Plastering is the process of covering the rough surfaces of walls, columns, ceilings, and other building components with a thin coat of plaster to make the surface smooth and durable.
Plastering on the externally exposed surface is called rendering.
Generally, cement plaster and lime plaster are used for plastering work.
2. Objectives of Plastering
a. To provide a smooth and finished surface.
b. To protect the surfaces against atmospheric effects.
c. To resist chemical actions.
d. To cover defects in the structure.
e. To give a decorative appearance.
3. Requirements for Good Plaster Material
The plaster material should fulfill the following requirements:
a. It should be hard and durable.
b. It should remain on the surface and should protect from chemical attacks and weathering actions.
c. It should have good workability.
d. It should have high strength and durability.
e. It should be cheap and should be easily available.
f. It should protect from penetration of nature.
4. Tools Used in Plastering
b. Metal float( wooden float / claying float)
c. Plumb Bob
d. Spirit level
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5. Types of Plaster Used In Plastering Work
There are two types of plaster used in plastering work. They are:
a. Lime Plaster
When lime is mixed with the sand in the presence of the proper quantity of water, it is called lime mortar/ lime plaster, and the process of covering the surface of the walls, slabs, and columns by using lime plaster is called lime plastering.
Plastering may be single-coated or multi-coated.
The proportion of lime and sand for lime plastering is generally taken as 1:3 to 1:4.
When cement and sand are mixed with the proper quantity of water; cement plaster is formed and the process of covering the surfaces with cement plaster is called cement plastering.
The generally used mixed proportion of cement and sand for cement plaster are 1: 4, 1:5, and 1:6.
Internal plaster – 1:6 or 1:5
External plaster – 1:4
Ceiling plaster – 1:3
The grade for cement plaster
|Grade Name||Mortar Mix (by Loose Volume)||Compressive Strength at 28 days (in N/mm2)|
|MM 0.7||1||8||0.7 to 1.5|
|MM 1.5||1||7||1.5 to 2.0|
|MM 3||1||6||3.0 to 5.0|
|MM 5||1||5||5.0 to 7.5|
|MM 7.5||1||4||7.5 to above|
6. Plastering Procedure
~ The application surface should be made rough by raking out.
~ In case of the presence of cavities or holes; fill it in advance with suitable material.
~ All joints and application surfaces are cleaned out with the help of water and a wire brush. No traces of oils or greases should be left.
~ The application surface should be wet for at least 6 hours before the application of plaster.
~ For obtaining the uniform surface level; patches of plaster of size 15 mm * 15 mm and having a thickness of about 10 mm are used( Patches are also known as fix dots ). Patches are fixed at an interval of 2m.
~ Verticality of fix dots is checked with a plumb bob and screeds are formed between dots.
~ Then, a base coat is applied to the surface between screeds using the trowel. The thickness of the base coat may vary between 9 to 15 mm.
~ The surface is levelled using a wooden float.
~ Let the base coat set but not let it dry. Then roughen the base coat by scratching.
~ Then surface or finishing coat is applied over the base coat.
~ The thickness of the finishing coat may vary between 2 mm to 3mm.
~ Finishing coat is levelled uniformly utilizing a wooden float.
~ Let the plastered surface try and after 12 hours; start the curing.
~ Curing should be done for at least 7 days to prevent problems like cracking in future.
( Note: Plaster should be always done from top to bottom. )
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