The art of treating the surface with a suitable covering material to make them weather resisting and decorative is called surface finishing.
Examples: Plasters, paints, varnishes, white wash, color wash, distemper etc.
a. To protect the surfaces from the effect of weathering agencies.
b. To provide decorative finish which adds pleasing appearance to the surface
c. To provide a smooth surface.
IMPORTANT TECHNICAL TERMS
Some important terms concerning to surface finishing are discussed below:-
1. Background: The surface to which the first coat of plaster is applied is called background.
2. Dubbing out: The process of filling the hollow spaces of the background for applying the plaster is termed as dubbing out.
3. Hacking: The process of making the back ground rough to act as key for plastering is called hacking.
4. Gauging: The mixing of various constituents of plaster is called gauging.
5. Rendering Coat: The first coat of plaster is called rendering coat or rough course.
6. Under Coats: The coats of plaster or paints applied under the finishing coat are known as under coats.
These coats are applied to provide a smooth, uniform and sound surface for the finishing or final coat.
7. Finishing Coat: The final layer of the surface finish is known as finishing coat.
8. Peeling: The removal of the plaster from the back ground is called peeling.
9. Blistering: The local swelling of a finished plastered or paint surface is known as blistering
This is due to lack of adhesion of the plaster or paint with the surface.
10. Cracking: The development of angular fractures, cracks in a plastered surface is called cracking.
In case of painting, it indicates the presence of a soft under coat.
11. Checking: The longitudinal split in a painted or plastered surface is known as checking.
It is caused due to uneven shrinkage on account of rapid drying.
12. Chalking: The dull and powdery appearance of a painted or plastered surface is known as chalking.
It indicates insufficient or inferior binding material used in the paint or plaster.
13. Erazing: The irregular development of hair cracks on a plastered surface is termed as erasing.
14. Dado: The special treatment provided to plastered walls at their lower level, usually in bath rooms and W.C’s is called dado.
It is provided up to 1.5 m height from the floor level. It may be consisting of rich cement mortar, glazed tiles etc.
15. Skirting: The special treatment provided to plastered walls at their lower level, usually in drawing and living rooms of a building is called skirting.
It is provided up to 15 cm height from the floor level. It is usually consisting of the material which is used for providing margin or border of flooring.
The art of covering the surface of the masonry work with a suitable plaster is called plastering.
The plaster used may be cement plaster, lime plaster or any other specified plaster.
The finished surface of walls, constructed in bricks or stones are generally so coarse textured that they provide unsuitable finish for the internal walls of most of the buildings. These surfaces are rendered smooth by the application of two coats of plater. The ceilings are also rendered smooth with plaster.
Purposes of plastering:
a. To provide an even, smooth, regular, clean and durable finished surface.
b. To protect the surface from the effects of weathering agencies.
c. To conseal the defective workmanship.
d. To cover inferior quality of materials used in the masonry.
e. To provide a smooth base for decorative surface finishes.
f. To protect the surface against dust, dirt and vermin nuisance in case of internal plastering.
Requirements of an ideal plaster:
a. It should adhere firmly to the surface.
b. It should not contract in volume while drying and setting.
c. It should be durable enough to resist the effects of weathering agencies.
d. It should offer good resistance against fire.
e. It should provide a smooth, non-absorbent and washable surface.
f. It should provide the surface with required decorative effect.
TYPES OF PLASTERING:
The various types of plastering are classified as follows:
a. Cement plastering
b. Lime plastering
c. Mud plastering
d. Stucco plastering
e. Moghul plastering.
Final treatment with cement or lime mortar made to the joints of the masonry to provide neat appearance is termed as pointing.
The joints on the face of stone or brick masonry are roughly filled in while the walls are being raised. They are afterwards neatly finished off to make them water tight. These joints, thus finished, give a better appearance to the surface and prevent rain water from entering the interior of the masonry.
Purposes of Pointing:
a. To prevent the moisture and rain water from entering the interior of masonry through joints and to make them durable.
b. To improve the appearance of the structure.
Suitability: Pointing is preferred to plastering under the following circumstances:
a. Where a smooth and even surface is not essentially required.
b. Where it is desired to exhibit to view the natural beauty of the materials (bricks or stones) used in the construction.
c. Where the material can withstand the weathering action.
d. Where the workmanship is neat and good.
TYPES OF POINTING:
The selection of a particular type of pointing depends upon the type of bricks or stones used and the appearance required. Thus pointing is mainly classified into the following types:
a. Beaded pointing
b. Flat or flush pointing;
c. Struck pointing;
d. Recessed pointing;
e. V- pointing;
f. Weather pointing;
g. Keyed or grooved pointing;
h. Tuck pointing.
Beaded pointing: This type of pointing is shown in fig and it is formed by a steel or iron rod with a concave edge. Beaded pointing is good in appearance. But it is difficult to maintain as it can be easily damaged.
Flat or Flush Pointing: It this type of pointing, the mortar is pressed tightly and joints are filled up and made flush with the face of the wall as shown in fig
This is the simplest type of pointing and is provided extensively, it is economical and durable because it requires less labour than all other pointings. It also does not afford a lodging place for dust.
Struck Pointing: In this type of pointing, the face of the mortar joint, instead of keeping it vertical, its upper side is kept about 12mm inside the face of the masonry and the bottom is kept flush with the face of the wall as shown in fig.
This pointing has a better effect of throwing rain water. This is also known as ruled pointing. This pointing is the best in ordinary circumstances.
Recessed Pointing: In this type of pointing, the face of the mortar joint is pressed inside by means of a suitable tool and is left vertical instead of being made inclined as shown in fig.
This type of pointing is provided when the work of good textured bricks is provided and also good quality of mortar is used.
V-pointing: This type of pointing is provided by forming a V-shaped groove inside the mortar of the joint with a special tool (steel or iron jointer) as shown in fig.
This type of pointing is generally recommended for brickwork in case of government or public buildings.
Weather pointing: This is similar to V–pointing but in this case instead of pressing a v- shaped groove inside, it is provided by forming a V-shaped projection outside the wall surface as shown in fig.
This type of pointing is generally recommended for superior brickwork.
Keyed or grooved pointing: In this type of pointing, the joints are first filled up flush, then a circular piece of steel or iron is pressed and rubbed in the middle of joints. Grooved pointing has a big groove in the face than keyed pointing as shown in fig.
Keyed pointing gives an attractive appearance to the structure and is generally used for superior brickwork.
Tuck Pointing: in this type of pointing, the mortar joints are filled flush with the face of the wall. Then 6mm wide and 3mm deep grooves is immediately and carefully formed in the centre of the joint and the groove is filled with or tucked in with white lime putty as shown in fig. the lime putty is given a maximum projection of 6mm.
Tuck pointing has a neat and attractive appearance, but the lime putty is not durable and is due course of time, it becomes defective.
METHODS OF POINTING:
Pointing is carried out as follows:
a. The mortar of the masonry joints to be covered by pointing is raked out at least to a depth of 20 mm.
b. The dust from the masonry joints is removed by brushes.
c. The surface is then washed with clean water and it is kept wet for few hours.
d. The mortar is then carefully placed in desired shape in these prepared joints. The mortar is placed by a small trowel and it is slightly pressed to bring it into close contact with the old interior mortar of the joint.
e. The finished surface is well-watered for a period of at least 3 days, if lime mortar is used and 10 days, if cement mortar is used.
CHARACTERISTICS OF AN IDEAL PAINT:
a. It should possess a good spreading power, i.e. maximum area of the surface should be covered by minimum quantity of the paint.
b. The paint should be fairly cheap and economical.
c. The paint should be such that it can be easily and freely applied on the surface.
d. The paint should be such that it dries in reasonable time and not too rapidly.
e. The paint should be such that its colour is maintained for a long time.
f. The paint should form a hard and durable surface.
g. The paint should not be affected by weathering actions of the atmosphere.
h. The paint should possess attractive and pleasing appearance.
i. The surface coated with paint should not show cracks when paint dries.
j. When applied on the surface, the paint should form a thin film of uniform nature.
INGREDIENTS OF AN OIL BASE PAINT:
An oil paint essentially consists of the following ingredients:
ü A base,
ü A vehicle or carrier,
ü A drier,
ü A colouring pigment, and
ü A solvent.
Base: A base is a solid substance in a fine state of division and it forms the bulk of a pint. It determines the character of the paint and imparts durability to the surface which is painted.
ü White lead
ü Red lead
ü Oxide of zinc or zinc white
ü Oxide of iron
ü Titanium white
ü Antimony white
ü Aluminium powder
Vehicles: The vehicles are liquid substances which hold the ingredients of a paint in liquid suspension. They are required mainly for two reasons:
a. To make it possible to spread the paint evenly on the surface, and
b. To provide a binder for the ingredients of a paint so that they may stick or adhere to the surface.
ü Linseed oil
ü Tung oil
ü Poppy oil
ü Nut oil
Driers: The driers accelerate the process of drying. A drier absorbs oxygen from the air and transfers it to limited oil, which in turn, gets hardened. Driers have a tendency to injure the colour of paint and to destroy the elasticity of paint. They are, therefore, not generally used for the final or finishing coat of the paint. Various patented dries are available in the market. They may be either in the form of soluble driers or paste driers. The former driers are compound of metals such as cobalt, lead, manganese, etc. dissolved in linseed oil or some other volatile liquid. The latter driers are compounds of the same metal. But they are mixed with inert fillers such as barites, whiting, etc. and then ground in linseed oil. The inert fillers serve as adulterants and the weight of inert filler in a pint should not exceed one –fourth the weight of base. They are used for the following purposes:
a. To bring down the cost of paint;
b. To improve the durability of paint;
c. To modify the weight of paint; and
d. To prevent shrinkage and cracking.
Litharge, red lead and sulphate of manganese can also be used as driers. Litharge is the most commonly used drier. Red lead is less effective than litharge and it is to be used when its addition does not interfere with the tint of the paint. Sulphate of manganese is used with zinc paints so as to eliminate the risk of discolouring of a lead drier. Great care is required in mixing sulphate of manganese; otherwise spots will be formed on the painted surface.
Colouring pigments: When it is desired to have a different colour than the base of paint, a colouring pigment is to be added. There are five divisions of colouring pigments:
a. Natural earth colours such as ochres, umbers, iron oxides, etc.
b. Calcined colours such as lamp black, Indian red, carbon black, red lead, etc.
c. Precipitates such as Prussian blue, chrome green, chrome yellow, etc.
d. Lakes prepared by discolouring barites or china clay with the help of suitable dyes.
e. Metal powders such as aluminium powder, bronze powder, copper powder, zinc powder, etc.
ü Black – ivory black, vegetable black
ü Blue – indigo, Prussian blue
ü Brown – Burnt umber, raw umber
ü Green – Chrome green, copper sulphate
ü Red – Vermilion red, red lead, carmine
ü Yellow – yellow ochre, raw sienna, zinc chrome.
Solvents: The function of a solvent is to make the paint thin so that it can be easily applied on the surface. It also helps the paint in penetrating through the porous surfaces. The most commonly used solvent is the spirit of turpentine. Other solvent containing some part of spirit of turpentine are available. But they are inferior to pure spirit of turpentine. The purity of spirit of turpentine can be tested by evaporation. Pure spirit of turpentine does not leave any residue on evaporation. Turpentine is greatly affected by weather and hence, for exterior works, it should be taken in minimum quantity to make the paint workable on the surface.
TYPES OF PAINTS:
Brief descriptions of different types of paints are given below:
Aluminium paint: Very finely ground aluminium is suspended in either quick drying spirit varnish or slow- drying oil varnish as per requirement. The spirit or oil evaporates and a thin metallic film of aluminium is formed on the surface.
Anticorrosive paint: This paint essentially consists of oil and a strong drier. A pigment such as chromium oxide, lead, red lead or zinc chrome is taken and after mixing it with some quantity of very fine sand, it is added to the paint.
Asbestos paint: This is peculiar type of paint and it is applied on the surfaces which are exposed to acidic gases and steam.
Bituminous paint: This paint is prepared by dissolving asphalt or mineral pitches or vegetable bitumen in any type of oil or petroleum. A variety of bituminous paints is available. The paint presents a black appearance and it is used for painting ironwork under water.
Cellulose paint: This paint is prepared from nitro – cotton, celluloid sheets, photographic films, etc. an ordinary paint hardens by oxidation. Cellulose paint hardens by evaporation of thinning agent. It thus harden quickly. It is a little more costly, but it presents a flexible, hard and smooth surface.
Cement paint: This paint consists of white cement, pigment, accelerator and other additives. It is available in dry powder form. Cement paint is available in variety of shades and it exhibits excellent decorative appearance. It is water – proof and durable. It proves to be useful for surfaces which are damp at the time of painting or are likely to become damp after painting.
Colloidal paint: No inert material is mixed in this type of paint. It requires more time to settle and in the process of settlement, it penetrates through the surface. It may be used for interior as well as exterior walls.
Emulsion paint: A variety of emulsion paint is available. It contains binding materials such as polyvinyl acetate, synthetic resins, etc. this paint is easy to apply and it dries quickly in about 1 ½ to 2 hours. The colour of the paint is retained for a long period. The surface of paint is tough and it can be cleaned by washing with water. There is absence of odour and the paint possessed excellent alkali resistance.
Enamel paint: This paint is available in different colours. It contains white lead or zinc white, oil petroleum spirit and resinous matter. It dries slowly and forms a hard and durable surface. The surface provided with this paint is not affected by acids, alkalies, fumes of gas, hot and cold water, steam, etc. it can be used for both internal and external walls. In order to improve the appearance, it is desirable to apply a coat of titanium white in pale linseed oil before the coat of enamel paint.
Graphite paint: The paint presents a black colour and it is applied on iron surface which come in contact with ammonia, chlorine, sulphur gases, etc. it is also used in mines and underground railways.
Inodorous paint: No turpentine is used in this paint. But while lead or zinc white is mixed with methylated spirit. While lead or zinc white is well ground in oil. Shellac with some quantity of linseed oil and castor oil is dissolved in methylated spirit. The paint is not durable, but it dries quickly. The methylated spirit evaporates and a film of shellac remains on the surface.
Luminous paint: This paint contains calcium sulphide with varnish. The surface on which luminous paint is applied shines like radium dials of watches after the source of light has been cut off. The paint should be applied on the surfaces which are free from corrosion or any other lead paint.
Oil paint: This is the ordinary paint and it is generally applied in three coats of varying composition. They are respectively termed as primes, undercoats and finishing coats. This paint is cheap and easy to apply and it possesses good capacity and low gloss.
Plastic paint: This paint contains the necessary variety of plastics and it is available in the market under different trade names. The application of plastic paint can be done either by brush painting or spray painting. This paint possesses pleasing appearance and it is attractive colour in colour. This paint is widely used for showrooms, auditorium, etc.
Silicate paint: This paint is prepared by mixing Calcined and finely ground silica with resinous substances. The paint when dried forms a hard surface and it is durable. It can stand extreme heat and it adheres firmly to brickwork also.
Synthetic rubber paint: This paint is prepared from resins.
DEFECTS IN PAINTING:
Following are the usual defects which are found in the painting work:
a. Blistering: This defect is caused by the water vapour which is trapped behind the painted surface. The formation of bubbles under the film of paint occurs in this defect.
b. Bloom: In this defect, the formation of dull patches occurs on the finished polished surface. It is due to defect in paint or bad ventilation.
c. Fading: The gradual loss of colour is known as fading and it is mainly due to the effect of sunlight on pigments of paint.
d. Flaking: A small portion of the painted surface is sometimes seen loose. It is known as flaking and is due to poor adhesion.
e. Flashing: Sometimes glossy patches are seen on the painted surface. This is known as flashing and it is mainly due to bad workmanship, cheap paint or weather actions.
f. Grinning: When the final coat of paint has not sufficient opacity, the background is clearly seen. This known as grinning.
g. Running: The paint runs back and leaves small areas of surface uncovered. This defect occurs when the surface to be painted is too smooth.
h. Sagging: When a vertical or inclined surface is painted too thickly, the defect of sagging occurs.
i. Saponification: The formation of soap patches on the painted surface is termed as Saponification and it is due to chemical action of alkalies.
j. Wrinkling: When a horizontal surface is too thickly painted, the defect of wrinkling becomes prominent.
The term varnish is used to indicate the solution of resins or resinous substances prepared either in alcohol, oil or turpentine.
Following are the main objects of varnishing a surface:
a. It brightens the appearance of the grain in wood.
b. It renders brilliancy to the painted surface.
c. It protects painted surface from atmospheric actions.
Ingredients of a Varnish:
Following are the three ingredients of a varnish:
a. Resins or resinous substances
INGREDIENTS OF DISTEMPER
Distemper is composed of base, carrier, colouring pigments and size.
The term wall paper is used to indicate a roll paper material with a printed pattern. The material is pasted to the wall or ceiling surfaces and its application thus develops decorative finishing of interior walls.