Paints are coatings of fluid materials which are applied as a final finish to all surfaces such as walls, ceil- ings, wood work, metal work, etc. The process of applica- tion of paint as a coating material is called painting. The ingredients of paints and their functions are discussed below.
Ingredients of Paint
1. Base
2. Carrier
3. Drier
4. Solvent
5. Colouring pigments
1. BASE: It is the main ingredient of paint. It hides the surface to be painted and imparts durability to the painted surface. Commonly used bases are white and red lead, zinc and iron oxides.
2. CARRIER: The carrier is a liquid which acts as a binder and helps to spread the ingredients uniform- ly on the painted surface. Linseed, Tung, Poppy, Sunflower oil etc are some of the commonly used car- riers.
3. DRIER: Driers are metallic compounds used in small quantities for accelerating the process of dry ing of paint film. Litharage, Lead acetate, Manganese dioxide and Cohalt are the driers com- monly used.
4. SOLVENT Solvent or thinner in a liquid which thins the paint film so that it can be easily applied on the surface and it helps the paint in penetrating through porous surfaces. Turpentine, petroleum, spirit and highly solvent naptha are commonly used as solvent.
5. COLOURING PIGMENTS: To obtain desired colour and shades of the paint, colouring pigments are added.
Characteristics and Used of Paints
CHARACTERISTICS OF A PAINT
i. It should dry quickly
ii. It should be easy to apply and cover large surface area
iii. It should not be harmful to health
iv. It should not react with the wall or wooden material
v. The paint should not be affected by weathering actions of the atmosphere
vii. The paint should be fairly cheap and economical
USES
i. Protects the surfaces from the weathering effects of the atmosphere and actions by other liquid, fumes and gases.
ii. Prevent the decay of wooden members.
iii. Prevent the corrosion of metallic surface.
iv. Provide a smooth surface for easy cleaning.
v. Provide pleasing, colourful and decorative appear- ance to the surfaces.
vi. Increase the life of the buildings.
vii. It covers the defective workmanship and materials.
TYPES OF PAINTS
1 OIL PAINT: This is an ordinary paint. It is generally applied in three coats namely priming coat, under- coats and finishing coats. It is very cheap and pos- sesses opacity and low gloss.
2. ENAMEL PAINT: Enamel paint consists of white lead or zinc white ground in a small quantity of oil and mixed with petroleum spirit and resinous mat- ter. It is available in different colours.
3. EMULSION PAINT: It is easy to apply and dries quickly. Colour of paint is retained for a long period. It can be cleaned by washing with water.
4. ALUMINIUM PAINT: Aluminium paint consists of aluminium powder suspended in spirit vamish or oil varnish. After the application of the paint the spirit becomes evaporated and the aluminium is deposited on the surface as thin layer. Aluminium paint has the advantage such as visibility in darkness, imper- viousness to moisture, good appearance to the sur- face, high electrical resistance and resistance to heat and sunlight.
5. BITUMINOUS PAINT: It is prepared by dissolving asphalt or vegetable pigment in any type of oil or petroleum. It presents a black appearance. This type of paint is used to iron grills.
6. CEMENT PAINT: This type of paint is prepared by using white cement, pigment accelerators and other additives. It is available in a various colour and available in dry form. It is water dilutable paint. It is mainly applied on brick and cement surface and resists the penetration of moisture. It gives long life.
7. PLASTIC PAINT: The paint contains necessary variety of plastics. It is available in the market under different trades and colours. The plastic paint can be applied either by brush or by spray painting. It gives recreation, pleasing and good appearance.
Method of Painting old and new wood work
PREPARATION OF SURFACE FOR PAINTING OF THE OLD WOOD WORK
i. The surface of the old wood work should be cleaned by using sand paper.
ii. Old surface should be cleaned by using a litre of water mixed with 200 gm of caustic soda and lime to remove the old colours.
iii. Nails if any should be removed.
PROCEDURE OF PAINTING OLD WOODEN SUR- FACE
i. Priming coat is applied on the surface to reduce quantity of oil paint.
ii. After drying of the priming coat the first coat of paint is applied on the surface.
iii. After drying of the first coat of paint second and third coats will be applied on the surface subsequently.
METHOD OF PAINTING NEW WOOD WORK
1. PREPARATION OF SURFACE FOR PAINTING: The surface to be painted should be carefully cleaned and rendered smooth.
2. KNOTTING: Knotting is of three types. The com- monly adopted two types are discussed below.
i. ORDINARY KNOTTING: This is applied in two coats. The first coat consists of hot lead ground in water with a strong glue added to it. By doing this knots are removed.
ii. PATENT KNOTTING: This consists of two coats of varnish which is made by dissolving shellac in methylated spirit. Knots are removed by applying this mixture. Boiled lime is also used to remove knots.
3. PRIMING COAT OR FIRST COAT: After knotting the priming or first coat is applied to the whole sur- face of the wooden article to be painted.
4. STOPPING: After priming the process of stopping is carried out. After stopping dries, the surface is well rubbed down with emery sheets and cracks if any are filled with putty. This is known as stopping.
5. APPLICATION OF THE SUCCEEDING COAT: Painting is done by good quality brush. Finally, two coats of paint are applied one after the other. The second coat is applied only after the first coat is thor- oughly dried. While painting, the brush is held at right angles to the surface and only the hairs should touch the surface. If necessary after drying of second coat the third coat is also applied.
Method of Painting old and new Iron and Steel Works
PAINTING THE OLD IRON AND STEEL WORK
1. PREPARATION OF THE SURFACE
i. The iron and steel work to be painted is made free from all mill scale, loose rust and grease by using iron brushes.
ii. The old paint on the iron work should be cleaned by using phosphoric acid.
2. PAINTING THE OLD IRON AND STEEL WORK
1. The surface to be painted is cleaned with emery sheet.
2. Holes if any on the surface should be filled with metallic paste. Then as the priming coat, red oxide is applied on the surface. This is cheap. Painting adheres well on it.
PAINTING THE NEW IRON AND STEELWORK
1. PREPARATION OF THE SURFACE: The iron or steel work to be painted is made free of all mill scale, loose rust and grease by using iron brushes. The loos- ened scales are removed by a jet of hot water, fol- lowed by a bath of hydrated lime and petroleum.
Cleaned metal surface is finally treated with phos. phoric acid.
2. APPLICATION OF COATS OF PAINT: Surface of steel work is cleaned and dried. After this a priming coat is applied. After this has dried the second coat of paint is applied by using brush or spray. The com- pleted paint surface should be smooth and uniform.
Procedure of Cement Painting on Wall Surface
PREPARATION OF SURFACE
i. Newly constructed wall surface is wet. The wall sur- face should not he painted until it is completely dry. Time duration for drying depends on the ventilation and weather condition. Painting on a freshly plas- tered surface should be avoided for atleast 3 to 6 months
ii. The wall surface should be prepared well before painting to remove free lime or cement in the wall. Otherwise it will discolour the paint and destroy its oil. To avoid this priming coat is applied which does not consist of chemicals that reacts with alkaline
iii. Painting should be done only after the surface is given a coat of sizing (glue mixed with water) to fill up the cracks
iv. White patches that occurs on the plastered surface can be removed by water washing with wire brush. If white patches appear occurs again painting should be delayed
v. While painting, if any change occurs antisesptic washing treatment is given.
APPLICATION OF CEMENT PAINT
i. Initial coat of white cement is applied on the exteri- or walls
ii. After curing is completed first coat primer is applied,
iii. Above the primer coat 2 coats of cement paint is applied. Hence incomplete portions are finished by the second coat
iv. Finishing coat is applied in the opposite direction of the previous coat.
Important Points to be Considered while Painting
BRUSH: Brush used for painting should be of fibre bristles and not by using horse hairs. Only then more quantity of paint could be taken by the brush which will facilitate for easier painting. The brush should be cleaned by kerosene after the application of the paint.
ii. PAINTS: Ready mixed paints available in the mar- ket can be used. Since it is highly expensive two or more colours of paint are kept in stock and the required colour may be changed according to the sit- uation. For this, paint is taken in a solid state in a container and it is stirred well by adding linseed oil. Then by adding pigments for a required colour and suitable ingredients the paint is prepared.
iii. KNOTTING: Before painting the wooden surface the process of removing knot on the surface by hiding it and painting over it is called knotting. Paint should be applied only after knotting.
iv. PRIMING COAT: A coat of cheap rate paint is applied.
v. STOPPING: After completing the first coat it should be rubbed by emery sheet and pumice stone. Then stopping is carried out and second coat is applied
vi. COATING: Generally painting should be applied in 2 or 3 coats. Application of first coat is called priming coat. Second coat is called base coat. Third coat is called final coat.
vii. SPRAY PAINTING: Instead of painting with ordi- nary brush the surface can also be painted with spray pistol by passing the air with pressure. This is called as “Spray painting”. Spray painting is better then painting with brush. It includes special features like speed, quality, economy & labour.
