Unit_5.en

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Paints and Varnishes Paints and Varnishes

UNIT

UNIT 5

5 P

PAINTS

AINTS AND

AND V

VARNISHE

ARNISHES

S

Structure

5.1 5.1 IntroductionIntroduction Objectives Objectives 5.2 5.2 PaintsPaints 5.2.1

5.2.1 Functions of PaintFunctions of Paint 5.2.2

5.2.2 Characteristics of an Ideal PaintCharacteristics of an Ideal Paint 5.2.3

5.2.3 Constituents of an Oil Paint or Oil Borne PaintConstituents of an Oil Paint or Oil Borne Paint 5.2.4

5.2.4 Types of PaintsTypes of Paints 5.2.5

5.2.5 Painting ProcessesPainting Processes 5.2.6

5.2.6 Painting on Plastered SurfacePainting on Plastered Surface 5.2.7

5.2.7 Painting on Concrete SurfacePainting on Concrete Surface 5.2.8

5.2.8 Defects in PaintingDefects in Painting 5.2.9

5.2.9 Failure of PaintsFailure of Paints

5.3

5.3 DistemperingDistempering

5.3.1

5.3.1 Composition of DistempersComposition of Distempers 5.3.2

5.3.2 Process of DistemperingProcess of Distempering 5.3.3

5.3.3 Properties of DistempersProperties of Distempers

5.4

5.4 VarnishesVarnishes

5.4.1

5.4.1 Functions of VarnishFunctions of Varnish 5.4.2

5.4.2 Properties of Good VarnishProperties of Good Varnish 5.4.3

5.4.3 Constituents of VarnishConstituents of Varnish 5.4.4

5.4.4 Types of VarnishTypes of Varnish 5.4.5

5.4.5 Process of VarnishingProcess of Varnishing

5.5

5.5 SummarySummary 5.6

5.6 Answers to SAQsAnswers to SAQs

5.1 INTRODUCTION

The paints, distempers and varnishes are provided as a part of the final treatment The paints, distempers and varnishes are provided as a part of the final treatment to all the surfaces of walls, ceilings, floors, wood work etc., both internally and to all the surfaces of walls, ceilings, floors, wood work etc., both internally and externally. Some more forms of finishes/treatments are also used depending upon externally. Some more forms of finishes/treatments are also used depending upon requirement. These building treatments perform two major functions:

requirement. These building treatments perform two major functions: (i)

(i) They provide a protective coating to the surfaces. This helps inThey provide a protective coating to the surfaces. This helps in preserving and protecting the materials used in the building preserving and protecting the materials used in the building

construction from environmental effects like heat, frost and rain construction from environmental effects like heat, frost and rain water.

water. (ii)

(ii) They provide decorative finish or treatment which adds to theThey provide decorative finish or treatment which adds to the aesthetic appearance of the surfaces and the building.

aesthetic appearance of the surfaces and the building.

In this unit, our emphasis will be on paints, distempers and varnishes and we will In this unit, our emphasis will be on paints, distempers and varnishes and we will be studying their functions, characteristics, types, constituents a

be studying their functions, characteristics, types, constituents a nd process ofnd process of application.

application.

Objectives

After studying this unit, you should be able to After studying this unit, you should be able to

•

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Engineering Materials

Engineering Materials _•_• _{describe the properties of good paints, varnishes and distempering,}_{describe the properties of good paints, varnishes and distempering,}

•

• know the constituents of paints, varnishes and distempering,know the constituents of paints, varnishes and distempering, •

• describe the process of painting, varnishing and distempering, anddescribe the process of painting, varnishing and distempering, and •

• explain the importance of their use.explain the importance of their use.

5.2 PAINTS

Paints are used to protect metals, timber or plastered surfaces from the corrosive Paints are used to protect metals, timber or plastered surfaces from the corrosive effects of weather, heat, moisture or gases etc. and also to improve their

effects of weather, heat, moisture or gases etc. and also to improve their appearance.

appearance.

5.2.1 5.2.1 Functions

Functions of

of Paint

Paint

Paint performs following functions : Paint performs following functions :

(i)

(i) It protects wood from decaying.It protects wood from decaying. (ii)

(ii) It prevents corrosion of metals.It prevents corrosion of metals. (iii)

(iii) It renders surface hygienically safe and clean.It renders surface hygienically safe and clean. (iv)

(iv) It gives decorative and attractive appearance to the surface.It gives decorative and attractive appearance to the surface. (v)

(v) It also protects the surface from harmful effects of atmosphericIt also protects the surface from harmful effects of atmospheric agencies.

agencies.

5.2.2 5.2.2 Characteristics

Characteristics of an

of an Ideal P

Ideal Paint

aint

An ideal paint should have the following characteristics : An ideal paint should have the following characteristics :

(i)

(i) The paint should be cheap.The paint should be cheap. (ii)

(ii) It should be easy and harmless to the user.It should be easy and harmless to the user. (iii)

(iii) It should retain its original colour for a long time.It should retain its original colour for a long time. (iv)

(iv) It should be able to cover maximum area of the surface with minimumIt should be able to cover maximum area of the surface with minimum quantities.

quantities. (v)

(v) The painted surface should dry neither too slowly nor too rapidly.The painted surface should dry neither too slowly nor too rapidly. (vi)

(vi) When applied, the paint should form a thin uniform film on paintedWhen applied, the paint should form a thin uniform film on painted surface.

surface. (vii)

(vii) The paint should form a hard and durable coat on the painted surface.The paint should form a hard and durable coat on the painted surface. (viii)

(viii) The paint should not peel off from painted surface.The paint should not peel off from painted surface. (ix)

(ix) It should be good fire and moisture resistant.It should be good fire and moisture resistant. (x)

(x) The painted surface should not show any cracks.The painted surface should not show any cracks. (xi)

(xi) The painted surface should possess attractive and decorative pleasingThe painted surface should possess attractive and decorative pleasing appearance.

appearance. (xii)

(xii) Atmospheric agencies should not be able to affect the painted surface.Atmospheric agencies should not be able to affect the painted surface.

5.2.3 5.2.3 Constituents

Constituents of an Oil

of an Oil Paint or Oi

Paint or Oil Borne Paints

l Borne Paints

An oil paint essentially consists of the following ingredients : An oil paint essentially consists of the following ingredients :

(i)

(i) A baseA base (ii)

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(iii)

(iii) A vehicle or carrierA vehicle or carrier (iv)

(iv) A drierA drier (v)

(v) A solvent or thinnerA solvent or thinner (vi)

(vi) A colouring pigmentA colouring pigment Base

Base

It provides body to the paint and on it depends upon the nature of paints to a It provides body to the paint and on it depends upon the nature of paints to a great extent.

great extent. A base in A base in general should possess the general should possess the following properties :following properties : (i)

(i) It It is is the the solid solid matter matter forming forming the the main main body body of of the the paint.paint. (ii)

(ii) It It makes makes the the paint paint film film harder harder and and more more resistant to resistant to abrasion.abrasion. (iii)

(iii) It It reduces reduces shrinkage shrinkage cracks cracks formed formed on on drying.drying. (iv)

(iv) It forms It forms an opaquan opaque layer e layer to obscure to obscure the surface the surface of material of material to beto be painted.

painted.

White lead, Red lead, Zinc oxide, Iron oxide, and metallic powders such as White lead, Red lead, Zinc oxide, Iron oxide, and metallic powders such as Aluminium, Copper and Bronze etc. are the commonly used bases.

Aluminium, Copper and Bronze etc. are the commonly used bases. An Inert Extender or Filter

An Inert Extender or Filter

They are added in the paint to reduce the cost and also to modify some of They are added in the paint to reduce the cost and also to modify some of the properties of the paints. They reduce weight of the paint and render the properties of the paints. They reduce weight of the paint and render paint more durable. They should not be used in excess amoun

paint more durable. They should not be used in excess amount as otherwiset as otherwise paint may loose its original character and may become weak.

paint may loose its original character and may become weak.

Barium sulphate silica, lithophone, whiting, charcoal, gypsum silicate of Barium sulphate silica, lithophone, whiting, charcoal, gypsum silicate of magnesia or alumina etc. are the usual inert extenders.

magnesia or alumina etc. are the usual inert extenders. Vehicles or Carriers

Vehicles or Carriers

They are liquid substances which hold solid ingredients of the paint. In They are liquid substances which hold solid ingredients of the paint. In general vehicles or carriers possess the following properties :

general vehicles or carriers possess the following properties : (i)

(i) It It is is an an oily oily liquid liquid in in which which the the base base and and pigment pigment are are soluble.soluble. (ii)

(ii) It It facilitates the facilitates the paint paint to to be be conveniently conveniently spread spread evenly evenly over over thethe surface by means of a brush.

surface by means of a brush. (iii)

(iii) It acts It acts as a as a binder for binder for the base the base and causes and causes it to it to stick to stick to the surface.the surface. (iv)

(iv) On dOn drying, it rying, it forms a forms a tough and tough and an elastic an elastic film. Oils film. Oils most commost commonlymonly used as vehicles are linseed oil, poppy oil, nut oil and tung oil.

used as vehicles are linseed oil, poppy oil, nut oil and tung oil. Driers

Driers

These are metallic compounds which when added to the paint in small These are metallic compounds which when added to the paint in small quantities accelerate the process of drying of the paint. Driers have a quantities accelerate the process of drying of the paint. Driers have a

tendency to affect the colour of the paint and also to destroy the elasticity of tendency to affect the colour of the paint and also to destroy the elasticity of the paint. Hence, they should not be used in excess amount. They are not the paint. Hence, they should not be used in excess amount. They are not used at all in final finishing coat of the paint. Driers should not be used in a used at all in final finishing coat of the paint. Driers should not be used in a paint that dries well.

paint that dries well.

Litharge, manganese dioxide, lead acetate and cobalt are the usual driers, Litharge, manganese dioxide, lead acetate and cobalt are the usual driers, out of which litharge is most commonly used.

out of which litharge is most commonly used. Solvents or Thinners

Solvents or Thinners

A liquid thinner is added to the prepared paints to increase their fluidity to A liquid thinner is added to the prepared paints to increase their fluidity to the desired consistency so as to make them work more smoothly and also to the desired consistency so as to make them work more smoothly and also to help penetration of porous surfaces. It evaporates after the paint has been help penetration of porous surfaces. It evaporates after the paint has been

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Engineering Materials _{applied to the surface. It also helps the paint in its penetration into the}_{applied to the surface. It also helps the paint in its penetration into the}

surface to be painted. surface to be painted.

Turpentine oil, petroleum spirits and naphtha are mostly used as solvents or Turpentine oil, petroleum spirits and naphtha are mostly used as solvents or thinners.

thinners.

Colouring Pigments Colouring Pigments

These are colouring agents which are used to develop desired shade of the These are colouring agents which are used to develop desired shade of the paint. For white, black and other very dark shades, the base of the paint is paint. For white, black and other very dark shades, the base of the paint is

chosen in such a way that, it will develop the colour of the paint through chosen in such a way that, it will develop the colour of the paint through base itself. In case of other shades, colouring pigments of desired shade are base itself. In case of other shades, colouring pigments of desired shade are

mixed with the paint. Colouring pigments may be divided into five mixed with the paint. Colouring pigments may be divided into five divisions.

divisions. (i)

(i) PrecipitatesPrecipitates (ii)

(ii) Natural earth Natural earth (iii)

(iii) Calcined coloursCalcined colours (iv)

(iv) Lake coloursLake colours (v)

(v) Metallic powdersMetallic powders

Various colouring pigments to develop a particular colour are as follows : Various colouring pigments to develop a particular colour are as follows : (i)

(i) BlueBlue (ii)

(ii) BrownBrown (iii)

(iii) BlackBlack (iv)

(iv) GreenGreen (v)

(v) YellowYellow (vi)

(vi) RedRed

5.2.4 5.2.4 Types

Types of

of Paints

Paints

The paints are of following types : The paints are of following types :

(i)

(i) Aluminium PaintAluminium Paint (ii)

(ii) Anti-Corrosive paintsAnti-Corrosive paints (iii)

(iii) Asbestos paintsAsbestos paints (iv)

(iv) Bituminous paintBituminous paint (v)

(v) Bronze paintsBronze paints (vi)

(vi) Cellulose paintCellulose paint (vii)

(vii) Casein paintCasein paint (viii)

(viii) Cement paintCement paint (ix)

(ix) Enamel paintEnamel paint (x)

(x) Emulsion paintEmulsion paint (xi)

(xi) Graphite paintGraphite paint (xii)

(xii) Plastic paintsPlastic paints (xiii)

(xiii) Silicate paintSilicate paint (xiv)

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(xv)

(xv) Inodorous paintInodorous paint (xvi)

(xvi) Rubber paintRubber paint

Details of each of these paints are described below : Details of each of these paints are described below : Aluminium Paint

Aluminium Paint

The paint is prepared by holding very finely ground aluminium in The paint is prepared by holding very finely ground aluminium in

suspension either in quick drying spirit varnish or slow drying oil varnish as suspension either in quick drying spirit varnish or slow drying oil varnish as per the requirements of the surface to be painted. The suspension liquid is per the requirements of the surface to be painted. The suspension liquid is spirit or oil, evaporates and a thin metallic film of aluminium is left on the spirit or oil, evaporates and a thin metallic film of aluminium is left on the surface. This paint is used for painting wood work and metal surfaces. It is surface. This paint is used for painting wood work and metal surfaces. It is widely used for painting hot water pipes, gas tanks, marine piers, oil storage widely used for painting hot water pipes, gas tanks, marine piers, oil storage tanks, radiators, etc.

tanks, radiators, etc. Anti-corrosive Paint Anti-corrosive Paint

These paints are used mainly to protect the surface of metallic structural These paints are used mainly to protect the surface of metallic structural steel work, against the negative effects of acids, corrosive chemicals fumes steel work, against the negative effects of acids, corrosive chemicals fumes etc. There are several paints which exhibit these properties. These paints etc. There are several paints which exhibit these properties. These paints essentially consist of the linseed oil, as vehicle and red lead, zinc oxide, essentially consist of the linseed oil, as vehicle and red lead, zinc oxide, iron oxide, zinc dust, zinc chromate etc. as their base. These paints are iron oxide, zinc dust, zinc chromate etc. as their base. These paints are cheap, durable and are usually black in colour.

cheap, durable and are usually black in colour. Asbestos Paint

Asbestos Paint

This paint is used for stopping leakage of metal roofs and painting gutters, This paint is used for stopping leakage of metal roofs and painting gutters, spouts, flashings etc. to prevent their rusting. The paint is also used as damp spouts, flashings etc. to prevent their rusting. The paint is also used as damp proof coat to cover the outer face of the basement walls. This paint can proof coat to cover the outer face of the basement walls. This paint can

withstand the effects of acidic gases and steam. withstand the effects of acidic gases and steam. Bituminous Paint

Bituminous Paint

This paint consists of asphalt, bitumen or pitches, dissolves in any type of This paint consists of asphalt, bitumen or pitches, dissolves in any type of oil or petroleum. The paint is always black in colour but its colour can be oil or petroleum. The paint is always black in colour but its colour can be modified by mixing certain pigment like red oxide etc. in it. The paint is modified by mixing certain pigment like red oxide etc. in it. The paint is used mostly for painting iron-works under water. These paints deteriorate used mostly for painting iron-works under water. These paints deteriorate when exposed to direct sun. It is also used for water proofing.

when exposed to direct sun. It is also used for water proofing. Bronze Paint

Bronze Paint

These paints are prepared by disbursing aluminium bronze or copper bronze These paints are prepared by disbursing aluminium bronze or copper bronze in nitro-cellulose lacquer as vehicle. They produce a very reflective type of in nitro-cellulose lacquer as vehicle. They produce a very reflective type of surface and hence very useful for being applied on radiators. These paints surface and hence very useful for being applied on radiators. These paints are equally effective for painting interior or exterior metallic surfaces. are equally effective for painting interior or exterior metallic surfaces. Cellulose Paint

Cellulose Paint

This type of paint is prepared from cellulose sheets, nitro-cotton and This type of paint is prepared from cellulose sheets, nitro-cotton and photographic films. This paint dries very quickly and provides a flexible, photographic films. This paint dries very quickly and provides a flexible,

hard and smooth surface. The paint does not harden by oxidation but by hard and smooth surface. The paint does not harden by oxidation but by evaporation of thinning agent. The surface of the paint can be easily washed evaporation of thinning agent. The surface of the paint can be easily washed and cleaned. It remains unaffected by hot water, smoky or acidic

and cleaned. It remains unaffected by hot water, smoky or acidic atmosphere. This paint is used for painting cars, aeroplanes etc. atmosphere. This paint is used for painting cars, aeroplanes etc. Casein Paint

Casein Paint

Casein is a product extracted from milk curd. Casein paint when mixed with Casein is a product extracted from milk curd. Casein paint when mixed with base like whiting, titanium, lithophone, etc. forms the paint which is usually base like whiting, titanium, lithophone, etc. forms the paint which is usually

available in powder or paste form. This paint has high capacity and can be available in powder or paste form. This paint has high capacity and can be applied on new plaster work. It is usually used on walls, ceilings wall applied on new plaster work. It is usually used on walls, ceilings wall

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Engineering Materials _{boards, cements block construction etc. to increase the appearance of the}_{boards, cements block construction etc. to increase the appearance of the}

surface. surface. Cement Paint Cement Paint

This paint is available in powder form. It consists of white or coloured This paint is available in powder form. It consists of white or coloured cement as its base and water acts as a vehicle. No oil or varnish is added to cement as its base and water acts as a vehicle. No oil or varnish is added to it. This paint is available in variety of shades. It is durable and water-proof. it. This paint is available in variety of shades. It is durable and water-proof. This paint proves to be useful for surfaces which are damp at the time of This paint proves to be useful for surfaces which are damp at the time of painting and are also likely to remain damp after painting.

painting and are also likely to remain damp after painting. Enamel Paint

Enamel Paint

This paint is prepared by adding base like white lead or zinc white to a This paint is prepared by adding base like white lead or zinc white to a vehicle which is a varnish. To obtain the desired colour, colouring pigments vehicle which is a varnish. To obtain the desired colour, colouring pigments may also be added. This paint dries slowly and forms a hard, durable,

may also be added. This paint dries slowly and forms a hard, durable, smooth, glossy, solid thin film. Enamel paints can be used both for interior smooth, glossy, solid thin film. Enamel paints can be used both for interior as well as exterior painting.

as well as exterior painting. Emulsion Paint

Emulsion Paint

This paint consists of synthetic resin like polyvinyl acetate. It can be This paint consists of synthetic resin like polyvinyl acetate. It can be applied easily. It retains its colour for a very long time. The surface of the applied easily. It retains its colour for a very long time. The surface of the paint is tough and can be cleaned by washing with water. This paint has paint is tough and can be cleaned by washing with water. This paint has excellent resistance against action of alkali. It dries very quickly in about excellent resistance against action of alkali. It dries very quickly in about one to two hours.

one to two hours. Graphite Paint

Graphite Paint

It is black in colour. It is used over the surface which come in contact with It is black in colour. It is used over the surface which come in contact with ammonia, chlorine, sulphur gases, etc. It is very much used in under ground ammonia, chlorine, sulphur gases, etc. It is very much used in under ground railways.

railways. Plastic Paint Plastic Paint

This paint contains a variety of plastics in suspension and is available in the This paint contains a variety of plastics in suspension and is available in the market under different trade name. It is mostly used in show rooms, display market under different trade name. It is mostly used in show rooms, display rooms, and auditorium etc. It can be applied by spray or by brush.

rooms, and auditorium etc. It can be applied by spray or by brush. Silicate Paint

Silicate Paint

It is prepared by mixing calcium and finely ground silica with resinous It is prepared by mixing calcium and finely ground silica with resinous

materials. It forms a very hard and durable film on painted surface. It can be materials. It forms a very hard and durable film on painted surface. It can be directly applied on brick, concrete or plastered surface, but only after

directly applied on brick, concrete or plastered surface, but only after wetting them.

wetting them. Luminous Paint Luminous Paint

This paint is prepared by mixing calcium sulphide with varnish. This paint This paint is prepared by mixing calcium sulphide with varnish. This paint shines in darkness like radium dials of watches. This paint should be

shines in darkness like radium dials of watches. This paint should be applied on surface which have been rendered free from corrosion or lead applied on surface which have been rendered free from corrosion or lead paints in particular.

paints in particular. Inodorous Paint

Inodorous Paint

This paint consists of white lead or zinc white mixed with methylated spirit. This paint consists of white lead or zinc white mixed with methylated spirit. No turpentine is used in this paint. White lead or zinc white is ground in oil. No turpentine is used in this paint. White lead or zinc white is ground in oil.

Shellac with same quantity of linseed oil and castor oil is dissolved in Shellac with same quantity of linseed oil and castor oil is dissolved in methylated spirit and this mixture is mixed with lead or zinc white paste methylated spirit and this mixture is mixed with lead or zinc white paste prepared in linseed oil. This paint dries quickly, but is not durable.

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Rubber Paint Rubber Paint

This paint is prepared by treating rubber with chlorine gas (chlorinated This paint is prepared by treating rubber with chlorine gas (chlorinated rubber) and then dissolving it in suitable solvent. This paint can be used on rubber) and then dissolving it in suitable solvent. This paint can be used on new concrete and lime plastered surfaces. This paint dries quickly. It is little new concrete and lime plastered surfaces. This paint dries quickly. It is little affected by weather and sunlight. It is resistant against chemical actions, affected by weather and sunlight. It is resistant against chemical actions, water, etc.

water, etc.

5.2.5 5.2.5 Painting

Painting Processes

Processes

Application of paint to a surface either with a brush or by spraying is known as Application of paint to a surface either with a brush or by spraying is known as painting. The surface to be painted should be perfectly smooth, clean and dry. painting. The surface to be painted should be perfectly smooth, clean and dry. Presence of moisture between the paint and surface to be painted or between Presence of moisture between the paint and surface to be painted or between successive coats of paints causes blisters.

successive coats of paints causes blisters. Painting should Painting should as far as possible beas far as possible be carried out in dry weather.

carried out in dry weather.

Brush of only good quality, the hair of which do not come off while painting, Brush of only good quality, the hair of which do not come off while painting, should be used.

should be used.

The paint is applied on

The paint is applied on the surface in two, three or four the surface in two, three or four coats. coats. The first coat isThe first coat is known as priming

known as priming coat and last one as finishing coat. coat and last one as finishing coat. All the intervening coatsAll the intervening coats are known as under coats.

are known as under coats.

Prime coat forms a thin film which helps in adhesion of the paint with the surface. Prime coat forms a thin film which helps in adhesion of the paint with the surface. It also protects the surface from

It also protects the surface from weathering action. weathering action. Materials for priming coatMaterials for priming coat should be selected keeping in view the nature of the surface to be painted. should be selected keeping in view the nature of the surface to be painted. Under coats serve as foundation on

Under coats serve as foundation on to the finishing coat. to the finishing coat. These coats fill all theThese coats fill all the irregularities of the surface.

irregularities of the surface.

Finishing coat is lastly applied as per the requirements. Finishing coat is lastly applied as per the requirements.

5.2.6 5.2.6 Painting

Painting on

on Plastered

Plastered Surface

Surface

A plastered surface should be painted only after it has thoroughly dried, otherwise A plastered surface should be painted only after it has thoroughly dried, otherwise the paint would get sploit. The following factors should be kept in mind while the paint would get sploit. The following factors should be kept in mind while painting a plastered surface :

painting a plastered surface : (i)

(i) As far as possible fresh plastered surfaces should not be painted. AtAs far as possible fresh plastered surfaces should not be painted. At least 6 months to 12 months time should be given to the plastered least 6 months to 12 months time should be given to the plastered surface to dry completely.

surface to dry completely. (ii)

(ii) Fresh plaster is alkaline in nature, because lime is liberated during theFresh plaster is alkaline in nature, because lime is liberated during the hydration of cement. Oil based paints and distempers are prone to hydration of cement. Oil based paints and distempers are prone to alkali attack in the presence of moisture. Hence, if freshly plastered alkali attack in the presence of moisture. Hence, if freshly plastered surface is to be painted, an alkali resistant primer paint should be surface is to be painted, an alkali resistant primer paint should be applied or alternatively paints not containing any oil should be used. applied or alternatively paints not containing any oil should be used. Spots of plastered surface showing efflorescence should be brushed off. If spots Spots of plastered surface showing efflorescence should be brushed off. If spots appear again, they should again be brushed off and painting should be postponed appear again, they should again be brushed off and painting should be postponed till such spots ceases to appear.

till such spots ceases to appear.

In case of new plastered surfaces, a solution of one kilogram of zinc sulphate in In case of new plastered surfaces, a solution of one kilogram of zinc sulphate in two kilograms of water should be applied to the surface. When it has dried then a two kilograms of water should be applied to the surface. When it has dried then a coat of pure raw linseed oil is applied. It is followed by two coats of paint thinned coat of pure raw linseed oil is applied. It is followed by two coats of paint thinned with turpentine and a little varnish. Third coat consisting of white lead, linseed with turpentine and a little varnish. Third coat consisting of white lead, linseed oil, desired pigment and a little oil of turpentine is then applied. Finishing coat oil, desired pigment and a little oil of turpentine is then applied. Finishing coat may be the same as third coat but with a little more of turpentine oil.

may be the same as third coat but with a little more of turpentine oil.

However, these days paints are available in market that can be applied directly on However, these days paints are available in market that can be applied directly on newly plastered surfaces. These are known as cement paints.

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_5.2.7

_{5.2.7 Painting}

_{Painting on}

_{on Concrete}

_{Concrete Surfaces}

_Surfaces

For painting concrete surfaces, cement paints are used. They are available in For painting concrete surfaces, cement paints are used. They are available in powder form. They are used by mixing

powder form. They are used by mixing with water. Prepared paint should bewith water. Prepared paint should be consumed within 2 hrs or its preparation. Two coats should be applied at an consumed within 2 hrs or its preparation. Two coats should be applied at an interval of 24 hrs. The painted surface should be cured by sprinkling water at interval of 24 hrs. The painted surface should be cured by sprinkling water at intervals.

intervals.

5.2.8 5.2.8 Defects

Defects in

in Painting

Painting

The following defects may occur in painted surface : The following defects may occur in painted surface : Fading

Fading

The paint may lose some of its colour due to effects of sunrays on colouring The paint may lose some of its colour due to effects of sunrays on colouring pigments.

pigments. Flaking

Flaking

Due to poor adhesion, paint may peel off from the surface. Due to poor adhesion, paint may peel off from the surface. Grinning

Grinning

If the opacity of the final coat is insufficient, the back ground of the painted If the opacity of the final coat is insufficient, the back ground of the painted surface is clearly visible. This defect is known as grinning.

surface is clearly visible. This defect is known as grinning. Bloom

Bloom

Due to bad ventilation or defective paint, dull patches are developed on the Due to bad ventilation or defective paint, dull patches are developed on the painted surface.

painted surface. Flashing

Flashing

This is opposite of bloom. In this defect, glossy patches are developed on This is opposite of bloom. In this defect, glossy patches are developed on the painted surface. The reason of this defect may be cheap paint, weather the painted surface. The reason of this defect may be cheap paint, weather reaction or poor workmanship.

reaction or poor workmanship. Blistering

Blistering

This defect occurs due to trapped moisture behind the painted surface. This defect occurs due to trapped moisture behind the painted surface. Running

Running

This defect occurs when the surface to be painted is very smooth. In this This defect occurs when the surface to be painted is very smooth. In this defect, small areas of the surface are left uncovered with paint.

defect, small areas of the surface are left uncovered with paint. Sagging

Sagging

Thickness of painting should not be excessive. If too much thick coat of Thickness of painting should not be excessive. If too much thick coat of paint is applied, the defect is known as sagging.

paint is applied, the defect is known as sagging. Wrinkling

Wrinkling

This defect occurs in thickly painted surfaces. This defect occurs in thickly painted surfaces. Saponification

Saponification

Defect of formation of soap patches on the painted surface is known as Defect of formation of soap patches on the painted surface is known as saponification. This defect occurs due to chemical action of the alkalies. saponification. This defect occurs due to chemical action of the alkalies.

5.2.9 5.2.9 Failure

Failure of

of Paint

Paint

When paint applied on the surface does not perform its purposes, it is called When paint applied on the surface does not perform its purposes, it is called failure of the paint. Painting is an easy job but also has its own peculiarities. The failure of the paint. Painting is an easy job but also has its own peculiarities. The following are the main causes of failure of paint.

following are the main causes of failure of paint. Bad Workmanship

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Painters are generally in habit of thinning the paint too much so that he may Painters are generally in habit of thinning the paint too much so that he may save paint and labour both. This leads to bad workmanship and it is possible save paint and labour both. This leads to bad workmanship and it is possible that paint may be absent for portions of surface.

that paint may be absent for portions of surface. Wrong Choice of Paint

Wrong Choice of Paint

Choice of paint is done based upon climatic conditions, nature of surface to Choice of paint is done based upon climatic conditions, nature of surface to be painted and so many other factors affecting the performance of the paint. be painted and so many other factors affecting the performance of the paint.

Low quality paints are cheap but their durability is very poor. Low quality paints are cheap but their durability is very poor. Surface Penetration

Surface Penetration

If the surface to be painted has not been prepared well to receive the paint, If the surface to be painted has not been prepared well to receive the paint, it may lead to failure of the paint.

it may lead to failure of the paint. Moisture

Moisture

Leakage of moisture on any painted surface accelerates the process of Leakage of moisture on any painted surface accelerates the process of separating the paint layer from the surface.

separating the paint layer from the surface. Salts and Alkalies

Salts and Alkalies

The movement of moisture can also transport salts from either internal The movement of moisture can also transport salts from either internal volume of masonry or new deposits. Such salts and alkalies saponify the oil volume of masonry or new deposits. Such salts and alkalies saponify the oil paints.

paints.

Conditions for Painting Conditions for Painting

The painting should be done when atmospheric conditions are favourable. The painting should be done when atmospheric conditions are favourable. Dirt, dust and moisture must not get entrapped during the process of

Dirt, dust and moisture must not get entrapped during the process of painting.

painting.

SAQ 1

(a)

(a) Briefly describe the characteristics of an ideal paint.Briefly describe the characteristics of an ideal paint. (b)

(b) Explain the various defects which may develop in painting.Explain the various defects which may develop in painting. (c)

(c) Explain the method of painting on concrete surfaces.Explain the method of painting on concrete surfaces. (d)

(d) Describe the functions of each ingredient of an oil paint.Describe the functions of each ingredient of an oil paint. (e)

(e) Explain in brief the painting process.Explain in brief the painting process. (f)

(f) Describe the reasons of failure of paints.Describe the reasons of failure of paints.

5.3 DISTEMPERING

It is also a process of applying wash or coating like white washing or colour It is also a process of applying wash or coating like white washing or colour washing on the surface. Finished surfaces obtained by distempering are far washing on the surface. Finished surfaces obtained by distempering are far superior than those obtaind by white washing or colour washing. Distempers are superior than those obtaind by white washing or colour washing. Distempers are available in ready made form in the market under different trade names.

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_5.3.1

_{5.3.1 Composition}

_{Composition of}

_{of Distempers}

_Distempers

Any distemper consists of a

Any distemper consists of a basebase, a, a carriercarrier,, colouring agentcolouring agent, and size. Whiting, and size. Whiting (powdered chalk) is used as base and water as the carrier. Colouring agents or (powdered chalk) is used as base and water as the carrier. Colouring agents or pigments are added only, if specific shade is to be obtained. Glue is mostly used pigments are added only, if specific shade is to be obtained. Glue is mostly used

as size. as size.

Distempers may also be termed as a water paint, having whiting as base and water Distempers may also be termed as a water paint, having whiting as base and water as the carrier. Distempers are available in powder form or paste form. They are to as the carrier. Distempers are available in powder form or paste form. They are to be mixed with hot water before use. There is a variety of oil bound distempers be mixed with hot water before use. There is a variety of oil bound distempers

also, in which the drying oil is so treated that it mixes with water readily. also, in which the drying oil is so treated that it mixes with water readily.

Distempers are applied on the surface with the help of distemper brushes which Distempers are applied on the surface with the help of distemper brushes which are about 10 cm wide.

are about 10 cm wide.

5.3.2 5.3.2 Process

Process of

of Distempering

Distempering

Distempering a surface involves following operations : Distempering a surface involves following operations :

(i)

(i) Preparation of the surfacePreparation of the surface (ii)

(ii) Applying prime coatApplying prime coat (iii)

(iii) DistemperingDistempering Preparation of the Surface Preparation of the Surface

Surface to be distempered should be absolutely dry. Dampness in the Surface to be distempered should be absolutely dry. Dampness in the surface spoils the distemper coat. Holes, patches, cracks, efflorescence surface spoils the distemper coat. Holes, patches, cracks, efflorescence spots etc. should be thoroughly cleaned and filled with gypsum or lime spots etc. should be thoroughly cleaned and filled with gypsum or lime putty. If the surface is to be redistempered the old coating should be washed putty. If the surface is to be redistempered the old coating should be washed with water and allowed to dry completely. The surface in the last should be with water and allowed to dry completely. The surface in the last should be thoroughly rubbed with sand paper and cleaned.

thoroughly rubbed with sand paper and cleaned. Applying Prime Coat

Applying Prime Coat

After preparation of the surface, it should be primed by applying a coat of After preparation of the surface, it should be primed by applying a coat of whiting in water or only of milk. Priming coat helps in developing a good whiting in water or only of milk. Priming coat helps in developing a good bond of distemper with the surface. The priming coat should be allowed to bond of distemper with the surface. The priming coat should be allowed to

dry completely, before distemper coat is applied over it. dry completely, before distemper coat is applied over it. Distempering

Distempering

After having applied the priming coat, first coat of distemper is applied on After having applied the priming coat, first coat of distemper is applied on the surface. The first coat should be of a light tint and applied with great the surface. The first coat should be of a light tint and applied with great care. Second coat is applied after the first coat has dried and become hard. care. Second coat is applied after the first coat has dried and become hard. Distempering coats are applied with the help of broad stiff distemper Distempering coats are applied with the help of broad stiff distemper brushes. Now-a-days, distempers can be applied with the help of spray brushes. Now-a-days, distempers can be applied with the help of spray pistols also.

pistols also.

5.3.3 5.3.3 Properties

Properties of

of Distempers

Distempers

(i)

(i) Distempers generally shrink on drying. Hence, if the surface receivingDistempers generally shrink on drying. Hence, if the surface receiving distemper is weak, it may lead to cracking and flaking of the

distemper is weak, it may lead to cracking and flaking of the distempers.

distempers. (ii)

(ii) Distempers are available in powder form and also in paste form.Distempers are available in powder form and also in paste form. Powdered distempers are known as dry distempers, whereas paste Powdered distempers are known as dry distempers, whereas paste form distempers are known as oil bound distempers. Oil bound form distempers are known as oil bound distempers. Oil bound distempers are superior than dry distempers.

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(iii)

(iii) Coatings of distempers are comparatively thick and are more brittleCoatings of distempers are comparatively thick and are more brittle than other water paints.

than other water paints. (iv)

(iv) Distemper film is generally porous in nature and it allows waterDistemper film is generally porous in nature and it allows water vapour to pass through it. Hence it allows new walls to dry out vapour to pass through it. Hence it allows new walls to dry out without damaging the distemper film.

without damaging the distemper film. (v)

(v) They are less durable than oil paints.They are less durable than oil paints. (vi)

(vi) Distempers are generally light in colour and provide a good reflectiveDistempers are generally light in colour and provide a good reflective coating.

coating. (vii)

(vii) They can be applied on cement plastered surface, lime plasteredThey can be applied on cement plastered surface, lime plastered surface, brick work, insulating boards, etc.

surface, brick work, insulating boards, etc.

SAQ 2

(a)

(a) Write down the properties of a good distemper.Write down the properties of a good distemper. (b)

(b) Explain the procedure of application of distemper on a surface.Explain the procedure of application of distemper on a surface.

5.4 VARNISHES

Varnish is a solution of some resinous substance in alcohol, oil or turpentine. The Varnish is a solution of some resinous substance in alcohol, oil or turpentine. The process of covering the surface with varnish is known as varnishing. Varnishing process of covering the surface with varnish is known as varnishing. Varnishing

is done only on wooden surface. is done only on wooden surface.

5.4.1 5.4.1 Functions

Functions of

of Varnish

Varnish

Varnish performs the following functions : Varnish performs the following functions :

(i)

(i) It brings about brilliance to the painted surface.It brings about brilliance to the painted surface. (ii)

(ii) It protects the surface against adverse effects of the atmosphere.It protects the surface against adverse effects of the atmosphere. (iii)

(iii) It increases the durability of the paint film.It increases the durability of the paint film. (iv)

(iv) It beautifies the surface without hiding the beautiful grains of theIt beautifies the surface without hiding the beautiful grains of the wood.

wood.

Varnish plays an important part in finishing wooden surfaces of doors, windows, Varnish plays an important part in finishing wooden surfaces of doors, windows, floors, furniture, etc.

floors, furniture, etc.

5.4.2 5.4.2 Properties

Properties of

of Good

Good Varnish

Varnish

A good varnish should possess the following properties : A good varnish should possess the following properties :

(i)

(i) It It should should not not hide hide the the natural natural grains grains of of the the surface.surface. (ii)

(ii) It It should should not not shrink shrink or or show show cracks cracks after after drying.drying. (iii)

(iii) It It should should make make the the surface surface glossy.glossy. (iv)

(iv) It It should should dry dry rapidly.rapidly. (v)

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Engineering Materials _(vi)_{(vi) The thin}_{The thin film of}_{film of varnish developed}_{varnish developed after drying}_{after drying on th}_{on the surface}_{e surface should}_should

be tough, hard and durable. be tough, hard and durable. (vii)

(vii) The natural colour The natural colour of the varnish of the varnish should not should not fade away whenfade away when varnished surface is exposed to atmospheric action.

varnished surface is exposed to atmospheric action.

5.4.3 5.4.3 Constituents

Constituents of

of the

the Varnish

Varnish

A varnish has usually three elements : A varnish has usually three elements :

(i)

(i) Resins or resinous materialResins or resinous material (ii)

(ii) DriersDriers (iii)

(iii) SolventsSolvents

Resins or Resinous Material Resins or Resinous Material

Quality of varnish depends much upon the quality of resin used. Copal, lac, Quality of varnish depends much upon the quality of resin used. Copal, lac, amber and rosin are the commonly used resins for varnishes. Copal is

amber and rosin are the commonly used resins for varnishes. Copal is considered to be best.

considered to be best. Driers

Driers

Driers are used to accelerate the process of drying of the varnish. Litharge, Driers are used to accelerate the process of drying of the varnish. Litharge, lead, acetate, and white copper are the various types of driers, out of which lead, acetate, and white copper are the various types of driers, out of which litharge is mostly used.

litharge is mostly used. Solvents

Solvents

Selection of solvent is made depending upon the type of resin. Selection of solvent is made depending upon the type of resin.

Table 5.1 Table 5.1

Sl.

Sl. No. No. Name Name of of Resin Resin Solvent Solvent UsedUsed 1

1 Amber Amber and and copal copal Linseed Linseed oiloil 2

2 Lac Lac Methylated Methylated spiritspirit

5.4.4 5.4.4 Types

Types of

of Varnish

Varnish

The varnishes can be classified into following categories depending upon the The varnishes can be classified into following categories depending upon the solvent used :

solvent used : (i)

(i) Oil VarnishOil Varnish (ii)

(ii) Spirit VarnishSpirit Varnish (iii)

(iii) Turpentine VarnishTurpentine Varnish (iv)

(iv) Water VarnishWater Varnish (v)

(v) Asphalt VarnishAsphalt Varnish (vi)

(vi) Spar VarnishSpar Varnish (vii)

(vii) Flat VarnishFlat Varnish Oil Varnish

Oil Varnish

This type of varnish is manufactured by dissolving hard resins such as This type of varnish is manufactured by dissolving hard resins such as amber and copal in linseed oil. Turpentine may be used in small quantity to amber and copal in linseed oil. Turpentine may be used in small quantity to thin the varnish, and also to render it workable. Oil varnishes form a hard thin the varnish, and also to render it workable. Oil varnishes form a hard and durable film, but they dry slowly.

and durable film, but they dry slowly. Spirit Varnish

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This type of varnish is prepared by dissolving resins such as lac or shellac This type of varnish is prepared by dissolving resins such as lac or shellac in methylated spirit. This varnish dries very quickly and gets easily affected in methylated spirit. This varnish dries very quickly and gets easily affected by weather action. This varnish is mostly used for wood furniture.

by weather action. This varnish is mostly used for wood furniture. Turpentine Varnish

Turpentine Varnish

In this type of varnish, gum, dammar, mastic, and rosin like resins are In this type of varnish, gum, dammar, mastic, and rosin like resins are

dissolved in turpentine. These varnishes are light in colour and dry quickly. dissolved in turpentine. These varnishes are light in colour and dry quickly. Water Varnish

Water Varnish

This varnish is prepared by dissolving shellac in hot water. Shellac does not This varnish is prepared by dissolving shellac in hot water. Shellac does not dissolve readily in water and as such to accelerate the process of dissolving dissolve readily in water and as such to accelerate the process of dissolving shellac in water either ammonia or potash, or soda or borax is added. This shellac in water either ammonia or potash, or soda or borax is added. This varnish is used for painting pictures, posters and maps.

varnish is used for painting pictures, posters and maps. Asphalt Varnish

Asphalt Varnish

This varnish is obtained by dissolving melted asphalt in linseed oil. The This varnish is obtained by dissolving melted asphalt in linseed oil. The varnish may be thinned by adding suitable amount of either turpentine or varnish may be thinned by adding suitable amount of either turpentine or petroleum spirit. This varnish is used for varnishing fabricated iron and petroleum spirit. This varnish is used for varnishing fabricated iron and

steel product. steel product. Spar Varnish Spar Varnish

This varnish derives its name from its use. It is mostly used on spars and This varnish derives its name from its use. It is mostly used on spars and other exposed parts of the ships. It is very good weather resistant. It should other exposed parts of the ships. It is very good weather resistant. It should not be used indoor.

not be used indoor. Flat Varnish

Flat Varnish

This is an ordinary varnish to which material such as wax, finely divided This is an ordinary varnish to which material such as wax, finely divided silica and metallic soaps are added, to reduce the gloss of the varnished silica and metallic soaps are added, to reduce the gloss of the varnished surface. This varnish presents a dull appearance.

surface. This varnish presents a dull appearance.

5.4.5 5.4.5 Process

Process of

of Varnishing

Varnishing

Following operations are required to be carried out while varnishing a wooden Following operations are required to be carried out while varnishing a wooden surface :

surface :

Preparation of Surface Preparation of Surface

The surface to be varnished should be thoroughly rubbed smooth by means The surface to be varnished should be thoroughly rubbed smooth by means of sand paper and thoroughly cleaned from dust and dirt.

of sand paper and thoroughly cleaned from dust and dirt. Knotting

Knotting

It is the process by which knots on the surface of wood work are killed by It is the process by which knots on the surface of wood work are killed by applying certain substance over the knots. All the knots should be covered applying certain substance over the knots. All the knots should be covered with a hot preparation of red lead or glue size.

with a hot preparation of red lead or glue size. Stopping

Stopping

After knotting, the surface of wood work is stopped by means of hot weak After knotting, the surface of wood work is stopped by means of hot weak glue size. This coat fills all the pores of the surface. After stopping when glue size. This coat fills all the pores of the surface. After stopping when surface becomes dry, it is rubbed again with sand paper.

surface becomes dry, it is rubbed again with sand paper. Applying Varnish Coats

Applying Varnish Coats

After stopping process, varnish is applied on the surface in very thin coats. After stopping process, varnish is applied on the surface in very thin coats. Next coat is applied only when previously applied coat has dried. For Next coat is applied only when previously applied coat has dried. For

varnishing, fine brittle varnishing brush should be used. varnishing, fine brittle varnishing brush should be used.

SAQ 3

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118 118

Engineering Materials _(b)_(b) _{Explain the importance of varnishing a wood surface.}_{Explain the importance of varnishing a wood surface.}

(c)

(c) Describe the process of varnishing in brief.Describe the process of varnishing in brief.

5.5 SUMMARY

The paints, distempers and varnishes not only adds to the aesthetic appearance, The paints, distempers and varnishes not only adds to the aesthetic appearance, but also provides protective coating to the surface. In paints, enamel paint and but also provides protective coating to the surface. In paints, enamel paint and plastic emulsion paint are the most favoured paints, while cement paints like plastic emulsion paint are the most favoured paints, while cement paints like

snowcem remain popular as ever. Distempers are available in ready-made form in snowcem remain popular as ever. Distempers are available in ready-made form in the market and are far superior than white washing or colour washing. Varnishes the market and are far superior than white washing or colour washing. Varnishes are used to bring about brilliance to the painted surface. Varnish plays very

are used to bring about brilliance to the painted surface. Varnish plays very important role in finishing wooden surfaces of doors, windows, floors, furniture, important role in finishing wooden surfaces of doors, windows, floors, furniture, etc.

etc.

5.6 5.6 ANSWERS

ANSWERS TO

TO SAQs

SAQs

Refer the relevant preceding text in the unit or other useful books on the topic Refer the relevant preceding text in the unit or other useful books on the topic listed in Section “Further Reading” to get the answers of the SAQs.