Plastering is a process whereby a rough and hard surface is smoothened using application of layers of plaster mortar. Plastering can be done for purposes of painting a wall or ceiling, smoothening walls, or restorations. Different surfaces can be plastered. The type and consistency of mortar, however, will differ based on the surface you intend to work on. The number of layers of plastering also differs based on the surface you are working on. Here are three different types of plaster commonly used in the construction and restoration industry.
Cement plaster is probably the most recognizable plaster material used in the construction industry. Cement plaster is usually mixed with washed fine-grain sand and water to make the plastering mortar. The ratio of components varies based on the coat you intend to apply. If you are to use cement plaster as an undercoat, you would have to mix cement, and the sand at a ratio of one-part cement with three or four-parts washed sand. This is to level the hard background that is the wall before you apply the top coat of plaster.
For a second coat, cement plaster is usually used, but either a plasticizer or lime is included in the constitution. In this case, you can mix one-part cement with three-parts washed sand and a quarter-part of lime.
Lime plaster is commonly used when plastering for the restoration of old buildings. It is also very popular for a finishing coat. To make lime plaster, you mix washed sand with lime. The proportions are one-part sand and three-parts lime. This makes a softer mortar for plastering.
Because lime shrinks when it dries, several cracks may form on the surface after plastering. To avoid this, plasterers add animal hair to the mixture which holds the plastering together as it dries.
Gypsum plaster became widely popular to an extent that it has replaced both lime and cement plaster for various plastering uses. Depending on the mixture prepared, gypsum plastering can be used as an undercoat for the hard surface, and then again used for the second or third finishing layer. Gypsum's popularity is further fueled by the fact that instead of shrinking when drying, it slightly expands. This results in a consistency on the spread which is more favorable to work with.
Remember, the secret to good plastering is mixing the mortar to a smooth consistency — much like the feel of thick yoghurt — instead of a thick porridge-like mixture.