Plastering is a process of covering tough surfaces and uneven surfaces with plastic material called plaster or mortar to obtain even, smooth, regular, clean & durable surface
A mixture of lime or gypsum, sand and water sometimes with fibre added, that hardened to a smooth solid and used for coating walls and ceiling.
Materials used in plaster:-
- Ordinary Portland cement (OPC)
- Lime or clay powder
- Admixtures (Optional)
Tools used in plastering:-
- Plasterer’s trowel:- Tools to scoop the plaster and apply it on the wall.
- Scraper:- To roughen the plaster surface for preparation of finishing plaster (sometime worker use their trowels to roughen the plaster applied)
- The hawk:- To hold or acts as a small reservoir for the pl;aster, while plasterer apply plaster to the wall.
- Large bucket:- For mixing of plaster to take place.
- Angle bending:- for much easier and neater corner.
- Mixture:- For mixing purpose, better if it is a electrical motorized mixture for best mixing process.
Objective of plastering:-
- To provide even, smooth, regular, clean and durable finished surface with improved appearance.
- To preserve and protect the surface.
- To cover up the use of porous materials of the masonry work.
- To conceal defective workmanship.
Properties of good plaster:-
- It should be hard and durable.
- It should be possible to apply it during all weather conditions.
- It should adhere to the background and it should remain adhere during all climatic changes.
- It should be cheap and economical.
- It should offer good sound insulation.
- It should be high resistant to fire.
- It should effectively check the penetration of moisture from the surface.
Types of plastering:-
There are different types of plasters are available such as:
- Lime plaster
- Cement plaster
- Mud plaster
- Stucco plaster
1. Lime plaster :-
- When lime is used as a binding material it is called lime plaster.
- Lime plaster is a type of plaster composed of hydrated lime, sand and water.
- Lime plaster is similar to lime mortar, the main difference is based on use rather than composition.
- Mortar for lime plaster is usually prepared by mixing sand and lime in equal proportions, to improve the strength small quantity of cement is added to it.
2. Cement plaster:-
- When cement is used as a binding material it is called cement plaster.
- It is specially suited for damp condition.
- Cement plaster is usually applied in one coat.
- Thickness of coat can be 12 – 15mm or 20mm depending upon site conditions and type of building.
- 6mm thickness of plastering of 1:3 or 1:4 Ratio is recommended for cement plastering of RCC surfaces.
3. Mud plaster:-
- The surface to be prepared exactly in the same manner as that of for lime plaster or cement plaster.
- Mud plaster is generally applied in two coats, the first coat being 18mm thick while the thickness of second coat kept 6mm.
4. Stucco plaster:-
- Stucco is the name given to decorative type of plaster which gives an excellent finish.
- Stucco plaster can be used for interior as well as exterior surfaces.
- It is usually laid in three coats making the total thickness of plaster about 25mm. The first coat is called scratch coat, the second coatis called fine coat, it is also known as brown coat and the third coat is called white coat or finishing coat.
Types of finishing:-
- Smooth cast
- Pebble dash
- Rough cast
- Texture finish
- Scrapped finish
1. Smooth cast:-
- It is a finish which presents levelled and smooth surface.
- The mortar for finish is made by mixing of cement and fine sand in the ratio of 1:3.
2. Pebble dash:-
- It is a finish in which the small pebbles or crushed stones of suitable size are throne on to a freshly applied finish coat of plaster and left exposed.
- The mortar finish is made by cement and coarse aggregate of 1:3 ratio.
3. Rough cast:-
- It is a finish in which the mortar for the final coat contains a proportion of fairly big size coarse aggregates.
- The mortar for finishing is made by mixing cement, fine sand and coarse aggregate in the ratio of 1: 1/2:3
4. Textured finish:-
- In this finish ornamental patterns or textured surface are produced by working with various tools in the freshly applied final coat.
Defects in plastering:-
- Falling out of plaster
- Blowing of plaster
Cracking:- Appears on the plastered surface in the form of hair cracks or wider cracks, it is due to old surface is not properly dressed, bad workmanship or due to expansion and shrinkage in the plaster during drying.
Efflorescence:- It is soluble salts are present in the plaster making materials or bricks. They appear on the plastered surface in whitish patches and produced ugly appearance.
Blistering:- Small patches well out beyond the plastered surface like boils.
Falling out of plaster:- Due to excessive thermal variation in plaster, inadequate bonds between the coats of plaster and due to imperfect adhesion of the plaster to the background
Prevention of defects:-
Cracking:- it can be avoided by continuous damping of the plaster in order to slow down any rapid drying, to prevent the cracking from happening.
Efflorescence:- It may removed by brushing and washing of the surface for several times
Blistering:- usually caused due to uneven mixing of plaster, which would be prevented by ensuring a sufficient mixing between cement and it’s components to form plaster.
Falling out of plaster:- thermal variation can be minimized by means of water sprinkling method on the surface of the wall to reduce excessive thermal differences. For the case of inadequate binding, it can be prevented by ensuring plaster are plastic (workable) enough to stick into the wall. Imperfect adhesion can be minimized by art of good workmanship.
Ensure to apply enough pressure to the plaster while plastering, to ensure the plaster mortar goes into any deep irregular surfaces and cover the the holes if any present in wall as much as possible.
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