PAINTS

PAINTS

Paints are applied on the surfaces of timber, metals and plastered surfaces as a protective layer and at
the same time to get pleasant appearance. Paints are applied in liquid form and after sometime the
volatile constituent evaporates and hardened coating acts as a protective layer.

Constituents of Paint

The essential constituents of paints are:
1. Base
2. A vehicle
3. A pigment
4. A drier and
5. A thinner.

1. Bases: 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, aluminium powder and lithophone. A lead paint is suitable for painting
iron and steel works, as it sticks to them well. However it is affected by atmosphere action
and hence should not be used as final coat. While zinc forms good base but is costly.
Lithophone, which is a mixture of zinc sulphate and barytes, is cheap. It gives good appearance
but is affected by day light. Hence it is used for interior works only.

2. Vehicles: The vehicles are the liquid substances which hold the ingredients of a 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 very
commonly used vehicles. Boiling makes the oil thicker and darker. Linseed oil reacts with
oxygen and hardens by forming a thin film.

3. Pigment: Pigments give required colour for paints. They are fine particles and have a
reinforcing effect on thin film of the paint. The common pigments for different colours are:
Black—Lamp black, suit and charcoal black.
Red—venedion red, red lead and Indian red.
Brown—burned timber, raw and burned sienna
Green—chrome green, copper sulphate.
Blue—prussian blue and ultra marine
Yellow—ochre and chrome yellow.

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 Terpentine and neptha are
commonly used thinners. After paint applied, thinner evaporates and paint dries.

Properties of an Ideal Paint
1. It should be possible to apply easily and freely.
2. It should dry in reasonable time.
3. It should form hard and durable surface.
4. It should not be harmful to the health of workers.
5. It should not be easily affected by atmosphere.
6. It should possess attractive and pleasing appearance.
7. It should form a thin film of uniform nature i.e., it should not crack.
8. It should possess good spreading power.
9. It should be cheap.

Types of Paints
Depending upon their constituents there are various types of paints. A brief description of some of them which are commonly used are given below:
1. Oil Paint: These paints are applied in three coats-primer, undercoat and finishing coat. The
presence of dampness while applying the primer adversely affect the life of oil paint. This
paint is cheap and easy to apply.

2. 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.

3. 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.

4. 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. First coat is applied
on wet surface but free from excess water and allowed to dry for 24 hours. The second coat
is then applied which gives good appearance.

5. Bituminous Paints: This type of paint is manufactured by dissolving asphalt or vegetable
bitumen in oil or petroleum. It is black in colour. It is used for painting iron works under
water.

6. 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.

7. Aluminium Paint: It contains finely ground aluminium 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.

8. Anti-corrossive Paint: It consists essentially of oil, a strong dier, lead or zinc chrome and
finely ground sand. It is cheap and resists corrossion well. It is black in colour.

Application of Paint
Preparation of surface for application of paint is the most important part in 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 sand paper. Then primer is applied. Painting work should be carried out in dry weather. The under coats and first coats must be allowed to dry before final coat is applied.

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