PAINTS// INTERIOR DESIGN

 

Paint is applied on timber, metal, brick or other materials in the form of a liquid which, on drying, forms a thin film on the painted surface. The essential function of the paint film on the painted surface. The essential function of the paint film is to provide provide protection or decoration or both. Paint is indispensable for the proper maintenance and preservation of wooden structure against warping, checking or decay.

Paint is composed of two main components; pigment and organic binder. Pigment is the solid ingredient of the paint and is used in the form of a fine powder. Organic binder is the liquid part of the paint and it is called vehicle. The vehicle varies with the type of paint. It is usually linseed oil for an oil paint, varnish is kalsomine in case of enamel paints and it is water in case of cold water paints.

CONSTITUENTS OF AN OIL PAINT

An oil paint is generally made up of six main constituents given below:

Base

Inert filler or extender

Colouring pigment

A vehicle

A solvent or thinner

A drier

 

Base: It is generally a metallic oxide and is used in the form of powder. Base is essentially a pigment which forms the chief ingredient of a paint. The most important purpose of adding base or pigment in a paint is to make an opaque coating to hide the surface to be painted. In addition, it makes the film of coating resistant to abrasion and prevents shrinkage cracks likely to be formed in the film, during drying. While lead, red lead, zinc oxide, iron oxide and titanium whites are the bases commonly used.

Inert filler or Extender: It is a cheap pigment added in a paint to reduce its cost. In addition, it modifies the weight of the paint and makes it more durable. With proper formulations, the inert filler pigments may be helpful in contributing useful properties to the paint film. The commonly used inert fillers or extenders are; Barytes, lithopone, silica, silicate of magnesia of alumina, whiting, gypsum, charcoal etc.

Colouring pigments: As the name indicates, it is a white or coloured pigment, mixed in a paint to get the desired colour of the paint.

Vehicle: It is a liquid which acts as a binder for the various pigments, base, extender and colouring pigment. The vehicle makes the paint in the state of a fluid and thus helps to spread its ingredients uniformly over the surface to the painted. This forms as elastic, resistant to abrasion and reasonably impermeable film on drying. Refined linseed oil is a commonly used vehicle in oil paints. Tung, perils, soyabean, fish, sunflower, tobacco seeds are also being used as vehicles in various combinations with linseed oil or without linseed oil.

Solvent or Thinner:It is a liquid which thins the consistency of the paint and evaporates after the paint film has been applied. It imparts to the paint film good properties such as brushability, smoothness and easy flow. Turpentine’s, pure oils, petroleum spirit and highly solvent naphtha are commonly used as thinner.

Drier: These are materials containing metallic compounds and are used in small quantities for accelerating the drying of paint film. They act as catalysts for the oxidation and polymerization of the vehicle used in the paint. Litharge, lead acetate, manganese dioxide and cobalt are the driers commonly used. If used in excess especially in the final coat, they tend to destroy the elasticity of the paint which finally leads to its flaking.

CHARACTERISTICS OF A GOOD PAINT:

A good paint should have the following characteristics:

1.It should stick well to the surface and should be able to seal     the porous substrata.

2. Its consistency should provide easy workability.

3. The thickness of the paint film should be adequate for good protection and decoration of the surface.

4. The paint film should dry rapidly.

5. The dried paint film should be able to withstand the adverse weather effect for a long time without losing gloss.

6. it should good moisture resistance.

7. Its colour should not fade with the passage of time.

 

BASES

The pigments commonly used as the principal constituents for forming the body of various types of paints are briefly given below:

White lead: This is perhaps the cheapest pigment and is thus extensively used for ordinary painting works. It is sold both in powder form as well as in the form of a stiff paste made by mixing it with linseed oil. It has good binding and spreading powder. It is very poisonous and is blackened when subjected to an atmosphere contaminated with sulphur compounds. Paints with white lead base can be easily tined. It is not recommended for painting of iron works as it does not check rusting of iron. White lead paints are best suited for wood work.

Red lead: It is an oxide of lead, bright red in colour and is usually sold in powder form or in the form of paste made by grinding it with linseed oil. Red lead mixed with linseed oil is considered to be the best primer both for wooden surface as well as structural steel work.

Zinc Oxide:  It is a fine white zinc powder which is available both in dry form as well as in the form of paste made by mixing in with linseed oil. This pigment is used as a base for all the zinc paints. Zinc white mixed with linseed oil forms a white paint, which has a good hiding and spreading powder. It is not effected by sulphur compounds and is not poisonous. It forms a costly paint, less workable and less durable than the white lead paints.

Iron Oxide: It is a pigment produced from haematite ore. The pigment is obtained by grinding and levigating the red or brown haematite. When mixed with vehicle oil, it forms a cheap and durable paint, which is exclusively used for the priming coat on the iron or structural steel.

VEHICLE

The vehicles commonly used in an oil paint are briefly described below:

Linseed oil: This is extensively used as a vehicle in oil paints. It is obtained by pressing crushed flax seeds. The drying of the oil takes place due to its oxidation when exposed to air. It may be used either in its raw state or refined state or in boiled form.

Raw Linseed oil: It is a vehicle, yellowish in colour, sweet in taste and has very little smell. It has inferior drying qualities and is generally used for inside painting work. It is normally used for delicate tints. The drying qualities of this vehicle can be improved by adding about one pound of white lead to every gallon of the oil and then allowing it to settle for a period of one week.

Double boiled Linseed oil: Its colour and transparency is exactly similar to that of raw linseed oil but it smells slightly different. It has quick drying qualities and is generally used for painting plastered surfaces.

Tury oil:  It is extracted by pressing the nuts of tury tree. It is a vehicle better than linseed oil and is largely used for making superior paints and varnishes. It stands well attack of alkalis.

 

THINNER

Turpentine is the most common thinner used in the preparation of an oil paint. Turpentine is a spirit obtained by distilling balsam, which is the resin or gum obtained from pine tree. Turpentine thus obtained is termed as spirit of turpentine, sap turpentine or oil of turpentine. Turpentine is an inflammable, volatile, colourless liquid, having a pungent smell. It is used in paints and varnishes to dilute them and to increase their properties. It is added in more quantity in the priming coat on wood work in order to increase ability of the paint to penetrate into the pores of the wood work, while in the outer or final coat is used in much less quantity.

COLOURING PIGMENTS

Colouring pigments are used to give the desired colour to the paint. In general, for white, black and very dark shades, the base itself is chosen to be a colour pigment. In case of light or bright colour, the desired shade is obtained by mixing pigment to white paint.

Black Pigments: Lamp black, vegetable black, ivory black

Brown Pigments: Raw umber, burnt umber, burnt sienna

Blue Pigments: Prussian blue, ultramarine blue, cobalt blue.

Red Pigments: Indian red, carmine, red lead, Tuscan red.

 

PREPARATION OF PAINTS

Mostly white lead oil paint forms the basis of all of light or bright colours. The base which is usually white lead is ground in linseed oil to the consistency of paste. Alternatively, the base may be obtained in the form of the paste directly from the market.

The base in the state of stiff paste is then softened or “broken up” by adding linseed oil in a small quantity at a time and then stirring the paste with wooden paddle. If a coloured paint is desired the proper colouring pigment is ground very fine and mixed with linseed oil to the consistency of paste separately. Drier, if used should also be separately ground in linseed oil and the paste mixture. The mixture is then strained through a fine canvas or a fine sieve.

The paint thus prepared, should be used and consumed at the earliest. If the prepared paint has to be kept unused for some time, it should be covered with a film of water to protect it from drying or skinning.

TYPES OF PAINTS:

Aluminium paints

Anti-corrosive paints

Asbestos paints

Bituminous paints

Bronze paints

Cellulose paints

Casein paints

Cement based paints

Oil paints

 

Aluminum paints: Aluminum paint is used for painting wood work and metal surfaces. Aluminum powder forms the base in this paint. In this paint the base is held in suspension and bound by, either quick drying spirit varnish, or slow drying oil varnish to suit the requirements of the surface to be painted. This paint is well established for its good weather resisting and water proofing qualities. It is highly heat reflective, resistant to corrosive action of sea water, and stands well the atmosphere contaminated with acidic fumes.

Anti-corrosive paints: This paint is generally used as a metal protection paint for preserving structural steel work against the adverse effect of fumes, acids, corrosive chemicals and the ravages of rough weather. Several types of anti-corrosive paints are manufactured these days. The pigments used in the various types of paints are dry lead, sublimed blue lead, zinc oxide and iron oxide, zinc dust, etc.

Asbestos paints: This type of paint is especially suitable for patch work or slopping leakage in metal roofs. It is also used for painting gutters, spouts flashings, etc. in order to prevent them from rusting. Asbestos or fibrous coating is sometimes used as damp proof cover for the outer face of the basement walls.

Bituminous paints: Bituminous paints are alkali resistant and are chiefly used for painting exterior brick work, and plastered surfaces. They are also used for water proofing and protection of iron and steel and are commonly applied on iron water mains and structural steel work under water and on fabricated iron and steel products. This type of paint is obtained in black colour but its colour can be modified by incorporating certain pigments like red oxide etc. these paints, however, deteriorate when exposed to the direct rays of the Sun.

Bronze paints: This type of paint is often used for painting interior or exterior metallic surface. On account of its high reflective property, it is commonly applied on radiators. Aluminium powder or copper powder are pigments commonly used in this paint. The vehicle used in the paint is usually nitrocellulose lacquer.

Cellulose paints: This type of paint is made from celluloid sheets and amyl-acetate substitutes. For making a superior type of paint, Nitro-cotton is used. It dries very quickly and possess the additional advantages of hardness, flexibility, and smoothness. It can be cleaned easily and it remains unaffected by hot water, smoky or acidic atmosphere and stands well the water and tear and ravages of rough weather.

Casein paints: Casein is a protein substance extracted from milk curd which is mixed up with a base consisting of white pigment like whiting, titanium, lithopone etc. to from the paint which is usually available in powder or pasty form. On account of its high opacity, the paint can be applied on new plaster work without any danger of scaling or alkali burning. The paint can be tinted in any desired shade of colour. It is usually applied on walls, ceiling, wall boards, cement block construction etc. to enhance the appearance of the surface.

Cement based paints: This is a type of water paint in which white or coloured pigment and cement forms the base. No oil or other organic matter is used in making this paint. This type of paint is available in packed powdered form under different trade names such as snowcem etc. This paint can be made by adding paint powder to water to obtain thick paste and thereafter diluting the paste with water to brush able consistency.

For new works, cement paint is applied in three coats whereas for old works one or at the most two coats may be sufficient. In any case, the second coat should be applied only after the first coat has set for 24 hours.

This paint is applied to exposed or plastered brick masonry and concrete work. On drying it forms a decorative, strong, durable and water resistant film surface.

Oil paints: This type of can be used for almost all surfaces such as wooden, masonry, metal etc. Oil paint basically consists of two main components viz. a base and a vehicle. Oil paints are manufactured in different shades and grades. They possess all the characteristics of good paint and as such are very common in use.

 

PROCESS OF PAINTING DIFFERENT SURFACES

Process of painting on new Woodwork:

The correct preparation of surface plays an important role in preserving the properties and life of the paint. The process of painting on new wood work can be divided into the following different stages:

1.Preparation of surface

2. Knotting

3. Priming

4. Stopping

5. Undercoating

6. Finishing coat

 

1.Preparation of surface Wood work to be painted must be properly seasoned, clean, dry and free from dust. The surface should be smoothened by rubbing it with a fine grade sand paper or glass paper used obliquely across the grains and rendered free from grease.

 2. Knotting Knots exude resin. Knotting is the process of sealing the knots by suitable means so that the resin from the knots may not destroy the paint film by way of cracking, peeling or brown discoloration.

3. Priming This consists in applying first coat or the priming coat on the surface to fill the pores of wood by penetrating the primer inside the wood. The main function of the priming coat or the primer is to serve as the foundation for the subsequent coats. Primers have definite functions to perform and their choice depends on the material being used and hardness or condition of wooden surface to be coated.

4. Stopping This consists in filling up all nail holes, cracks, open joints, dents and other such defects with the putty. Stopping is done soon after the priming coat is dry. Before filling putty, the primed surface is rubbed down with pumice stone or glass paper. After the putty has dried the surface is once again rubbed with glass paper or pumice to level the same. It should be coloured to match the shade of the finished coat.

5. Undercoating After the primary coat is dry, second coat or under coatings are applied on the primed surface. The colour of the under coat should approximately be of the same shade as that of the desired finish. It should be a thin opaque film, free from brush marks. Two or more under-coatings are sometimes necessary to achieve the object. For good result, the dry coating is rubbed down with pumice stone or glass paper and cleaned before applying the succeeding coats.

6. Finishing coat This is the last coat applied on the surface after the under-coat is properly dry. This coat is applied very carefully in a workman like manner, so that the finished surface is free from thin patches and brush marks.

 PAINTING OLD WOOD WORK

In case the old paint is in good condition but dirty and its removal is not considered necessary, the surface should be cleaned of all dirt and grease by washing it with lime and water. The cleaned surface is rubbed with pumice stone and the holes and cracks, if any are filled with glazier’s putty or wood putty.

If the old painted surface is in bad condition and the paint has badly blistered and flaked, it should be completely removed by use of a blow lamp or one of the patent paint removers. Paint remover should be in places where removing the old paint with blow lamp is not considered desirable.

Old paint can also be removed by applying caustic soda solution, on the surface and then stripping it with a sharp instrument. After removing the old paint, the cleaned surface is given two or three coats of the paint to obtained the desired finish.

PAINTING OLD DAMP WALLS

Take a mixture consisting of 10 litres of paraffin, 8 litres of benzoline and 6 kg. of pale resin in a vessel and shake them well, so that they get completely dissolved. Add 10 kg. of whiting to the mixture and grind it well. The paint thus formed may be applied in one or more coats on damp walls in the usual manner. On drying, it will form a dry hard film on the surface painted.

SPRAY PAINTING

Painting with the spray gun is considered to be a highly developed and efficient method of applying all types of protective coatings. It results, in rapid execution of work. There is also economy in labour and the consumption of material as only two coats of spray are considered sufficient to obtained the desired finish.

The paint is put into container and forced by air pressure through a hose to a metal gun. The gun is provided with a spray nozzle and a hose conveying compressed air.

In operating to spray gun, care should be taken to see that the spray is at right angles to the surface and at all times, the gun is kept at the same distance from the surface to be painted. This distance may vary from 15 to 20 cm. Spray painting should, however, be done only under dry condition.