🕑 Reading time: 1 minutePlastering is a process by which coarse surfaces of wall or ceiling roofs are changed or turned or rendered to provide smoothness. At the beginning, wet materials are spread over the block or brick works and then suitable equipment is used to make the surface smooth level. The prime purpose of plastering is to obtain hard and smooth surface that could be painted and provide nice aesthetic appearances. Recently, wall surfaces in modern houses are finished with bricks or blocks or aesthetically pleasing stones to show beautiful appearances. Wet materials that spread over wall or roof surfaces should not be more than 0.3 cm. However, there are surfaces that irregularities are more than 3cm. In this case under coat which is low cost coarse grain material is used to render the surface followed by finish coat that is thin layer of fine grain materials. Moreover, walls constructed from irregular and different size stones might require three coating. This is because thick under coat tend to sag due to weight of thick wet plaster. That is why spreading thin layer and permitting to harden followed by employing second under coat is the best practice as shown in Figure 1. Finally, finish coat is applied for the surface.
Figure-1: Advantages of Two Under Coat of Plaster
- Types of Plaster based on Material Used
- Background Surfaces for Plaster
- Plaster Finishes to Timber Joists and Studs
- Skirting and Architraves
- Types of Plaster Finishes used in Building Construction are:
- External Rendering of Buildings
Types of Plaster based on Material Used
Lime PlasterLime mixture consists of sand and line that are mixed by 1 sand to 3 of lime by volume. Not only this mixture is used for under coat but also used as finish coat. Lime plaster might be shrink after drying so animal hair of about 5 Kg is used for 1 m2 to avoid lime plaster cracking and shrinking. Lime plaster could be used for ancient structure restoration and rehabilitation.
Cement PlasterGrey powder Portland cement is mixed with water by the ratio of 1cement to 3 or 4 clean washed sand by volume as an under coat for hard background for example brick block walls and partitions. Mixture of sand and cement might be plastic and require experienced and skill labor therefore plasticizer or lime is added to the mixture usually by volume ratio of 1cement:0.25 lime: 3 sand or 1 cement to 4 sand with plasticizer. Plasticizer is a liquid that added to the mixture to ease plaster spreading over the surface.
Gypsum PlasterGypsum plaster is widely used plaster materials that could be mined naturally or produced as a by-product. So, important gypsum plaster that is employed as under coat, finish coat, and replaced lime and cement broadly. Moreover, small expansion of gypsum is considered significant propertied that prevent shrinkages and cracks. There are various types of gypsum plaster that are produced by heating gypsum to a specific degree for example anhydrous gypsum manufactured by heating gypsum up to 170 Co, hemihydrates gypsum produced by heating gypsum more than 170 Co. Furthermore, depending on applications for walls or ceilings gypsum plasters can be categorized such as casting, undercoat, finish, one coat and machine applied plaster.
Background Surfaces for PlasterType of plaster and its application varies depending on the surface of the wall or ceiling which are set to be plastered. Bricks or blocks with rough and solid surfaces possess means of mechanical adhesion when plaster is applied to the background walls or ceilings. The mechanical keys which adhere hardened plaster to the surfaces is created after spread wet undercoat plaster is dried. Plaster keys limit or restrain shrinkage of the cement that is principal component of undercoat plaster. Machine pressed bricks with high density and smooth surfaces absorb suitable amount of water that will help adhering plasters to surfaces. The degree of water absorption by dense smooth surface bricks which assist in plaster adhesion is called suction. Blocks produced by light weight concrete have large suctions that prevent attaching plasters to surfaces properly. Therefore, it is advised to decrease water absorption degree by either liquid primer or spraying water before plastering. There are two different solutions for surfaces with low suction include PVA bonding agent and polymer bonding agent. In the former method, polyvinyl acetate is brushed on the surface and plaster is spread over when the PVA is still sticky which creates bond. In the latter, surfaces are treated by combination of silica sand and polymer and the bond is provided by silica sand grain after the polymer is dried. There are various types of galvanized steel beads and stops which are produced to employ with plaster and plasterboard as angle and stop reinforcement. The beads are used at the junction of wall to ceiling plaster and plaster to other materials. Galvanized steel utilized as stops to create perfect finishes at junctions of plaster to another material at angles, around windows and doors, and skirting as shown in Figure 2.
Figure-2: Metallic Beads and Stop for Plasters
Plaster Finishes to Timber Joists and StudsPlaster spreading on timber lath is an old and traditional technique that used to create level finished surface to the timber floor ceiling and roofs and stud partitions. This method to a large degree replaced by gypsum plasterboard that is why further detailing is not provided. Gypsum plasterboard is made of hard gypsum plaster that bonded to two heavy papers which prevent damages resulted from handling and installing of the gypsum plaster. It is manufactured with various thicknesses for example 0.95 cm, 1.25 cm, 1.5 cm. and 1.9 cm that applied as dry lining or as plaster background in different size boards. Gypsum plaster board is widely utilized in ceilings of timber floors and roofs as linings. Plasterboard is considerably cost effective and could be installed and plastered easily. Another outstanding advantage is resistant to fire because it is incombustible. Nonetheless, poor sound insulation and movement or vibration cracks are drawbacks of plaster boards.
Skirting and ArchitravesSkirts are narrow band made around wall base at wall and floor intersection and manufactured strong enough to resist hits. It serves to emphasize wall and floor junction. There are various types of skirting such as timber, metal, tile, and magnesite. Architraves are mold or forms which are used for decorative purposes installed around doors and windows.
Types of Plaster Finishes used in Building Construction are:Different types of plaster finishes with different appearances are available as follows.
- Smooth cast finish
- Rough cast finish
- Sand faced finish
- Pebble dash finish
- Scrapped finish
- Depeter finish
- Textured finish