Plastering is the application of a mortar coat to the surfaces of walls, pillars, ceilings, etc. to obtain a smooth finish. The mortar used for plastering may be lime mortar, cement mortar or lime-cement mortar. The lime mortar used should have a coarse lime sand ratio of 1:3 or 1:4. If hydraulic lime is used the mixing ratio (lime:sand) is 1:2. Cement mortar of 1:4 or 1:6 mix is very common. Used for plastering, rich mixture is being used for exterior walls. To combine the cost-effectiveness of lime mortar and the good quality of cement mortar, many people use lime-cement mortar of 1:1:6 or 1:1:8 or 1:2:8 ratio (cement:lime:sand). use.
The purposes of plastering are:
- to conceal faulty workmanship
- Giving smooth surface to avoid dust catching.
- To give a good look.
- To protect the wall from rain water and other atmospheric agencies.
- To protect surfaces against vermitte.
Good plaster requires:
- It should easily follow the background.
- It should be hard and durable.
- It should prevent penetration by moisture
- It should be cheap.
Lime mortar is usually applied in 3 coats whereas cement mortar is applied in two or three coats for stone and brick masonry. Cement mortar for concrete surfaces can be applied in two or three layers.
Sometimes only one coat of cement mortar is applied to concrete building blocks.
The first coat provides a means of achieving a flat surface. Final coat provides smooth surface. If three coats are used then the second coat is known as the floating coat. The average thickness of the first coat is 10 to 15 mm. The thickness of the middle coat is 6-8 mm. The final coat is just 2 to 3 mm thick. If single coat is used then its thickness is kept between 6 to 12 mm. This type of coat is used on concrete surfaces that are not exposed to rain.
Instead of plastering the entire surface of the masonry, special mortar finishing work is performed on the exposed joints. This is called pointing. It involves raking the joints to a depth of 10 mm to 20 mm and filling it with a rich mortar mix. Pointing mix is used 1:2 in case of lime mortar and 1:3 in case of cement mortar pointing mix. Pointing stone is ideally suited for masonry as the stones have attractive colors and good resistance to penetration by water. Pointing gives completeness to the weak part of the masonry (In other words for joints) and it adds to the aesthetic view of the masonry.
The table below gives a comparison between plastering and pointing.
|no serial number||Plaster||pointing to|
|1.||It is applied over the entire surface.||It is provided only at exposed joints.|
|2.||It provides smooth surface.||It does not provide smooth surface.|
|3.||It hides faulty workmanship in masonry construction||It is used to highlight the beauty of well constructed masonry work.|
|4.||It provides the base for the white/colour wash||White washing or color washing is forbidden.|
Also read: 7 Forms Of Defects In Plaster
Read also: How to plaster the surface of the wall