Plastering is one of the most common and ancient finishing techniques. Plastering is applied to give a visually pleasing smooth surface to block or brick masonry of the wall. Plastering not only enhances beauty but also acts as a protective cover for bricks and stones and protects them from rain and wind.
Depending upon desired finishes, ingredients, popularity & required proportion, different types of plasters are used in different works. Different plasters available in the market are cement plaster, clay plaster, mud plaster, gypsum plaster, etc.
In the past few decades, gypsum plaster has gained popularity and has largely replaced lime and cement plasters. Here, we are going to discuss the properties, method of application, advantages, and disadvantages of gypsum plaster.
History of Gypsum Plaster
Gypsum plaster is not a recent invention. It is in use for centuries in the construction field due to its excellent properties. Gypsum plaster was used by the ancient Egyptians to plaster the pyramid at Cheops. The usage of gypsum plaster as an internal plaster in the pyramid of Giza of Egypt is proof of its performance and durability.
What is Gypsum Plaster?
In gypsum plaster, gypsum is used as a binding material instead of cement. It is a white cementing material made by partial or complete dehydration of the mineral gypsum. When dry gypsum powder is mixed with water it becomes hard. It is available in ready to use format and doesn’t need sand. Only the addition of water is required. It offers excellent acoustic and thermal properties while giving leveled walls with the best finish.
Gypsum plaster provides a smooth interior finish and is an ideal base for good quality wallpaper finishes and paints. It can be applied on both rough and smooth surfaces of the wall. Gypsum plaster is easy to apply and requires less skilled manpower, compared to the traditional cement mortar. The surface preparation and application of gypsum plaster should be apt to prevent cracks and peel offs.
Gypsum plaster can be applied directly on bricks, hollow or solid blocks, AAC blocks, and plasterboards. Gypsum plaster has good insulation properties, impact-resistant, and fire-resistant. Also, gypsum saves a lot of time during construction and has a superior finish. These properties have clearly drawn the attention of real estate builders and contractors towards choosing gypsum plaster over traditional cement plaster.
Technical Specification of Gypsum Plaster
Color of Finished Surface: White
Setting Time: 25-30 Minutes
Coverage Area: 21 Sq.ft per 25 kg Bag
Compressive Strength: 60-70 kg/cm2
Storage of Gypsum at Site
- The surface exposed to moisture reduces the setting time and strength of gypsum plaster. So, Gypsum bags have to be stored on elevated surface (dry platform) made of brick/timber/concrete at site.
- The minimum shelf life of gypsum plasters 3 to 4 months from the date of manufacture. But if properly stored gypsum can be use in excessive of 6 months subjected to temperature and humidity.
Method of Application
After surface preparation, gypsum plaster is applied in the following manner.
- Gypsum plaster generally comes in ready-mix bags. Extract the powder in a clean dry vessel, add water stir the mixture for 2 to 3 minutes.
- Ensure the thickness of plaster needed is not more than 13 mm.
- Apply gypsum plaster to the surface with firm pressure.
- As the plaster stiffens, carry out further flattening. When the plaster is sufficiently firm, scour the surface with sponge float and water as per requirement.
- Trowel the surface progressively to get a smooth finish.
- The plastered surface should be protected from continuous exposure to moisture.
- Painting work should be started only after the surface has become completely dry.
Advantages of Gypsum Plaster
- No shrinkage cracks: The gypsum reaction produces less heat as compared to the cement reaction with water. So there are fewer shrinkage cracks in gypsum plaster as compared to traditional cement mortar plaster.
- High Performance: Excellent high performance after drying. Durable and lightweight.
- Saves construction time: Gypsumplastering does not have this long waiting period. Gypsum plaster dries & settles in 3 days, and hence the construction pace is faster. The construction time is saved manifold if the building is multistory. In traditional cement mortar plaster, one would have to wait for 21 days for each floor, whereas it will be just 3 days in the case of gypsum plastering. Gypsum plaster saves a lot of construction time.
- Curing not required: Gypsum plaster does not need any curing saving water and time during construction.
- Fire Resistant: Gypsum is fire-resistant, non-combustible since it has a lot of water in it, and safe material to coat the inside walls of your home.
- Ease of Application: Gypsum can be directly applied over brick/blockwork without separate finishing. Gypsum plaster is very easy to apply and level.
- High Productivity: Reduces time considerably when compared to conventional cement mortar plaster.
- Smooth Finish: Perfectly lined leveled, smooth walls, and perfect right-angled corners.
- Reduced Supervision: Careful quality checking is required for cement mortar plaster as cement and sand has to be properly proportioned. In contrast, gypsum plaster does not require the same amount of quality checks for application thus reducing supervision efforts.
- Readily Available Raw Materials: Gypsum is a readily available material. Natural sand, which is a raw material used in traditional cement mortar plaster, is hard to obtain. Natural sand or river sand is also banned in many countries.
- Fire Resistant: Gypsum plaster is highly fire-resistant.
- Low Thermal Conductivity: Gypsum plaster has low thermal conductivity. This saves electrical costs for heating and cooling rooms in a building.
- Decorative Application: Gypsum plaster can be easily applied to decorative purposes also and can be mould into different shapes.
- Quick Setting Time: Gypsum sets normally setting 25 to 30 minutes. So painting could be started 72 hours after the application o gypsum plaster. The plaster has to be dried up before painting.
- Lighter Construction: Gypsum is very light in weight in contrast to sand cement plaster, and thus offers more strength when used in false ceiling and other cantilever designs. Lesser weight on the frames makes them more robust and long-lasting and gives better protection even in case of natural hazards like earthquakes.
Disadvantages of Gypsum Plaster
- Gypsum plaster can’t be used for outside walls since they retain dampness. Also, gypsum plastering can’t be done in areas that are continuously damp such as the bathroom, toilet, wash area, etc.
- Gypsum plaster is not recommended for use in areas subjected to the weather, moisture, or high humidity.
- Gypsum plaster is costlier than traditional cement mortar for the same thickness of plaster. But in areas where natural sand or river sand is not available for construction, cement mortar plastering would require a 6 mm gypsum layer to finish it making cement plaster more costly