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Mar 14, 2024 · In medieval and Renaissance times, gesso (usually made of plaster of paris mixed with glue) was applied to wood panels, plaster, stone, or canvas to provide the ground for tempera and oil painting. Plaster of paris is prepared by heating calcium sulfate dihydrate , or gypsum , to 120–180 °C (248–356 °F).
- Gypsum Plaster
For especially hard finish plaster, the gypsum is completely...
- Fibreglass
Fibreglass, fibrous form of glass that is used principally...
- Gypsum Plaster
Feb 18, 2024 · Plaster of Paris, also known as gypsum plaster, has a rich history and a wide range of applications. It has been used for centuries as a casting material for sculpting and creating orthopedic casts. Its use in art and craft projects is also well-known.
Mar 2, 2017 · Named for the huge gypsum deposits of Montmartre, plaster of Paris’ appearance as a sculptural medium dates to Mesopotamia, when classical statues were draped in fringed gypsum skirts and dresses. From the Tigris and Euphrates the material made its way into Western European history through architectural details, columns, pilasters, and mouldings.
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May 6, 2014 · Plaster of Paris impressions were introduced around 1844–5. It is impossible to say who first used them, but credit is given equally to Amos Westcott, W.H. Dwinelle and E.J. Dunning. 11 , 12 Plaster impressions have always been coated with a separating media, such as a varnish or shellac, before a cast could be poured.
- 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...
For the purposes of this essay, ‘plasterwork’ will be taken to include both plaster and stucco work and will focus on the role internal decorative plasterwork played in the evolution of the Great House. Thus, this essay will not discuss the modern definition of ‘pargetting’ or other external uses of decorative plasterwork.
Print. Originally, the term ‘plaster of Paris’ was coined in the 1700s to describe plaster produced from gypsum located outside of Paris. Over time, the term ‘plaster of Paris’ has become the generic term for gypsum-based plaster. Many ancient Egyptian tomb paintings are created on plaster.
