12

SURFACE FINISHING MATERIALS

12.1 INTRODUCTION

Apart from protecting various building units from the weathering action of the atmosphere, the main objective of surface finishing materials is to provide a decorative finish to obtain a clean, colourful and pleasing surface.

Surface finishing materials are paints, varnishes, distempers and white/colour washing. The surfaces may be plastered wall surfaces, ceilings, wooden surfaces, metallic surfaces, etc. These surface finishing materials have to provide a hygienic surface and present a healthy surrounding to live in.

Paints are primarily used for woods, walls and ceilings, and for metal works of windows. Varnishes are preferred for woodworks and sometimes for walls.

Distempers and white/colour washing are used for walls. Different varieties of distempers are available in the market.

Apart from the above surface finish materials, other materials used are wallpaper, wall tiles, coal tar, waxing, etc.

This chapter discusses the above aspects.

12.2 PAINTS

Paint is mainly composed of two ingredients, viz., a base which is a solid material and a liquid called a vehicle. The vehicle carries the solid matter, distributes it evenly and enables the solid matter to adhere to the surface.

12.2.1 Functions of Paints

Irrespective of the type of paint, in general, the functions of paints are as follows:

1. It has to protect the surface from the weathering effects of atmosphere such as sun, wind, other liquids, fumes, etc.
2. It has to prevent corrosion of metal bases and decay of wooden surfaces.
3. It has to provide a smooth surface for easy cleaning.
4. It should provide the surface good aesthetic appearance and a hygienically sound surface.

12.2.2 Constituents of an Oil Paint

Metals and wooden surfaces are generally painted by oil paints. Sometimes walls are also painted by oil paints. Thus, it is worth discussing the constituents of an oil paint. An oil paint is made up of six main constituents, viz., base, inert filler, colouring pigment, vehicle, thinner and drier.

1. Base

The base forms the chief ingredient of a paint. The most important purpose of adding a base to the paint is to make an opaque coating so as to hide the surface to be painted and to reduce shrinkage cracks. The bases that are commonly used for the paints are white lead, red lead, oxide of zinc, oxide of iron, titanium white, etc.

2. Inert Filler

It is a cheap pigment added to a paint to reduce its cost. Further, it modifies the weight of the paint and makes it more durable. Commonly used inert fillers, also called as extenders, are barium sulphate, lithophone, silicate of magnesia or alumina, gypsum, etc.

3. Colouring Pigments

It is a white or coloured pigment added to the paint to get the desired colour of the paint.

4. Vehicle

Vehicle acts as a binder for various pigments, viz., bases, extender and colouring pigment. Vehicles are required for two purposes, mainly:

1. To make it possible to spread the paint as a thin layer on the surface evenly and uniformly.
2. To provide a binder for the ingredients of a paint such that the paint sticks to or adheres to the surface.

Vehicles that are commonly used are: linseed oil, tung oil, poppy oil, nut oil, etc.

5. Thinner

It is also known as solvent. It is a liquid which thins the consistency of the paint and evaporates after the paint film has been applied. It increases the workability of the paint. The commonly used solvents are: turpentine, pure oils, petroleum spirit and highly solvent naphtha.

6. Drier

It is a material used in small quantities for accelerating the drying of paint film. It is a metallic compound that acts as a catalyst for the oxidation and polymerization of the vehicle used in the paint. The commonly used driers are: litharge, lead acetate, manganese dioxide and cobalt. In an oil paint only 10% (by volume) of the drier should be used. The use of excess drier leads to flaking.

12.2.3 Characteristics of a Good Paint

An ideal paint should possess the following qualities:

1. The consistency of the paint should be adequately workable.
2. It should be capable of being spread across a wide area and cover the specific area with the minimum quantity of paint.
3. The thickness of the paint film should be enough for good protection and decoration of the surface.
4. It should dry within a reasonable time and not too rapidly.
5. The dried surface should withstand adverse weather conditions and should have a long life.
6. It should have adequate resistance to moisture, cracking and flaking.
7. It should be attractive as well as pleasing in appearance.
8. With time the colour should not fade.
9. During the application of paint it should not harm the health of the workers.
10. It should be fairly cheap and economical.

12.2.4 Types of Paints

Various types of paints are discussed below:

1. Oil Paint

The various constituents of an oil paint are discussed in Section 12.2.4. These paints are self-priming and in general do not need any special primer or undercoat. When it is used for general decoration purposes, it is a common practice to apply at least three coats of varying compositions, i.e., primers, undercoats and finishing coats on the unpainted surfaces.

2. Aluminium Paint

Finely ground aluminium is suspended in either quick-drying spirit varnish or slow-drying oil varnish as per the requirement. After painting, the spirit evaporates and a thin metal film of aluminium is formed on the surface. Aluminium paint has several advantages. It is widely used for painting gas tankers, hot water pipes, radiators, etc.

3. Cement Paint

The term cement paint is applied to paints which are based on white cement with a pigment, a filler and an accelerator. It is available in a dry powder form. A variety of shades are available and are water-proof and durable. It is mixed with water immediately before its application. Cement paints are ideal for rough surfaces because its adhesive power is poor on smooth surfaces.

Two coats have to be applied. Before applying the first coat the surface is wetted. The second coat is applied not less than 24 hours after the first coat. To obtain best results, the surface has to be kept wet for about two days after the final coat. However, the cement paint is not recommended for regions under sub-zero temperatures.

4. Anticorrosive Paint

It primarily consists of oil and a strong drier. Very fine sand is mixed with a pigment and added to the paint. The pigment may be chromium oxide, lead, red lead or zinc chromate. The appearance of the paint is black and has a long life. It is comparatively cheap.

5. Emulsion Paint

It contains binding materials such as polyvinyl acetate, synthetic resins, etc., and it is easy to apply. It dries quickly and the colour of the paint is retained for a long period. The surface of the paint is tough and can be cleaned by washing with water.

Emulsion painting can be carried out either by a brush or sprayed using a gun. Two coats are needed for a long life. In general, a smooth surface is needed to apply emulsion paint.

6. Enamel Paint

It contains white lead or zinc white, oil, petroleum spirit and resinous matter, which are available in different colours. It forms a hard and durable surface but dries slowly. The surface painted by enamel paint is not affected by acids, alkalies, fumes of gases, steam, water, etc. This is quite suitable both for internal and external walls. To make the appearance look better, it is recommended to apply a coat of titanium white in pale linseed oil before applying enamel paint.

7. Luminous Paint

This paint contains calcium sulphide with varnish. The surfaces painted by this paint shines like radium dials after the source of light has been cut off. This paint should be used only on surfaces that are free from corrosion or any other lead paint.

8. Cellulose Paint

This is a special type of paint prepared from nitro-cotton, celluloid sheets, photographic films, etc. It hardens on evaporation of a thinning agent and due to oxidation. Although it is costly, it presents a flexible, hard and smooth surface. The surface coated with this paint can withstand adverse weather conditions and can be washed and easily cleaned.

9. Asbestos Paint

This is a peculiar type of paint, and it is applied on the surfaces that are exposed to acidic gases and steam.

10. Plastic Paint

This type of paint is also called plastic emulsion paint and is available in the market under different trade names. The paint is composed of plastic compounds such as vinyl acetate and acrylate. This paint has a pleasing appearance, and it is attractive in colour. This is used in showrooms and auditoriums.

11. Bituminous Paint

This paint is obtained by dissolving asphalt or mineral pitches or vegetable bitumen in any type of oil or petroleum. This has a black appearance and is used to paint iron work under water.

12.3 VARNISHES

Varnish is a clear, pale solution of a resinous substance dissolved in either oil, turpentine or alcohol. The resinous substances are amber, common resin, copal, lac or shellac. The solution spread on the surface after drying forms a hard, transparent and glossy film on the varnished surface.

12.3.1 Functions of Varnishes

In general, varnish is applied on wooden surfaces of doors, windows, etc. to decorate the surface without hiding the beautiful grains of wood and at the same time to protect the surface from atmospheric effects. Sometimes painted surfaces are also varnished to enhance the appearance of the paint and also to increase the durability of the painted surface.

As the preparation of varnish is tough, readymade varnishes are used.

12.3.2 Constituents of Varnish

The three ingredients of a varnish are: resins or resinous substances, solvents and driers.

1. Resins

As stated earlier, the commonly used resins are copal, lac or shellac and resin. Copal is available from the earth at places where pine trees existed in the past. It is a hard substance in a variety of forms. Lac or shellac is obtained by the exudation of some insects. Resin is obtained from pine trees.

2. Solvents

Based on the type of resin, the type of solvent is decided. Table 12.1 shows the solvent for different resins.

3. Driers

To accelerate the process of drying, driers are added to the varnish. Common driers used in varnishes are litharge, white copper and lead acetate.

12.3.3 Properties of an Ideal Varnish

The properties of an ideal varnish are as follows:

1. It should always provide a glossy surface and be pleasing in appearance.
2. It should dry fast and provide a uniform finished surface.
3. When exposed to the atmosphere, the colour of the varnish should not fade.
4. The developed thin film on the surface should be tough, hard and durable.
5. During or after drying it should not show cracks or shrink.

12.3.4 Types of Varnishes

Based on the solvent used, varnishes may be classified as given below:

1. Oil Varnishes

Oil varnishes are prepared from the hardest resin or gums, such as amba, copal, etc., by heating and dissolving them in linseed oil with turpentine. Heat is added to increase the workability. Although it dries slowly, it is the hardest and most durable of all varnishes. In general, it can be used both for interior and exterior works. It is preferred for joinery and fitting purposes and for all outside works.

2. Turpentine Varnishes

These varnishes are prepared from soft resins such as gum dammar, mastic, common resins, etc., by dissolving them in pure spirits or turpentine. These varnishes are flexible, lighter in colour and quick in drying. Compared to oil varnishes they are weak.

3. Spirit Varnishes

These varnishes are also called lacquers. These are prepared from soft resins such as lac or shellac dissolved in methylated spirit. They are harder, dries quickly and brilliant in appearance. These are easily affected by weathering actions.

4. Water Varnishes

These varnishes are prepared using shellac, which is dissolved in hot water and mixed with an adequate quantity of ammonia or borax, potash or soda such that the shellac gets dissolved. Water varnishes are used to varnish wallpapers, maps, pictures, etc.

5. French Polish

This is a refined spirit varnish. It is prepared by dissolving 0.15 kg of black or light brown shellac in one litre of methylated spirit without heat. The polish is obtained by adding a suitable colour pigment. This polish dries out quickly within a few minutes. It gives a fine glossy surface. It is mostly used for superior wood works like furniture, hand rails, etc.

12.4 DISTEMPERS

12.4.1 Function of Distempers

Distempers are water paints consisting of whitening (i.e., powdered chalk), glue or casein as a binder and suitable colouring pigments. Distempers are used on plastered, cement concrete and on various wallboard surfaces. They are cheap, durable and are pleasing in appearance. They also safeguard the surfaces from adverse weather conditions.

12.4.2 Constituents of Distempers

Distemper comprises a base, a binder, a thinner and a pigment. Whitening or chalk forms the base, glue forms the binder, water forms the carrier or thinner and a colouring pigment.

Distempers are available in a powder form or a paste form. They are to be mixed with hot water before use. This is more or less used as a water paint. Here, whitening or chalk serves as the base instead of white lead and the water is used as a carrier instead of linseed oil.

12.4.3 Properties of Distempers

General properties of distempers are given below:

1. On drying the distemper shrinks which may lead to cracking and flaking. This is predominant if the surface is weak.
2. In general distemper coating is thicker and hence they are more brittle than other types of water paints.
3. They are less durable than oil paints.
4. The distemper layer is porous in nature and allows water vapour to pass through it.
5. They provide less workability.
6. It is not suitable in places where there is dampness.
7. They are available in light shades.

12.4.4 Types of Distempers

Different forms of distempers are discussed below:

1. White Distempers

This type of distemper is prepared by mixing only whitening (i.e., powdered chalk) and glue.

2. Coloured Distempers

In this type of distemper, the required colour pigment is added to the whitening before mixing with glue.

3. Oil Bound Distempers

A variety of oil paints are available in which drying oil is so treated that it mixes with water. Whenever required, such distempers are diluted or thinned with water. These distempers after allowing drying form a washable and durable surface.

4. Casein Paints

Casein is extracted from milk curds and acts as a binder. These paints are prepared by mixing a finely ground casein with a white base, normally slaked lime. This has high opacity. Thus, it is preferred for use on plastered surfaces, stuccos, fibre boards, cement blocks, etc.

12.5 WHITE AND COLOUR WASHING

White washing is the oldest method of surface finishing in use. The white-washing material is prepared from pure fat lime, which may be slaked at site. Slaking is carried out in a tub until the mixture shows a creamy consistency. The slaked lime is allowed to rest for 24–48 hours. The mixture is then strained through a coarse cloth. Three kilograms of gum boiled with 10 kilogram of rice are added to each cubic metre of the slaked lime.

The completed white-washed surface shall form an opaque coat of white colour. It also presents a smooth regular surface free from any powdery matter.

Colour washing is prepared by the addition of the necessary pigment to the pure slaked fat lime and mixed thoroughly. Then it is screened through a clean and fine cloth. During the time of application it is continuously stirred with a stick. To get uniformity, an adequate quantity should be mixed. Colour should not crack or come off readily on the fingers when rubbed.

12.6 MISCELLANEOUS SURFACE FINISHES

Apart from the surface finishing materials, the following methods are also used in specific cases:

12.6.1 Wallpapering

Wallpapers of a certain design are used for developing the aesthetic values of interior walls and ceilings. They may be exclusively of paper or combined with other materials. The papers used for papering are: pulp paper, satin paper or flock paper.

Pulp paper is the most commonly used type. Satin paper is easily maintained by cleaning but it is affected by dampness. The third type, flock paper gives a good aesthetic appearance but is prone to dust.

Varnished wallpaper is also available, which can be polished. There are certain wallpapers, which are washable for which oil paper may be used. Metal-coated wallpapers and wallpapers with sound-absorbing properties are also available.

12.6.2 Wall Tiling

Wall tiling is the process of lining or finishing the walls with special tiles up to a certain height. In general, the height varies from 60 to 120 cm above the floor level or in some cases up to the ceiling.

Particularly, wall tiling is done in kitchen, bathrooms, W.Cs, passages, fire places, staircase walls, boiler rooms, etc. Sometimes, it is also used on outer surfaces of decorative causes or to protect them from atmospheric influences.

Wall tiles are either of terracotta, china clay or marble available in different colours and designs.

12.6.3 Coal Tarring

For preservative purposes, coal tar is applied to wood work or iron work. The tarred surfaces can further be treated by varnishing or painting. The mixture is prepared by adding about 200 gm of unslaked lime for every litre of tar and then heated till it starts boiling. The hot mixture is thinned by adding 1/16^th litre of country spirit to each litre of tar.

12.6.4 Waxing or Wax Polishing

To improve the elegance and at the same time to protect undercoats, wax polishing is done on varnished surfaces. Wax polishing presents a highly pleasing lustre.

Wax polish is prepared by mixing bees-wax with linseed oil, turpentine and varnish in the ratio 2:1½:1:½, respectively, by weight. For preparing this, bees-wax is first melted or dissolved in linseed oil on low fire and then the mixture is cooled down slightly. Turpentine and varnish are then added to the mixture and then stirred well.

12.6.5 Wood Oiling

Woodwork not exposed to weather is generally provided with wood oiling as it is cheaper. Further, oiling of woodwork is done to increase the durability and also to improve the appearance of the surface. Linseed oil or sweet oil is used.

Linseed oiling consists of a mixture obtained by heating three parts of double-boiled linseed oil and one part of bees-wax to which one part of turpentine is added by weight. Sweet oiling consists of a mixture of equal parts of common vinegar, country sweet oil and spirits of turpentine. Sweet oiling mixture gives a darker effect than linseed oiling.

1. Paint is mainly composed of two ingredients, viz., a base which is a solid material and a liquid called a vehicle.
2. The vehicle carrying the solid matter distributes it evenly and enables the solid matter to adhere to the surface.
3. Constituents of an oil paint are base, inert filler, colouring pigment, vehicle, thinner and a drier.
4. The most important purpose of adding a base in a paint is to make an opaque coating so as to hide the surface to be painted and to reduce shrinkage cracks.
5. Inert filler is a cheap pigment added to a paint to reduce its cost.
6. Coloured pigment is added to the paint to obtain the desired colour of the paint.
7. Thinner, also known as a solvent, is a liquid which thins the consistency of the paint and evaporates after the paint film has been applied.
8. Drier is a material used in small quantities for accelerating the drying of the paint film.
9. In aluminium paint, finely ground aluminium is suspended in either quick-drying spirit varnish or slow-drying oil varnish as per the requirement.
10. The term cement paint is applied to paint which is based on white cement with a pigment, filler and an accelerator.
11. Anticorrosive paint primarily consists of oil and a strong drier. Very fine sand is mixed with a pigment and added to the paint.
12. Emulsion paint contains binding materials such as polyvinyl acetate, synthetic resins, etc., and it is easy to apply.
13. Enamel paint contains white lead or zinc white, oil, petroleum spirit and resinous matter.
14. Luminous paint contains calcium sulphide with varnish. The surface painted by this paint shines like a radium dial after the source of light has been cut off.
15. Cellulose paint is a special type of paint prepared from nitro-cotton, celluloid sheets, photographic films, etc.
16. Asbestos paint is applied to surfaces that are exposed to acidic gases and steam.
17. Plastic paint is composed of plastic compounds such as vinyl acetate and acrylate.
18. Bituminous paint is obtained by dissolving asphalt or mineral pitches or vegetable bitumen in any type of oil or petroleum.
19. Varnish is a clear, pale solution of a resinous substance dissolved in oil, turpentine or alcohol.
20. The three ingredients of varnish are resins or resinous substance, solvents and driers.
21. Commonly used resins are copal, lac or shellac and resin.
22. To accelerate the process of drying, driers are added to the varnish. Common driers used in varnishes are: litharge, white copper and lead acetate.
23. Oil varnishes are prepared from the hardest resin or gums such as amber, copal, etc., by heating and dissolving them in linseed oil with turpentine.
24. Turpentine varnishes are prepared from soft resins such as gums dammar, mastic, common resins, etc. by dissolving them in pure spirits or turpentine.
25. Spirit varnishes are called lacquers. These are prepared from soft resins such as lac or shellac dissolved in methylated spirits.
26. Water varnishes are prepared using shellac, which is dissolved in hot water and mixed with an adequate quantity of ammonia or borax, potash or soda such that shellac gets dissolved.
27. French polish is prepared by dissolving 0.15 kg black or light brown shellac in one litre of methylated spirit without heat.
28. Distempers are water paints consisting of whitening (i.e., powdered chalk), glue or casein as a binder and suitable colouring pigments.
29. A distemper comprises a base, a binder, a thinner and a pigment. Whitening or chalk forms the base, glue forms the binder, water forms the carrier or thinner and a colouring pigment.
30. White-washing material is prepared from pure fat lime which may be slaked at site. Slaking is carried out in a tub until the mixture shows a creamy consistency.
31. Colour washing is prepared by the addition of necessary pigments to the pure slaked fat lime and mixed thoroughly.

1. Explain the functions of a paint.
2. What are the ingredients of an oil paint? Explain.
3. List the characteristics of a good paint.
4. Enumerate the different types of paints.
5. What paints would you recommend for the following job, reason out your choice.

   (i) Steel bridge girder

   (ii) Steel Roof trunes

   (iii) Interior of a drawing room

   (iv) Walls of a cinema theatre

6. How do you select a solvent based on the resin to be used?
7. Explain the properties of an ideal varnish.
8. What are the different types of varnish?
9. What are the functions and essential ingredients of oil varnishes?
10. Why should distemper be preferred to white washing or colour washing?
11. Explain the object of distempering? Mention the ingredients and properties of distemper.
12. Where are wallpapers preferred?
13. What is waxing or wax polishing?
14. Enumerate the advantages of wall tiling.