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A Guide to Gypsum Plaster in Construction

It is a technique used to smooth and reinforce the rough surfaces of walls, columns, ceilings and other building components. Plaster not only provides aesthetic appeal, but also prevents surface deterioration from weathering and vegetation growth.

In geology, gypsum refers to a soft, sulfate mineral composition of calcium sulfate dihydrate. Rocks in which it is found are usually white in colour. Suitable proportions of gypsum powder and water are used to make gypsum plaster.

Gypsum Plaster History

The ancients plastered their shelters with mud to make them durable and stable. The use of gypsum and other materials began to replace mud with time. It is believed that plaster made of Gypsum was used as an internal plaster in the Giza Pyramid. The results indicate that gypsum plaster is durable and performs well.

Define Gypsum Plaster

Dry gypsum powder is mixed with water along with a small amount of accelerator to create anhydrous plaster. The setting time of gypsum plaster is reduced by using retarders like organic acids, soluble salts, basic phosphates, and proteins. The strength and non brittleness of gypsum plaster can also be improved with the addition of hardeners.

Preventive Measures of Gypsum Storing

As soon as gypsum is manufactured, it has a self-life of three to four months. It is possible to extend the self-life of a product for another six months if it is stored properly and with great care.

When exposed to humidity, moisture, or frozen backgrounds, the setting time for gypsum may be reduced. As a result, even in humid conditions, its hydrating property won't allow it to expire soon when stored in a closed area.

Gypsum Plaster Applying Process

Surface Preparation

With a wire brush, all masonry joints and surfaces are thoroughly cleaned. It should be confirmed that the surface is free of oil, grease, and other substances.

Gypsum Plaster Preparation

Powdered gypsum plaster comes in bags & is mixed with water and stirred for 2 to 3 minutes in a clean, dry vessel.

Gypsum Plaster Application

Firmly press the plaster onto the surface after it has been prepared. Continuing flattening Gypsum Plaster will keep it from stiffening. When the plaster has become sufficiently firm, clean the surface using sponge floats and water if necessary. The surface should be troweled progressively for a smooth finish.

Painting should not be allowed until the plaster has dried completely and not exposed to moisture. In addition to applying multiple coats of plaster, the thickness of this plaster should range from 6 to 20 mm.

Gypsum Plaster Thickness

The thickness of gypsum plaster is important when it comes to applying it to walls, ceilings, and other surfaces. Putting gypsum plaster on with a minimum thickness of 6 mm will prevent cracks and peeling.

It is recommended to apply gypsum plaster at a thickness of 6 to 20 mm. It is possible to apply an additional coat of cement sand plaster within an 8 to 12 mm thickness, and then coat it with gypsum plaster of at least 6 mm thickness for smooth finishing if the plastering thickness exceeds 20 mm.

There are a total of 25 kg of gypsum in each bag and each bag covers 21 square feet with a 12 mm thickness. You can paint the plaster after it has dried completely for aesthetic purposes.

Gypsum Plaster Features

Aside from being practically unaffected by bacteria, it is also light in weight. Plaster adheres well to fibrous materials and is slightly soluble in water.

Since it is set through natural crystallization, it can be applied easily without wasting resources. On drying, it shrinks very little and sets with little volume change.

Typically, the finishing coat can be applied the same day as the undercoat since it dries quickly. It is well known that porous gypsum is an excellent sound absorbing material, while dense and hard plasters are excellent sound reflectors. In addition to its high tensile and flexural strength, it has a low thermal conductivity, which helps it prevent corrosion.

Gypsum Plaster Types

Hemi-hydrate Gypsum Plaster

Heat Hemi-hydrates gypsum above 170 degree centigrade forms when hydrated gypsum is heated. An application prepared with Hemihydrates Gypsum plaster is known as Hemihydrates Gypsum Plaster.

Anhydrite Gypsum Plaster

The anhydrite gypsum is made by heating gypsum to 170 degrees Celsius. Gypsum plaster made from anhydrite is known as Anhydrite Gypsum Plaster.

Gypsum Plaster Merits

• Gypsum plaster can be used to obtain various decorative shapes.
• Plaster application is less time consuming, less expensive, and produces negligible waste.
• In addition to being easy to work with, it also provides an excellent finish.
• Time and water are directly saved as there is no need to cure.
• Because it has good binding properties, one coat of plaster is sufficient for plastering RCC ceilings, bare brick walls, and AAC blocks.
• Besides being eco friendly, it is unaffected by bacteria and prevents fungus growth.
• Many different textures and hardness’s of surfaces can be obtained easily & smoothen the surface of the product.
• Paint can be applied to gypsum plastered surfaces easily.
• Gypsum plaster can be controlled in its setting time by reducing the time gap between successive coats.
• Easily accessible and pre-mixed, it is one of the most popular materials.
• In addition to its white color, it also gives a beautiful appearance.

Gypsum Plaster Demerits

Exposed walls are susceptible to dampness, so it is unfavorable for them. It is undesirable in areas like bathrooms, kitchens, and toilets. The cost of cement and plaster for the same thickness is higher.

Gypsum Plaster Applications

• The material is used in high temperature ceilings and columns as a heat insulating material.
• Plasterwork with this material is ornamental.
• In ceilings, internal linings, and partition walls, gypsum plasterboards are used because they are cheap, lightweight, fireproof, and easy to work with.
• Its thermal insulation and low dead load make gypsum blocks very useful for construction of non load bearing partitions, which makes construction more efficient in dry conditions. As well as protecting columns, beams, and elevated shafts from fire, these blocks also serve as a fire retardant.
• It is possible to prepare slotted gypsum plaster tiles 13 mm thick and 300 mm wide using 65:35 parts of calcined gypsum and sawdust.
• Large offices and auditoriums use these acoustic tiles to reduce echo. Interconnected pores and the porosity of tiles determine the effectiveness of tiles.

To get more details, go through the following video tutorial.

Lecturer: Gyproc India

Gypsum Board

Gypsum boards have long, square edges, and their surfaces are made of gypsum with a paper surface. Wallboard can be referred to as drywall, plasterboard, or gypsum board.

False ceiling materials made of this material have a number of beneficial properties. Because of its thermal resistance, it keeps the room temperature constant. It is better to insulate sound with gypsum board than with concrete.

The material can be molded in a variety of shapes and patterns. A false ceiling made from gypsum boards can be fitted with LED lights which provide efficient lighting.

Aside from being fire resistant, it is also moisture free to a certain extent. A durable and economical option, it is also environmentally friendly.