1. History. The name Plaster of Paris (POP) had its origins from the fact that it was extensively mined from Montmartre in Paris district. But its use predates the industrial revolution, they have been found on the insides of pyramids.
