Paints are applied on the surfaces of timber, metals, and plastered surfaces as a protective layer. and at the same time to get a pleasant appearance.
Paints are applied in liquid form and after some time the volatile constituent evaporates and hardened coating acts as a protective layer.
Constituents of Paint:-
The essential constituents of paints are:
- A vehicle
- A pigment
- A drier
- A thinner.
- It is a principal constituent of paint. It also possesses the binding properties.
- It forms an opaque coating.
- Commonly used bases for paints are white lead, red lead, zinc oxide, iron oxide, titanium white, aluminum powder, and lithophone.
- Lead paint is suitable for painting iron and steelworks, as it sticks to them well. However, it is affected by atmosphere action and hence should not be used as the final coat.
- While zinc forms a good base but is costly.
- Lithophone, which is a mixture of zinc sulfate and barytes, is cheap. It gives a good appearance but is affected by daylight. Hence it is used for interior works only.
- The vehicles are the liquid substances that hold the ingredients of paint in liquid suspension and allow them to be applied on the surface to be painted.
- Linseed oil, Tung oil, and Nut oil are used as vehicles in paints.
- Of the above four oils, linseed oil is a very commonly used vehicle. Boiling makes the oil thicker and darker. Linseed oil reacts with oxygen and hardens by forming a thin film.
- Pigments give the required color for paints. They are fine particles and have a reinforcing effect on the thin film of the paint.
- Pigments can be classified as either natural or synthetic.
- Natural pigments include various clays, calcium carbonate, mica, silicas, and talcs. Synthetics would include engineered molecules, calcined clays, blanc fixe, precipitated calcium carbonate, and synthetic pyrogenic silicas.
4. The Drier:
- These are the compounds of metal like lead, manganese, cobalt.
- The function of a drier is to absorb oxygen from the air and supply it to the vehicle for hardening.
- The drier should not be added until the paint is about to be used.
- The excess drier is harmful because it destroys elasticity and causes flaking.
5. The Thinner:
- It is known as solvent also.
- It makes paint thinner and hence increases the coverage.
- It helps in spreading paint uniformly over the surface Turpentine and naphtha are commonly used thinners. After paint applied, thinner evaporates and paint dries.
Properties of an Ideal Paint:-
- It should be possible to apply easily and freely.
- It should dry in a reasonable time.
- It should form a hard and durable surface.
- It should not be harmful to the health of workers.
- It should not be easily affected by the atmosphere.
- It should possess an attractive and pleasing appearance.
- It should form a thin film of uniform nature i.e., it should not crack.
- It should possess good spreading power.
- It should be cheap.
Types of Paints:
- Oil Paint: These paints are applied in three coats-primer, undercoat, and finishing coat. The presence of dampness while applying the primer adversely affects the life of oil paint. This paint is cheap and easy to apply.
- Enamel Paint: It contains white lead, oil, petroleum spirit, and resinous material. The surface provided by it resists acids, alkalies, and water very well. It is desirable to apply a coat of titanium white before the coat of enamel is applied. It can be used both for external and internal walls.
- Emulsion Paint: It contains binding materials such as polyvinyl acetate, synthetic resins, etc. It dries in 1.5 to 2 hours and it is easy to apply. It is more durable and can be cleaned with water. For plastered surfaces, first, a coat of cement paint should be applied and then the emulsion point. Emulsion paint needs sound surfaces.
- Cement Paint: It is available in powder form. It consists of white cement, pigment, and other additives. It is durable and exhibits excellent decorative appearance. It should be applied on rough surfaces rather than on smooth surfaces. It is applied in two coats. The first coat is applied on the wet surface but free from excess water and allowed to dry for 24 hours. The second coat is then applied which gives a good appearance.
- Bituminous Paints: This type of paint is manufactured by dissolving asphalt or vegetable bitumen in oil or petroleum. It is black in color. It is used for painting ironworks underwater.
- Synthetic Rubber Paint: This paint is prepared from resins. It dries quickly and is little affected by weather and sunlight. It resists chemical attack well. This paint may be applied even on fresh concrete. Its cost is moderate and it can be applied easily.
- Aluminum Paint: It contains finely ground aluminum in spirit or oil varnish. It is visible in darkness also. The surfaces of iron and steel are protected well with this paint. It is widely used for painting gas tanks, water pipes, and oil tanks.
- Anti-corrosive Paint: It consists essentially of oil, a strong dier, leads or zinc chrome, and finely ground sand. It is cheap and resists corrosion well. It is black in color.
Application of Paint
The preparation of the surface for the application of paint is the most important part of the painting. The surface to be painted should not be oily and it should be from flakes of the old paint. Cracks in the surface should be filled with putty and then with sandpaper. Then primer is applied. Painting work should be carried out in dry weather. The undercoats and first coats must be allowed to dry before the final coat is applied.
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