Plaster- it’s types and application in the Construction Industry
Plaster and its History
Plaster is a building material used for coating, protecting and decorating internal walls and ceilings. It can also be used to create architectural mouldings such as ceiling roses, cornices, corbels, and so on.
A form of plastering was used by primitive civilisations, creating durable and weather-resistant structures using mud. The Egyptian pyramids contain plasterwork comparable to that used today that remains hard and durable some 4,000 years later.
Greek artisans used plaster, mainly to cover the exterior of temples but sometimes also interiors. Through history, plaster ceilings became increasingly ornamental, with those during the Tudor period being particularly extravagant.
Why do we need to plaster?
Plastering is the process of covering rough walls and uneven surfaces in the construction of houses and other structures with a plastic material, called plaster.
To improve the appearance of the surface by providing an even, smooth, regular, clean and finished surface.
In case of external plastering, the objective is to preserve and protect the surface from atmospheric influences by acting as a protective coating. In case of internal plastering, the basic object is to protect the surfaces against dust.
To conceal the defective workmanship and to cover up the use of inferior quality and porous material and joints formed in masonry work.
To provide a satisfactory base or ground for decorating the surface by applying white washing, painting, colour washing or dis-tempering.
To fill up the cracks detected in the structure during maintenance process.
Different Forms of Plaster
There are a number of different types of plaster, depending on the binder that is used.
Gypsum plaster, or ‘plaster of Paris’ (POP), is the most common form of plaster for interior walls. It is produced by heating gypsum to around 150°C (300 °F). When mixed with water, the dry plaster powder re-forms into gypsum. Unmodified plaster starts to set about 10 minutes after mixing, but it will not be fully set until 72 hours have elapsed. Gypsum plaster has good fire-resistant qualities.
Lime plaster is a composite of calcium hydroxide (lime) and sand (or other inert fillers). It may sometimes be strengthened with animal hair to preventing cracking and reduce shrinkage.
The plaster sets through contact with carbon dioxide in the atmosphere which transforms the calcium hydroxide into calcium carbonate (limestone). It is typically more flexible and breathable than gypsum and cement plasters, and is most commonly used on older properties.
Cement plaster is a mixture of sand, cement and water. It is normally applied to masonry interiors and exteriors. While it is capable of achieving a smooth surface, interiors will sometimes require an additional finishing layer of gypsum plaster. Cement plaster offers greater moisture resistance than gypsum plaster.
Clay plaster is considered to be a more sustainable alternative to modern plasters, with a lower embodied energy than gypsum, cement or lime-based plasters.
It is available with fibre additives to increase its strength, and in a range of ‘natural’ colours. It is breathable and does not need to be painted.
Mud plaster constitutes of Mud and Admixtures. The particles within mud are Clay (finest), Silt and Sand (coarse). In pure mud plaster, constituents of mud itself act as binder (clay in mud) and aggregate (sand in mud). In-case of clayey soil or sandy soil, clay content of mud is preferably kept between 12%-30%, by mixing mud types in required proportion. Fibres like rice husk is added to reduce cracks.
Cow Dung Plaster
Cow dung has traditional importance when it comes to plastering walls and floors. Cow dung is not only a good binder, but the fibres present in the dung also help in creating smooth, fine floor finish; the fibres prevent cracking in floors and also increases the insulation properties of the plaster.
The cow dung is an antifungal insecticide, which is why we have been confidently using them for disinfecting our homes and floors. It has antiseptic properties and it is also a prophylactic, meaning it prevents diseases. For fibres often cow hair is added to the plasters to prevent cracking.
Stucco is the common name for Portland Cement Plaster, which is applied either to the indoor or outdoor surfaces of buildings. Stucco is hard and durable. It’s also rots and fungus resistant. It’s a great low-cost home exterior material. It does not require a lot of maintenance.
Types of Plaster Finishes
The different type of plaster finishes are mentioned below:
1)Smooth Coat Finish: In this type of finish, the finishing coat is a smooth and levelled surface. The mortar used is made of cement and fine sand 1:3. Mortar is applied with the help of wooden float.
2)Sand Face Finish: Sand faced finish is applied in two coats. The first coat is applied in 1:4 cement sand mortar of 12 mm thickness. It is provided wish zig-zing lines. After curing it for seven days, the second coat is applied in the thickness 8 mm.The mortar for second coat is prepared from the cement sand mix ratio 1:1. The sand of uniform size is used. A sponge is used in a second coat when it is wet. he surfaces of final coat is finished by rubbing clean and washed sand of uniform size by means of wooden float. This results in the surface having sand grains of equal and uniform density.
3)Rough Cast Finish or Spatter Dash Finish: Cement, Sand and Aggregate are used to prepare mortar for this type of finish [1:1:3]. The coarse aggregate may vary from 3 mm to 12 mm in size.The mortar is thrown on the prepared plaster surface then by means of a large trowel. The surface is then roughly finished using a wooden float. This finish is water-proof, durable, and resistant to cracking and crazing. It is used for external rendering.
4)Peddle Dash or Day Dash Finish: In this finish, clean pebbles of size from 10 to 20 mm size are dashed against the final coat of plaster. The pebbles may be lightly pressed into the mortar with the help of wooden float. The final coat of plaster is having Cement: sand mix proportion of 1:3 and thickens 12 mm.
5)Depeter Finish: In this type of final finish coat of plaster is applied to have thickness 12 mm, and when it is a wet condition, the pieces of gravel flint are pressed with hand on the surface. Flints of different colours may be used to obtain beautiful patterns.
6)Scrapped Finish: The final coat of plaster of 6 to 12 mm applied. Then it is allowed to be stiffened for a few hours. The surface is scrapped in a pattern for a depth 3 mm. Steel straight edge old saw blades or such other tools may be used for scrapped. Such a scrapped surface is less liable to cracks.
7)Textured Finish: This is used with sketch plastering ornamental patterns or textured surface are made on the final coat of stucco plastering by working with suitable tools.
Two Most Popular plaster are
1) Neroo Plaster
2) Sand Faced Plaster.
Plaster for Home Décor
Plaster is also a very popular decor element in Arab history but probably reached its highest peak of popularity during the Renaissance. Plaster is a creative medium and creates unlimited varieties of Textures and surfaces which gives a stunning look to the exteriors of any building. Thus, we can conclude Plaster is the most important object when it comes for creating buildings.