PAINTSPresented By.

Engineer LATIF HYDER WADHO

Paints:Paints are used to protect metals, timber or plastered surfaces, brick work and concrete work from the corrosive effects of weather, heat, moisture or gases etc and to improve their appearance. Composition of the paints can be easily adjusted in the process of their manufacture, depending upon the purpose for which they are required and quality of the work required.

• CONSTITUENTS/ COMPOSITION OF PAINTS:Paints essentially contain a base which provides body, there is a carrier, also known as vehicle in which the base is dissolved, and it is the carrier which helps the base to spread all over when applied. The pigments are also added to give the desired colours. Some common examples of substances used as base in paint are zinc white, white lead, red lead. Common substances used as carrier in the paints is such as, water (in water paints), linseed oil and poppy oil etc.Continued -------

Besides these essential ingredients, several other substances are added, such as fillers to give bulk to the paint without affecting its properties and to make it economical, solvents or thinners which dissolve other constituents and make the paint thin and driers which help in rapid drying, setting and hardening of the painted surface. Some commonly used fillers for paints are chalk, silica and charcoal, commonly used solvents are turpentine oils, petroleum sprit, commonly used driers are red lead, litharge and manganese sulphates etc.

USES OF PAINTS:The main functions performed by paints are:• It is used to give a high-class finish,• It is used to give attractive colours,• It is used to give pleasing surfaces design

and appearance,• It is also used to protect the material from

atmospheric effects,• To protect various substances from corrosion,• To protect wooden articles from wet-rot and

many other types of defects,• To make the materials long lasting.

PROPERTIES OF GOOD PAINTS :The main properties of a good paint are as follows:• It should give a thin and uniform coating.• It should be hard and durable on drying.• The painted surface should not crack on drying.• It should be resistant to weathering and corrosive

action.• It should be water-repellent (except water paints).• It should have good spread.• It should have good adhesive power. It should

give a good finish with attractive colour, design and appearance.

• The colours should be fast and permanent.• It should be cheap and economical.

CLASSIFICATION OF PAINTS:

Paints in common use areclassified as:

(1) Oil Paints:The oil paints are very widely and commonly used for painting wooden and metallic surfaces in all kinds of engineering, industrial and other decorative works. In these paints various oils like linseed oil, poppy oil and castor oil etc are used as carrier. These paints are available in different colours and under different trade names. While using these paints it is proper to give two to three coatings so as to obtain good results.

(2) Plastic Paints:• In addition to other ingredients this

paint contains the requisite amount of plastic. That is why; all such paints are known as plastic paints.

• Plastic paints are used wherever high class work is required, such as sophisticated buildings, show-rooms, theatres and auditoriums. They can be easily applied on the plastered walls.

 

(3)Cement Paints:• The cement paint essentially consists of White

Cement (about 70%), Hydrated Lime (about 15%), Pigments (about 5 to 8%), Sodium or Calcium chloride as the hygroscopic salts (about 5%) and small amount of about 1% aluminium. These paints are made available in powder form. Water is added to the paint just before use. It is necessary to mix the paint from time to time while using it. The plastered surface to be painted, like walls etc are first made wet. As the painted surface dries, water is again sprinkled over it for proper setting of the paint.

• Cement paints mainly used over the plastered surfaces.

(4) Bituminous Paints:Bituminous paints are prepared by dissolving bitumen in petroleum or other solvent oil. These black coloured paints leave hard, tough and elastic surfaces. These are highly resistant to water and are specially used for submerged iron and steel structures.

(5) Water Paints:A water paint is the mixture of pigment, binder, drier and water (the carrier). Casein is the most common binder used in these paints. A variety of pigments are used to obtain different colours. These paints are cheap, easily workable and also washable when properly set. They also give a good finish and are suitable for the inside walls.

(6) Distemper Paints: Distemper consists of chalk (finely powdered), pigment and glue (animal glue). These are in powder form and available in a large variety of attractive shades. Sometimes these are available in the form of paste also (with the addition of linseed oil). These are mixed with water at the time of use and applied on the plastered surfaces (like walls, ceilings etc) with brushes. These may be considered as superior quality water paints. However they give a better finish and are long lasting. They are suitable for high-class interior decorative finishing work on the walls and ceilings of all kinds of buildings.

THE PLEASANT END