Plastering is a method in which coarse and rough surfaces of walls and ceilings are leveled out using different kinds of materials to achieve smooth surface. The process basically involves spreading wet plastering materials over blocks or bricks and using proper tools smoothen out the surface. The main purpose of plastering bricks and blocks is to achieve a smooth surface in which building contractors can easily paint the wall or ceiling facade with different colors and shades.
Aside from flat and smooth plaster surfaces, there are also other finishes that you can choose from such rough cast, sand faced, pebble dash and textured. Different materials are needed in order to achieve these finishes.
As a general rule of thumb, wet plastering material that are evenly spread over walls and ceiling should not exceed more 0.3 cm in thickness. This is the most ideal thickness of the material without compromising the quality of the plaster and also as a cost-saving measure. There are however exceptions to this rule such as surfaces that have visible irregularities that is more than 0.3 cm. To fix this, use low-cost coarse plastering material as undercoat followed by fine-grain finish coating material. Having two coats of different material is not only cheap but it is also an effective method of concealing abnormalities on the wall and ceiling surface. Additionally, walls that are constructed using different and irregularly-shaped stones and bricks might require up to three layers of plaster in order to flatten out to desired thickness.
Types of Plaster
Lime plaster or lime mortar mixture basically consists of 1-part sand and 3-parts lime that is mixed by volume. This plaster can be both used as an undercoat and also as a finishing coat. This material has been used for centuries on old house because of its durability. Lime plaster will not soften and dissolve if contaminated by water for a long time. Unlike traditional cement plaster, lime plaster is less brittle and will not easily succumb to cracking. The high pH level of lime also acts as a natural fungicide making the wall resistant to molds.
Sand cement plaster is made up of 1-part cement and 3-part sand by volume to achieve the desired quality. It is used as an undercoat for hard walls such as bricks and partitions. Plasticizers are mixed to the plaster in order to ease the spreading of the mixture over any surfaces. It can also help in preventing bugs and parasites from penetrating the wall.
The most popular type of plaster that is extensively used today is the gypsum plaster. It is a versatile and flexible material that can be used as both an undercoat and topcoat and is a good alternative to lime and cement plaster. Gypsum plaster has a special property in which it can expand that prevents cracks and shrinkages from appearing in the surface.
Smooth cast finish
In achieving smooth cast plaster finish, the mortar must have a ratio of 1-part cement and 3-part sand per volume. Fine sand should be used in the plaster mixture to ensure a smooth surface. Use skimming or wood float in spreading the mortar to obtain a leveled surface.
Rough cast finish
Also called spatter dash finish, rough cast finish is a mixture of coarse aggregate, cement and sand. The ration of the plaster is about 1:1.5:3 per volume and the size of the aggregate is around 3mm to 12mm. Wooden float is used in leveling the plaster over the wall and ceiling surfaces. This type of finish is best used in external applications due to its rough nature.
Sand faced finish
This type of plaster finish requires two coats of plastering; the first coat should have 12mm thick cement sand mortar and allowed to be cured for 7 days. After the curing stage, a second layer of cement and sand coat is applied and level the surface using sponge and wooden float. The sand must be of uniform grain size in order to achieve a consistent surface.
Pebble dash finish
A mortar layer of about 12mm thickness is required in achieving pebble dash plaster finish. The ratio of the cement and sand is about 1:3 per volume. After plastering, pebbles of the same size and shapes are slowly dashed on the plaster surface using wooden float. This will ensure that each pebble are dashed equally and uniformly on the plaster surface.