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Plaster’s rich contribution to the beauty and protection of the surface of walls hardly needs arguing. The most popular types of plaster that are used for building construction are cement and gypsum plaster. These plasters are used for external and internal plastering of the building; they form a protective layer that covers stone and brick masonry along with the RCC walls and ceilings. Additionally, wall plastering is effective in levelling the wall and ceiling surfaces; gypsum and cement are also used for creating textured or stucco plaster and finishes.

Cement plaster
Cement plaster is a homogeneous mixture composed of Portland cement, sand and water. The cement plaster thickness usually ranges between 12 and 20 millimetres, depending on the type of wall or ceiling surface that needs to be plastered.

Pros

• Cement plaster can be used for plastering both the external walls and the internal walls and ceilings of the building.
• The external cement plaster on the building facade is the first line of defence for the building from wind, rain, and harmful industrial gases and vehicular pollution.
• Unlike gypsum plaster, cement plaster is resistant to moisture.

Cons

• The final finish of cement plaster is very rough and grey in colour. Hence, the walls have to be treated with POP punning (plaster of Paris punning) to achieve a smooth finish before the application of wall paint. Punning is the application of thin layers of plaster or mortar on a wall to achieve a smooth and flat finish.
• Cement plaster has the tendency to shrink, which results in hairline cracks on the plastered surface.
• The cement-plastered surface needs curing (a chemical reaction that achieves strength) with water for at least seven days. Do note that improperly cured walls develop cracks.
• Cement plaster is prone to attacks by mould or mildew.

Gypsum plaster
Gypsum plaster is factory-made. Unlike cement plaster, it is white. It is available in powdered form and is mixed with water to form a ready paste that can be directly applied to the wall and ceiling surfaces at site. The approximate thickness of gypsum plaster is 11 millimetres for walls and 8 millimetres for the ceiling. Gypsum plaster is also used to fabricate ceiling cornices and mouldings.

Pros

• Gypsum plaster gives the walls and ceilings a smooth, level surface that is ready to receive paint. Hence, it reduces POP punning costs which have to be incurred for cement plastered surfaces.
• The gypsum plaster paste is very easy to work with and prepare, in comparison to cement plaster.
• Gypsum plaster is highly resistant to mould and mildew.
• Gypsum plaster does not shrink as it undergoes very little expansion and contraction.
• Gypsum is a green product because it can be recycled an infinite number of times. Made from natural gypsum rock, it is dehydrated to produce a plaster powder. Adding water produces gypsum plaster. This plaster can be salvaged and again converted to powder plaster for re-use.
• The biggest advantage of going with gypsum plaster is that it dries very fast – within a span of 24 hours. However, the wall or ceiling surface should be painted only 72 hours after application.
• Due to gypsum’s low thermal conductivity, it keeps your house warm during the cold months and cool during the warm summer.
• Gypsum plaster has great resistance to fire.

Cons:

• The disadvantage of gypsum plaster is that it can only be used in the interiors of the building; it is not suitable for external plastering.
• Gypsum plaster should not be used in moisture-laden areas like the bathrooms, kitchens, balconies or damp basements.

Gypsum is a superior finish compared to cement plaster. However, it is advisable to go with gypsum plaster for the internal walls and ceilings and use cement plaster for the exteriors of the building.