The brief descriptions of different types of paints are given below:
(1) Aluminium paint: The 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. The advantages of an aluminium paint are as follows:
(i) It is visible in darkness
(ii) It resists heat to a certain degree.
(iii) The surfaces of iron and steel are better protected from corrosion by this paint than any other paint.
(iv) It possesses a high covering capacity. A litre of paint can cover an area of about 200 m2.
(v) It gives good appearance to the surface.
(vi) It is impervious to the moisture.
(vii) It possesses high electrical resistance.
The aluminium paint is widely used for painting gas tanks, hot water pipes, marine piers, oil storage tanks, radiators, etc.
(2) Anticorrosive paint: This paint essentially consists of oil and a strong drier. A pigment such as chromium oxide or lead or red lead or zinc chrome is taken and after mixing it with some quantity of very fine sand, it is added to the paint. The advantages of an anticorrosive paint are as follows:
(i) It is cheap.
(ii) It lasts for a long duration.
(iii) The appearance of the paint is black.
(3) Asbestos paint: This is a peculiar type of paint and it is applied on the surfaces which are exposed to the acidic gases and steam.
(4) 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 pains is available. The paint presents a black appearance and it is used for painting ironwork under water.
(5) Cellulose paint: This paint is prepared from nitro-cotton, celluloid sheets, photographic films, etc. An ordinary paint hardens by oxidation. A cellulose paint hardens by evaporation of thinning agent. It thus hardens quickly. It is a little more costly, but it presents a flexible, hard and smooth surface. Also, the surface painted with cellulose paint can be washed and easily cleaned. The cellulose paint is not affected by contact with hot water and the surface can stand extreme degrees of cold and heat.
(6) Cement paint: This paint consists of white cement, pigment, accelerator and other additives. It is available in dry powder form. The 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. For external finish, on cement-plastered walls, it is mixed with water immediately before its application. It is desirable to provide cement paint on rough surface rather than on smooth surface because its adhesion power is poor on smoothly finished surface.
For painting surfaces like corrugated iron sheets, etc., the cement paint is mixed with boiled linseed oil. The mixture is constantly stirred during use.
The cement paint is applied in two coats. Before the first coat is applied, the surfaces are wetted to even and control suction and to assist the hardening process of the cement paint. It should however be seen that there is no presence of liquid water on the surface when the paint is applied. The application of paint over a surface exposed directly to hot sunlight should be avoided. Otherwise the coating will dry before it is cured and will become chalky.
The second coat is applied not less than 24 hours after the first coat and it considerably helps in improving the appearance of the surface. For tropical countries, the rewetting of surface before the application of second coat is absolutely necessary. It is also essential to keep the surface wet after the final coat for about 2days by frequent splashing of water to get the best performance. The application of cement paints during freezing weather should be avoided.
Following are the advantages of cement paints:
(i) It requires less skill and time for applying cement water paints and the applying implements can be cleaned with water only.
(ii) The preparation of surfaces is easier in a cement paint system as it is not necessary to remove the previous coats of cement paints.
(iii) They are suitable for painting fresh plasters having high alkalinity because cement paints are not likely to be attacked by the alkalinity of masonry surfaces.
(iv) They become an integral part of the substrata and add to its strength.
(v) They can be applied over new and damp walls which cannot be painted over with oil paints until they are sufficiently dried.
(vi) They prove to be economical as compared to the oil paints and they dry more rapidly than the oil paints.
Following precautions should be taken to avoid defects or complaints of the cement paints:
(i) The defect of cracking occurs when the film of paint has not adequate flexibility to move with thermal or moisture movements in the surface.
The cement paints however become integral part of the surface, if they are suitably cured and hence they do not move independently of the surface.
(ii) The efflorescence or crystalline deposits are sometimes seen on the finished surfaces. Such defects are mainly due to the nature of surface before application of paint or due to some external factor like highly saline atmosphere.
(iii) The flaking or lifting of the paint film due to loss of adhesion can be prevented by properly curing the surface after the application of paint.
(iv) The most common fungi or micro-organisms found in paints and coatings are moulds and they are attached to paint coatings by mycelial hairs which extend into and under the coatings. Such defects can be removed by scrubbing the surface with brush or by applying suitable fungicides or by adding the fungicides to the paint itself. A fungicidal wash may also be used effectively to retard fresh growth.
(v) The paint should be cured sufficiently after application. It will avoid the phenomena of chalking of surfaces which indicates the paint film losing adhesion with the surface and becoming powdery.
(vi) The term fleeting is used to indicate the bleaching or fading of colours caused mainly by the exposure to the weather actions. This defect can be considerably made less conspicuous by choosing lighter shades of paints for such surfaces.
(7) Colloidal paint: No inert material is mixed in this type of paint. It requires more time to settle and is the process of settlement, it penetrates through the surface l may be used for interior as well as exterior walls.
(8) Emulsion paint: A variety of emulsion paints is available. It contains binding materials such as polyvinyl acetate, synthetic resins, etc. This paint is easy to apply and dries quickly in about l Â½ to 2 hours. The colour of the paint is retained for a long period and the surface of paint is tough and it can be cleaned by washing with water. There is absence of odour and the paint possesses excellent alkali resistance.
The application of emulsion paint cam be carried out either by brush or spray gun. For long service life. It is recommended to apply tare coats of emulsion paint. For rough cement plastered surface, a thin cost of cement paint may first be applied to smoothen the surface. It is necessary to have a sound surface to receive the emission paint.
(9) 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 hand and durable surface. The surface provided with this paint is not affected by acids, alkalies, alkalies, fumes gas, hot and cold water and 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.
(10) Graphite paint: The paint presents a black colour and it is applied on iron surfaces which come in contact with ammonia, chlorine, Sulphur gases, etc. It is also used in mines and underground railways.
(11) Inodorous paint: No turpentine is used in chis paint, but whine lead or zinc white is mixed with methylated spirit. The white lead or zinc white is well ground in oil. The 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.
(12) 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 surfaces witch are free form corrosion or any other lead paint.
(13) 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 opacity and low gloss.
It should be remembered that the oil paint should not be applied during humid and damp weather. The presence of dampness on wall surface also considerably affects the life of oil paint coating. It is advisable to redecorate the surfaces finished with oil paint with a coating of fresh oil paint only. The layer of old oil paint serves as a foundation for the fresh paint.
(14) 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 cither by brush painting or spray painting. This paint possesses pleasing appearance and it is attractive in colour. This paint is widely used for show rooms, auditoriums, etc.
The plastic emulsion paints were introduced in our country in 1055 or so and they are becoming more and more popular day by day. An emulsion is a liquid having fine suspended particles of a substance. For plastic emulsion paints, the emulsion is composed of plastic compounds such as vinyl acetate and acrylate which are held in water. The typical composition of one litre of plastic emulsion paint is as follows:
2 N Binders
5 N Pigments
1 N other solids
6 N Water/14 N Total weight
When the paint dries, the water evaporates and a film of binders, pigments and other solids is left behind. One litre of plastic emulsion paint covers about 15 m2 of wall surface per coat, For interior jobs, the two coats of paint are sufficient, each coat having a thickness of about 0.04 mm.
(15) Silicate paint: This paint is prepared by mining 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. It is not affected by alkalies. No chemical action takes place on metals by this paint. The drier used with this paint should be of a special silicate drier type.
The silicate paint can directly be applied on brick, plaster or concrete surfaces. These surfaces should be made wet before the paint is applied.
The two or three coats of silicate paint are recommended and it is not necessary to have a priming coat. The tool which is used to apply silicate paint should be immediately cleaned with water after use. The surfaces should not be silicate paint in hot weather.
(16) Synthetic rubber paint: This paint is prepared from resins. It has the following advantages:
(i) It offers good resistance to the water and is not affected by heavy rains.
(ii) It dries quickly.
(iii) A uniform colour is maintained when this paint is applied on the surface.
(iv) It is little affected by weather and sunlight.
(v) It can be applied on surfaces which may not be completely dry e.g. fresh concrete.
(vi) It is moderate in cost and covers a sizeable area.
(vii) It is easy to apply on the surface.
(viii) It possesses excellent chemical resisting property.
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