Paints , Varnishes & constituents

1. PAINT:
The application of paint receives for more attention than in the past, whether the aim is to protect the
exterior of a building or beautify its interior.
Paint can be described as fluid paste prepared by dissolving base into vehicle along with coloring
pigment.
FUNCTIONS OF PAINTS:
The following are the functions of applying coats of paints to surfaces of timber iron or steel and plaster
Works in the engineering field
1. The main function is to protect the different surfaces from weathering effects of atmosphere and to
keep them in god condition for a longer period.
2. If also prevents decay of wooden members by wet and helps in extending the life of such members
3. It prevents corrosion of metallic surfaces and to prolong their life.
4. It also provides pleasing colourful and decorative appearance to the surfaces.
5. It also makes the different surfaces hygienically good, clean and safe.
PAINTS AND TYPES OF PAINTS:
Though there are number of types of paints, the following types of paints are discussed which are
commonly used for purposes.
 Oil paints
 Enamel paints
 Cement paints
 Aluminium paints
 Distempers.

2. OIL PAINTS:
The paints in which raw or boiled linseed oil used as vehicles are known as oil paints.
Ingredients of an Oil Paint:
The following are the ingredients of an oil paint
 Base
 Vehicle or carrier
 Colouring pigment
 Solvent or thinner
 Drier
 Inert filler
Base for Oil Paint:
The bases used in oil paint are :
 White lead
 Zinc white
 Red lead
 Oxide of iron
 Titanium white
 Lithophone
 Aluminium powder.
The commonly used base for wood work is white lead, where as for iron and steel work red lead is used.
Red lead sticks well and protects the surface effectively.
Functions of Base in an Oil Paint:
(a) It provides body to the paint.
(b) It provides an opaque coating and hides the surface to be painted

3. (c) It provides strength to the paint and reinforces the film after it has dried.
(d) It makes the film of the paint durable and more resistant to abrasion.
(e) In drying it minimises shrinkage cracks in the film.
(f) It prevents penetration of the paint to the underlying surface.
The properties and suitability of some common buses are discussed here
(i) White lead
It is the carbonate of lead and it is the cheapest base.
It is available in market both in powder form and stiff paste form. Paste is made by mixing
white lead with linseed oil. It is dense and waterproof. It is suitable for wooden surfaces. It
cannot resist the action of rusting. It is not suitable for iron surfaces. It is very poisonous.
(ii) Zinc White
This is an oxide of zinc and forms base for all the zinc paints. It is also available in powder
form well as in paste form. Paste is made by grinding with linseed oil. This has got good
spreading and binding power. It is smooth, transparent and non poisonous. It is suitable for
painting wood work but not commonly used due its cost.
(iii) Red Lead
It is an oxide of lead. Lead based paints are excellent moisture resisting and have good bond
with the surface. It is suitable for painting iron work.
(iv) Oxide of iron:
It forms the base of all iron paints. It mixes easily with the vehicle and is quite cheap and
durable. It is effective in preventing rusting of iron surfaces. It is most suitable for applying
priming coats for iron surface.
(v) Titanium white:
It is hydrated titanium dioxide mixed with barium sulphate in various propositions. It is non
poisonous and provides a thin, transparent and durable film. It is not affected by heat or
light. It is suitable for receiving coat of an enamel paint.
(vi) Litho phone:
It is a mixture of zinc sulphide and barium sulphate. It is cheap and can be easily applied on
the surface. When exposed to day light it changes colour & such it should be used for
interior works only. It should not be allowed to come to contact with water. It is more
suitable for interior works of inferior nature.
(vii) Aluminium powder
It is the base of all the aluminum paints. It prevents warping and cracking of wood. This
paint is generally used for priming coat of new wood work.
Vehicles or carriers
Vehicles or carriers are the liquid substances which hold the solid materials of the paints like base,
extender, colouring pigment in liquid suspension.

4. Vehicles act as a binder to the base and pigment and allow easy application. The vehicles used in oil
paints are:
1. Linseed oil
2. Poppy oil
3. Nut oil
4. Tongue oil
5. Dehydrated caster oil.
The most commonly used vehicles in all oil paint is linseed oil.
Functions of vehicle or carrier:
 It helps to spread the base and pigment evenly over the surface to be painted.
 It acts as binder for the base and pigment.
 It gets oxidised in drying and forms a thin tough durable and water proof film.
 It provides glues to the painted surface.
1. Linseed oil: It is clear transparent and practically odourless. The acids present in it reacts with the
oxygen of the atmosphere and forms a thin and hard film of the paints.
The various grades of Linseed oil are as follows:
(i) Raw Linseed oil: It requires more time for drying. It is suitable for interior work of superior nature.
(ii) Boiled linseed oil: It is thicker and dark in colour than raw oil. It dries quickly. As far as elasticity and
power of penetration are concerned boiled linseed oil is inferior to raw linseed oil. It is used for exterior
surfaces.
(iii) Pale boiled linseed oil: This is just like boiled linseed oil except that it does not possess a dark
colour. This vehicle is found suitable for painting plastered surfaces.
(iv) Double boiled linseed oil: It has quick drying qualities. It requires turpentine as thinning agent. It
can be used for external painting work and for painting plastered surfaces.
(v) Stand oil: It is prepared by heat treatment to raw linseed oil till it becomes thick like honey. It dries
slowly and provides a durable, clear and shining finish. It is suitable for interior work.
2. Poppy oil: It is extracted from poppy seeds. It is used for internal painting of light shades. It is more
suitable for paints of delicate colours.
3. Nut oil: This oil is obtained from ordinary walnuts. It dries rapidly and it is used for painting ordinary
works of temporary nature
4. Tung oil: This oil is superior than linseed oil and us preparing paints of superior quality

5. Pigments:
The colouring pigment is a finely divided solid substance which provides required shade and colour to
the paint. Colouring pigments of required shade are mixed with the paint. Sometimes two or more
pigments have to be used for getting desired shade,
Functions of pigment:
(i) It provides required shade and colour to the paint
(ii) It reduces the intensity of development of cracks due to drying of vehicle.
Solvent or Thinner:
A volatile substance that is added to the paint to make its application easy and smooth is called solvent,
thinner or diluent.
The common solvents are Turpentine, Petroleum spirits, naphthas and coaltar hydrocarbons.
Turpentine oil is the solvent which is generally used. The other solvents petroleum spirits and Naphtha
are under specific circumstances only.
For an oil paint, thinner or solvent is added to work properly. Thinners should not be used in the
exposed work and in the final coats, because it reduces the shade of the paint and also affected by
atmosphere.
Functions of the solvent:
 It modifies the consistency or stiffness of the paint and makes the application of paint easy and
smooth.
 It increases the workability of the paint.
 It provides better covering power to the paints.
 It evoporates quickly and facilitates quick drying of paints.

6. Dryer:
The metallic compounds which when added to the paint in small quantities accelerate the process of
drying of the paint. Driers absorb oxygen from atmosphere and transfer to the vehicle and accelerate
the process of drying. But driers have a tendency to affect the colour of the paints and also to destroy
the elasticity of the paint. Hence they should be used as per requirement.
The driers in oil paints may be in the form of liquid driers or pastes.
The commonly used dryers are Litharge, lead acetate, manganese sulphate and some cobalt
compounds.
Functions:
 It acts as a catalytic agent and accelerates the rate of drying of the film of paint.
 It makes the paint hard.
Inert Filler:
The material which acts as an adulterant and modifies the weight the paint is called as inert filler.
They do not react chemically with any of the other ingredients of the paint.
The inert fillers which are used in paint are:
(i) Whiting (powdered challi).
(ii) Silicates of alumina and magnesia
(iii) Silica.
(iv) Barium sulphate.
Functions of the inert filler
 It increases the bulk or volume of the paint.
 It improves the durability of paint.
 It reduces shrinkage and cracking of the paint.
 By adding inert filler, cost of the paint is reduced
ENAMEL PAINTS:

7.  These paints consists of metallic oxide white lead or zinc white ground with a small quantity of
oil mixed with petroleum spirit holding resinous matter in solution.
 Enamel paints dry slowly leaving a hard tough and elastic film which is smooth and durable.
 Enamel painted surfaces can be washed and are not affected by acids, alkalies, gases or stream.
Because their durability, they prove to be economical.
 Enamel paints are available in the market as readymade paint and can be thinned with
petroleum spirit.
Properties of Enamel Paints:
(i) They are good quality of paints.
(ii) They form a hard and impervious surface on drying.
(iii) They are durable and form a tough elastic and glossy film
(iv) They are not affected by cold and hot water.
(v) They are resistant to steam, fumes acids and alkalies.
(vi) They are costlier but economical in the long run.
Uses :
(i) Enamel paints are used for both external and internal work
(ii) Used for protecting timber and other wood based products
(iii) Used also for painting door and window frames.
(iv) They can be applied on plastered surfaces for better appearance
(v) They can be used for hygienic conditions in buildings like hospitals and hotels.
CEMENT PAINTS:
The paints containing cement and hydraulic lime mixed along with a colouring pigment are known as
cement paints. The base in this paint is coloured cement and water acts as a vehicle. No oil is added to
this paint. This paint is available in powder form. Water is added with the powdered paint just before its
application on the surface. Rough surfaces have good adhesion than smooth surfaces with this cement.
Composition
(i) White cement - 60 to 70%

8. (ii) Hydrated Lime - 10 to 20%
(iii) Calcium or sodium chloride - 4 to 5%
(iv) Calcium or aluminium stearate - 1%
(v) Titanium dioxide or zinc sulphide as white pigment - 2 to 5%
(vi) Colouring pigments upto 8%
Properties of Cement Paints
 This type of paint can be applied with a brush or sprayer.
 They provide a hard, durable water proof coating which resist the Penetration of distempers.
 Smooth mat finish can be obtained without any brush marks.
 They can be washed.
 They provide pleasing appearance.
 They lost longer.
Uses :
(i) They can be used as lasting finish on outer faces.
(ii) They can be applied on the surfaces of walls, ceilings in residential buildings as well as in
public buildings
ALUMINIUM PAINT:
 The paint containing aluminium powder suspended in spirit varnish or oil varnish is known as
aluminium paint.
 The suspension liquid, spirit or oil evaporates and a thin metallic film of aluminium is left on the
surface
Properties:
 These paints are highly resistant to hear.
 They resist corrosion due to sea water.

9.  They are impervious to moisture,
 This paint is visible in darkness because of its shinig colour
 It protects the surfaces of iron and steel.
 This paint has large covering capacity one litre of this paint cover about 200 Sq.m.
Uses :
 These paints are suitable for protecting metal work
 These paints are used in case of gas tanks, hot water pipes, marine pipes and oil storage tank
and radiators.
DISTEMPERS:
 Distempers are the paints consisting of powdered chalk, pigments and glue mixed in water.
These are also known as water paints.
 Distempers are available in the form of powder called dry distempers. Oil bound distemper are
available in the form of paste.
 Composition : Distempers consisting of whiting or powdered chalk as base, clean water as
vehicle with some glue and colouring pigment depending upon the nature of colour required.
 Oil bound distemper consists of an emulsion of an oil and water in which suitable pigments are
added. The oil used in the manufacture of oil bound distemper is linseed oil.
Properties of Distempers :
 They provide better and smooth surface than white colour wash.
 They are more durable.
 They provide pleasing appearance.
 They form the cheapest form of finish, with the except of white wash
Uses of Distempers
 They are applied on interior side of plastered walls and ceilings.
 These may be applied on plastered surfaces or surfaces which have been previously white
washed.
 They are not suitable for exposed situations.

10.  They are not suitable for the surfaces which remain wet for most of the time as bath rooms and
kitchen.
CHARACTERISTICS OF GOOD PAINT:
A good or an ideal paint should fulfill the following characteristics:
(i) It should cover the surface and should have good hiding power.
(ii) It should have good workability so that it can be applied smoothly on the surface.
(iii) It should form a thin uniform film over the surface to be painted
(iv) It should dry with in short time.
(v) There should not be any cracks after the painting.
(vi) When the paint dries, it should form a tough elastic and durable film
(vii) Due to atmospheric actions, the paint should not fade or change its colour.
(viii) It should produce a washable film.
(ix) It should not have any brush marks.
(x) It should have a pleasing appearance.
(xi) It should not contain any material which is injurious to underlying surface or to the painter.
(xii) It should be free from defects of chalking and blistering
VARNISHES:
 Varnish is a transparent or Semi transparent solution of resinous substance either in turpentine
or alcohol or linseed oil.
 In this type of paint resins are used instead of base. This can be prepared by mixing suitable
resins in a particular solvent.
 The solvent used in varnish may be an oil, when it is known as oil varnish or methylated spirit or
alcohol when it is termed as spirit varnish.
 Turpentine oil is added for thinning before its application, when the varnish is too thick.
 A small percentage of litharge is added in the varnish which acts as a drier.

11.  Spirit vanish is more commonly used due to its better appearance than oil varnish
Ingredients of a Varnish:
The resin or resinous substance, solvent and drier are the ingredients of a varnish.
(i) Resin or Resinous substance: Resinous substance is a natural or synthetic organic substance
which is soluble in some organic solvent. This acts as a base to the varnish. The commonly
used resins are copal, amber, shellac, mastic, gum and dammer etc.
(ii) Solvent: It acts as vehicle of the varnish. It helps in spreading the resin over the surface to be
varnished, it must have capacity to dissolve the resin in the varnish.
The solvents commonly used are boiled linseed oil, turpentine oil. In addition to
these alcoholic solvents like methyl and ethyl alcohols are used as solvents.
(iii) Driers: The ingredients that are used to accelerate the process of drying of the varnish are
called dryers. They are used in small proportions.
Characteristics of Varnish:
A Good varnish must have the following properties or characteristics
(iv) After drying the varnish should not shrink or show cracks.
(v) When the surface is exposed to atmospheric action, the natural colour of the varnish should
not fade away.
(vi) The thin film of varnish should be tough, hard and durable.
(vii) It should make the surface glossy.
(viii) It should give pleasing appearance.
(ix) It should provide a brilliant and decorative covering wooden surfaces without hiding the
natural grains
Types of Varnishes:
The varnishes are classified into the following categories depending upon the solvent used:
 Oil varnish
 Turpentine varnish
 Spirit varnish Water varnish
 Ashphalt varnish
 Spar varnish
 Flat varnish
(i) Oil Varnish : This type of varnish is manufactured by dissolving hard resins like amber and
copal in linseed oil. Turpentine may be used in very small quantities to thin varnish and also
to make it workable. These varnishes dry slowly but form a hard and durable film. These are
used for the exposed surfaces.

12. (ii) Turpentine varnish : Turpentine varnish is the varnish in which turpentine oil is used as
solvent. These varnishes consist of soft resins like common resin, mastic, gum, dammer etc.
dissolved in the best turpentine oil.
These varnishes are of light colour. They dry quickly but not so durable and tough as oil
varnishes.
(iii) Spirit varnish : Spirit varnish is prepared by dissolving resins like shellac in methylated spirit.
This varnish is used for wood furniture suitable may be used to give required shade to the
varnished surface.
(iv) Water varnish : Water varnish is prepared by dissolving shellac in hot water. Shellac usually
does not dissolve in water quickly. To accelerate the process of dissolving, either ammonia
or potash or soda is added to water. This varnish is used for painting pictures, posters and
maps.
(v) Asphalt varnish : Ashphalt varnish is obtained by dissolving melted ashphalt in linseed oil.
The varnish may be thinned by adding suitable amount of either turpentine or petroleum
spirit. This varnish is used for varnishing fabricated iron and steel products.
(vi) Spar varnish :It is mostly used on spars and other exposed parts of the ships. This varnish
derives the name by s use. It is very good weather resistant.
(vii) Flat - varnish : This is an ordinary varnish to which materials like wax, finely divided silica and
metallie are added to reduce the gloss of the varnished surface This varnish gives a dull
appearance. soaps
French Polish:
French polish is prepared by dissolving 150 grams of pure shell in one litre of methylated spirit. The
solution thus prepared is screened through a very fine cloth. Suitable pigment may be added to get
specific shade. This polish is used for superior wood work, wood furniture and hand rails.
APPLICATION OF PAINT:
General Procedure and Precaution:
The general restrictive precautions are as follows:
(i) The surface to be painted should be perfectly clean and dry
(ii) Painting work should be carried out in dry, warm weather after a dry spell. Damp weather
will cause the paint to peel off. Hot sun would cause blistering. In winter season painting
should be started only after dew has cleared is the morning and should be stopped before
the dew returns

13. (iii) The under coats and first coats must invariably be allowed to dry properly before applying
the final coat.
(iv) It should be planned such that a specific part (door, ceiling wall) is completed in the same
day.
Painting of Wood:
(1) Preparation of Surface: All wood work should be thoroughly seasoned and free of moisture
loose particles dust, grease or any other matter and must be finally sand papered. All
unevenness shall be rubbed down smooth W sand paper. Knots if any shall be covered with
putty red lead.
(2) Application of primer : The priming coat may be prepared at site of work or ready made primer
may be used. The primer can be prepared from a mixture of red lead, white lead and double
boiled linseed oil. The primer should applied evenly and smoothly by means of crossing and
laying off. The crossing and laying consists in brushing the surface hard for the first time and
then brushing alternately in opposite directions two or three times.
(3) After priming coat becomes dry all the cracks, loose joints dents and other defects in the surface
shall be filled with putty. When putty becomes dry, with sand paper the surface shall be rubbed
again. The surface shall be kept clean and dry.
The paint shall be continuously stirred in the containers so that is consistency is kept uniform. The
painting shall be done evenly and smoothly by means of crossing and laying off. Brushing shall be done
alternately in opposite directions two or three times.
When the first coat is sufficiently dried, the next coat of paint shall be applied in similar manner.
Painting the Metal Work:
Steel work in buildings is to be painted for decoration and protection from weather so that steel may
not become rusty.
New Steel Work:
(1) Preparation of Surface : When painting is to be done on new steel work, the surface is to be cleaned
to remove dirt, loose scales, rust and grease. The dirt and loose scales and rust are to be removed by
means of wire brushes, scrapers etc. The grease is to be removed by using line and water or caustic soda
and water. The cleaned surface is to be treated with phosphoric acid which protects the surface from
rust and provides a clean surface to which paint will adhere better.
(2) Application of paint: On cleaned surface, the priming coat of lime, red lead powder dissolved in
boiled linseed oil is applied with a good brush when the surface is perfectly dry. When the first coat
becomes thoroughly dry, a second or under coat of paint is applied with brush or by spraying. The paint
used for outer coat should be durable, elastic. The finished surface should be perfectly smooth and
even.

14. Repainting on old metallic surfaces (Ferrous and Galvanized):
 Before painting on the old metal surfaces it is necessary to that the surface is free from rust,
dust and grease.
 If the old painted surface is good and firm its removal unnecessary. But it shall be rubbed with
wire brushes and any loosened paint taken off.
 If the old painted surface is in bad condition and blistered the old paint shall be completely
removed with any specified paint remover. Usually caustic soda solution or blow lamp is used to
remove the paint
 After the surface is prepared for painting, new coats of approved paint are applied as in the case
of painting the new steel work. One or two coats may be applied.