The process of applying a coating or covering to obtain smooth and even texture for ceilings, walls, and other surfaces is known as plastering. The thin layer of coating that is used in this process is called plaster. Cement plastering plays a vital role in protecting the buildings. The different types of plasters and the importance of the plastering process are explored here.
List of Contents
1. Objectives of Plastering
The main objectives of plastering are as follows:-
Protection of the surfaces exposed to weathering and other effects of atmospheric agents.
For decorative purposes. For instance, plastering of ceilings and walls can be in such a way that it can incorporate designs and textures.
To conceal the low-grade material used as well as the poor quality workmanship in construction.
2. Points to Remember While Plastering
The sand to be used for plastering should be sharp, angular, and free from dust and other impurities.
The aggregates should be washed properly to ensure that there is no more than 5% of clay present in the sand. The clay tends to prevent the cement or lime from binding together with the sand particles.
The aggregates and the binder should be thoroughly mixed to obtain the desired consistency. The plaster ratio must be followed correctly.
The amount of water in the mortar should be monitored carefully to ensure that crazing does not occur on the plastered surfaces.
The plaster should not be made to dry quickly as it will lead to crazing, which spoils the plastering done.
The water and aggregates used should be void of all kinds of salts and impurities. The presence of soluble salts in the mixture; will lead to salt crystallization and the plastered surface will start to crumble or powder.
The projections extending beyond 13 mm from the general surface of the masonry should be knocked off so as to maintain a thinner layer of plaster. This will reduce the amount of plaster mortar used.
All the joints in the masonry face should be raked out for a depth of about 16 or 20 mm. These joints should be cleaned from all loose dust and mortar. This is very essential to obtain a good texture for the plaster; otherwise, separation from backing or in between coats will occur.
The thickness of a single coat should not be more than 15 mm.
The wall surface should be made wet prior to plastering. The dry back will suck water from the mortar and proper adhesion will not take place.
The plaster shall be laid over the full length of the wall or till the height of doors or windows.
3. Methods of Plastering
Some of the methods that can be followed in lime plastering or cement plastering are:-
Lime Plaster can be applied in many ways:
Three Coat Plastering
Two Coat Plastering
2. Cement Plaster and Cement-Lime Plaster is applied in:
Two-coat plaster
Three coat plaster
Single coat plaster
3. Plaster on Lath
Laths are done to provide a stable foundation for plasterwork and they are of two types:
Wooden laths
Metal laths
4. Types of Plastering
The main types of plastering available are:-
Lime Plaster
Stucco Plastering
Waterproof Plaster
Composite Plaster
Special Plaster
5. Types of Plaster Finishes
There are different types of plaster finishes available in the market today. Some of them are:-
Smooth-Cast Plaster Finish
Rough Cast Plaster Finish
Sand Faced Plaster Finish
Pebble Dash Plaster Finish
Depeter Plaster Finish
Textured Plaster Finish
6. Defects in Plastering
An impervious layer of plaster works well if it is mixed in the right ratio. Movements in the structure usually cause cracks, through which rainwater can penetrate. The moisture that has penetrated inside the plastering accumulates causing the structure to become damp and weak. The impervious nature of the plaster further restricts the backward flow of water. Thus the accumulated water inside the walls has no escape. The prolonged presence of water in walls questions the structural integrity of the buildings. The methods of plastering should be followed correctly in order to bring out the best results.
7. Crazing
The presence of fine hairline cracks in an irregular pattern on plastered walls or ceilings is called crazing.
The reasons for crazing are listed below:
The plaster surface was allowed to dry quicker than usual due to continuous exposure to sunlight.
It may be due to the application of the plaster finish before setting of the backing.
Shrinkage of the undercoat may occur after the application of the finishing coat due to the presence of clayey sand in cement or sand mixes.
It may be due to poor practices such as not applying enough pressure while working on the finishing coat of plaster.
8. Loss of Adhesion
The loss of adhesion of plaster may happen due to one of the below-listed reasons:-
Water penetration.
The finishing coat is stronger than the undercoat or wall.
The excessive thickness of all coats.
The dry backing out of the wet application or due to the lack of suction control during its application.
Lack of adequate key (first coat of plaster). The adequate key should be ensured by raking out the joints to 16 mm minimum depth. It can also be done by hacking the background or by scoring the underlying coat of plaster.
9. Conclusion
Proper care has to be taken after the completion of plastering. The curing process should start as soon as the plaster hardens. It must be cured for at least 7 days to reach the desired strength. Plastering is important as it helps in guarding the walls and other parts of a building against wear and tear. The buildings where the external walls are not plastered should be advised to be plastered. Only then the plaster can protect the walls against the rains and other harsh weather conditions.
An integral finishing step before painting, the plastering process should not be overlooked.
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