Plastering - Requirements, Types and Specifications

Anonymous February 18, 2019
Plastering is a work carried out to cover the rough surface of the building elements like a wall and ceilings by using a coat of plaster so that a smooth and durable surface is obtained.

The process of plastering helps to bring beauty, durability, and higher resistance to rain penetration for the element that is plastered. The term plastering is used to express the internal work. While the exterior work is termed by the name rendering.


The basic requirements of a good plaster, the main objectives of plastering, the types, and their specification are explained in the following section.

Plastering in Construction

The term plastering is commonly used for both internal and exterior work. The plastering is carried out based on the nature of the walls, whether it is external or interior walls. The exterior plastering works make the surface to be impermeable to rain. The inside plastering will facilitate smooth surfacing for painting works. These provide good aesthetic finishes.

When you look at the different layers of plaster that have to be applied on the wall surface, a single thick coat will result in sagging due to weight. Hence the thick plastering if necessary is carried out in two to three coats. 

For super finish coats and external cement plastering, two coats are used. The first coat is called the base coat or the rendering coat. The second or the last coat is called the finishing coat.

In lime plastering, three coats will be used. The first is called the rendering coat, the second coat is called the floating coat and the final coat is called the finishing coat. 

Requirements of a Good Plaster



The basic requirements of a good plaster are mentioned below:
  1. A good plaster mix must adhere to the surface during all the climatic conditions
  2. It must be cheap as well as economical
  3. The plaster must be hard and durable
  4. The plaster mix must be able to be applied at all the weather conditions
  5. The entry of the penetration of the moisture content from the surfaces must be examined and prevented by plaster
  6. The plaster must have adequate workability so that application is done as desired.


The plastering done for internal works are smoother on the surface. This will help in easy putty for painting works. Plastering is a solution for hiding the undesirable undulations seen in masonry, concrete casting works, or any other surface. But plastering must not be a complete solution for covering up extreme gaps and undulations. Improper concrete compaction will result in concrete structures that have large voids in the appearance that are seen after casting. This will make the cost of plastering to be high.


GOOD MIX!!!
GOOD WORK!!!😊

While plastering the exterior surfaces, they are made rough than making smooth. This is because the rough surface helps in preventing rainwater penetration of the walls compared to the smooth surface. 



The sand that is used for plastering must be finer than that is used for mortar mix that is used for masonry works. This is because the coarse sand particles won't stick to the ceilings.
Superior finishes will demand putty finishes after plastering and before painting.

Objectives of Plastering

The main objectives of plastering are:
  1. To provide an even smooth surface, clean, durable, and regular. This will hence improve the appearance of the surface
  2. To conceal the defective workmanship
  3. To protect and preserve the surface
  4. To provide a base surface to facilitate the decorative finish
  5. To cover up the porous materials of the masonry and the trace of inferior quality works

Types of Plastering

There are three types of plastering based on the type of mortar used. They are:
  1. Lime Plastering
  2. Cement Plastering
  3. Mud Plastering

Lime Plastering

Lime plastering is the process of covering building surfaces or any other structural surface by using lime mortar in various proportions. These proportions will depend on the nature of the work and the number of coats that is to be applied.

Table -1 below shows the three coat application details using lime mortar.




Table .1: Lime Plastering Details

Cement Plastering

In order to facilitate plastering for external surfaces, cement plaster is an ideal choice. It is mainly chosen to work on surfaces that are more prone to damp conditions like reservoirs, water tanks, copings, floors, and bathrooms. These areas primarily require non-absorbent surfaces.  When the thickness required is greater than 15mm, the cement plaster is applied in two coats. The details are given in table-2.


Table.2: Cement Plastering

Mud Plastering

Mud plastering is the cheapest of all plastering methods. This is employed for village house construction, temporary structures, and sheds. These are cheap and are high in insulation properties against heat. This will help in providing a comfortable living.

Specifications for Plastering

The plaster specification is more expressed through the number of coats say, single coats, two coats, or three coats. A single coat is enough for medium-cost buildings. But for higher resistance against the penetration works it is good to have two coats.
The general specifications for plastering on the brickworks and the block works are mentioned below:

Specifications for Lime Plastering

The general specification of Lime plastering are:
  1. Single Coat lime plaster -  12mm or 15mm
  2. Two coats of work lime plaster - 18mm or 20mm
  3. Three coats of lime plaster - 25mm
The lime plaster is prepared by using lime putty that is kept in standing water for at least 72 hours before their use. This will help in completely slaking the lime. The lime plaster must not be made from slaked lime.


Specification for Cement Plastering

The general specification for cement plastering are:
  1. Single coat cement plastering - 12 or 15 or 20mm
  2. Cement plaster with a floating coat of neat cement -  12 or 15 or 20mm
  3. Cement plaster 2 coats work - 18mm
  4. Cement ceiling plaster - 6mm
  5. Cement plaster for slab bearing - 6mm
  6. External rendering with cement plaster  2 coats- 18mm
The plaster that is employed must be plastic so that it can properly adhere to the masonry or the concrete surface. More cement in this will result in shrinkage, which is not desired. A slow-strength developing cement like C-33 grade than using a fast developing cement say C-53 for plastering. C-53 tends to crack more than C-33. 

Mix Proportions for Plastering

  1. Lime Mortar:   1:3 to 1:4
  2. Cement Plaster: 1:4 to 1:6
  3. Cement plaster for brickwork: 1:5 to 1:6
  4. Cement plaster for brickwork external:  1:4 to 1:5
  5. Cement plaster for partition (1/2 brick walls): 1:4
  6. Combination plaster employing fat lime:  1:1:8 to 1:2:8
  7. Ceiling plaster first coat and subsequent coats: 1:3, 1:4 to 1:5 respectively
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