PLASTERING

To get smooth finish are termed as plastering applying mortar coats on the surfaces of columns, walls ceiling etc.. Mortar used for plastering can be cement mortar, lime mortar, or lime-cement mortar. Lime mortar used will have fat lime to sand ratio of 1 : 3 or 1 : 4. If hydraulic lime is utilized mix proportion (lime: sand) is 1 : 2. Cement mortar of 1 : 4 or 1 : 6 mix is normally used for plastering, for outer walls richer mix being used. To merge the cost effectiveness of lime mortar and good quality of cement mortar many use lime-cement mortar of proportion (cement : lime : sand) of 1 : 1 : 6 or 1 : 1 : 8 or 1 : 2 : 8.

The objective of plastering is following:

1.  To give smooth surface to ignore catching of dust.
2.  For conceal defective workmanship
3.  From rain water and other atmospheric agencies it protects the wall.
4.  To provide good look.
5.  To protect the surfaces against vermit.

Requirement of good plaster are:

1.  It should be durable and hard.
2.  It must prevent penetration by moisture
3.  It should easily adhere to the background.
4.  It should be cheap.

Usually Lime mortar is applied in 3 coats whereas cement mortar is applied in two or three coats for brick masonry and the stone. Cement mortar may be applied for concrete surfaces in two or three coats. Many times only one coat of cement mortar is applied for concrete building blocks.

First coat provides means of getting level surface. Final coat provides smooth surface. If three coats are used second coat is called as floating coat. Average thickness of first coat is 10 to15 mm. Middle coat thickness is 6-8 mm. Final coat is 2 to 3 mm thick only. If single coat is used its thickness is kept between 6 to 12 mm. Such type coats are used on concrete surfaces not exposed to rain.