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Questions and Answers
What is the term used to refer to gypsum plaster?
What is the term used to refer to gypsum plaster?
What is added to the plaster mixture to give increased strength for the first coat?
What is added to the plaster mixture to give increased strength for the first coat?
What are the three coats of a three-coat plastering job?
What are the three coats of a three-coat plastering job?
What is the main difference between two-coat and three-coat plastering?
What is the main difference between two-coat and three-coat plastering?
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What is the primary ingredient in lime plaster?
What is the primary ingredient in lime plaster?
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Which masonry unit is referred to as a 'DURISOL' block?
Which masonry unit is referred to as a 'DURISOL' block?
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What temperature is Plaster of Paris mixed with alum or borax burned at?
What temperature is Plaster of Paris mixed with alum or borax burned at?
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Which type of plaster is used for ornamental plaster work and castings?
Which type of plaster is used for ornamental plaster work and castings?
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What is the thickness of the scratch and brown coats in three-coat plastering work?
What is the thickness of the scratch and brown coats in three-coat plastering work?
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What is the type of plaster that is used for interior use only?
What is the type of plaster that is used for interior use only?
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Which material is not included in the mix for sand float finish?
Which material is not included in the mix for sand float finish?
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What determines the thickness of plaster coats in application?
What determines the thickness of plaster coats in application?
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What is the primary use of gypsum plaster according to the text?
What is the primary use of gypsum plaster according to the text?
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What is a key characteristic of lightweight gypsum plaster mentioned in the text?
What is a key characteristic of lightweight gypsum plaster mentioned in the text?
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What is a key use of Keene's cement?
What is a key use of Keene's cement?
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What type of masonry unit is a 'Plaster Block' according to the text?
What type of masonry unit is a 'Plaster Block' according to the text?
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What is the primary purpose of 'Durisol Block' according to the text?
What is the primary purpose of 'Durisol Block' according to the text?
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Which of the following is not a type of plaster mentioned in the text?
Which of the following is not a type of plaster mentioned in the text?
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Study Notes
Types of Plaster and Their Uses
- Gypsum plaster is used for interior finish for smooth concrete walls or ceilings, mixed with ingredients that develop more adhesive strength.
- Lightweight gypsum plaster is used when weight is important, and for fire-proofing other materials such as steel.
- Gypsum plaster is mixed on the job with water, perlite, vermiculite, or other suitable mineral aggregate.
- Gypsum plaster is applied on lath and is for interior use only.
Gypsum Plaster
- Bonding plaster is a type of gypsum plaster used for interior finish.
- The words "gypsum" and "plaster" are often used interchangeably.
- Fiber or hair is sometimes added to the mixture to give increased strength.
Plastering Methods
- Plastering is done according to two basic methods: two-coat and three-coat.
- A three-coat job consists of: a first binding coat called scratch coat, a second straightening coat called the brown-coat, and a final coat called the finish coat.
- In the two-coat work, the scratch and brown coats are combined into one.
Lime Plaster
- Lime plaster is mixed on the job with sand and gypsum plaster.
- Lime putty (hydrated lime and water) is used for two and three-coat finish surfaces for interior walls and ceilings.
- The ratio of lime putty to Po land cement or Keene's cement to sand by weight is:
- Scratch coat: 1 part lime putty, 1 part Po land cement or Keene's cement, 2-3/4 parts sand.
- Brown coat: 1 part lime putty, 1 part Po land cement or Keene's cement, 3 parts sand.
- Finish coat:
- Hard finish: 1 part lime putty, 1/3 part gypsum plaster by volume.
- Sand finish: 1 part lime putty, 1/4 part gypsum plaster, 2 parts sand by volume.
Other Types of Plaster
- Plaster of Paris is mixed with alum or borax or other materials and burned (calcined) at 932°F.
- Plaster of Paris is used for ornamental plaster work and castings.
- Molding plaster is used for ornamental plaster work and castings.
- Acoustics plaster is used for acoustic treatment of interior walls and ceilings, applied on gypsum plaster base coats.
Po land Cement Plaster
- Po land cement plaster is mixed with water, sand, and lime putty.
- It is used for two and three-coat finish surfaces for exterior and interior walls and ceilings.
- The ratio of cement to lime putty to sand is:
- Scratch and brown coats: 1 part cement, 1/4 part lime putty, 3 parts sand.
- Sand finish: 1 part cement, 1/4 part lime putty, 3 parts sand.
- The thickness of plaster coats depends on the type of material to which the plaster is applied.
- Generally, the total thickness is 5/8" on metal lath and 1/2" on lathing board and gypsum block.
- In three-coat plastering work, the scratch and brown coats are 1/4" thick at minimum; the finish coat is 1/8" with a minimum of 1/16" at any point.
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Description
Test your knowledge on the different applications of Plaster of Paris in construction and design, such as ornamental plaster work, castings, acoustic treatments, and more. Learn about mixing techniques, temperature requirements, and specific uses for interior finishes.
