3. 3
Learning Objectives
• Definition
• Functions of paints.
• Composition of oil paints.
• Preparation of oil paints.
• Characteristics of good paints.
• Types of paints, and properties of paints
• Defects in painting.
4. 4
Definitions
• Paint is a coating of fluid material applied over
timber and metal surface as protective coating
which on drying forms a thin film on surface
• Paint is a mixture of liquid or medium and a
coloring or pigment to impart color and provide
protective coating to the surface
• Oil based paints are polymers or pre-polymer
solutions which form a film upon evaporation of
the solvent
• Paint is a dispersion of pigments in a drying oil,
with addition of driers and thinners
5. 5
Definitions
• Varnish is a transparent or nearly
transparent solution of resinous material
and oil, alcohol or turpentine to form a
clear, tough, glossy film on woodwork
• Enamel. Bases like zinc oxide ground in
varnish. Dry quickly to furnish hard glossy
finish.
6. 6
Definitions
• Distemper is a comparatively cheap
decorative paint for walls and ceilings
applied on brickwork, or plastered
surfaces
• Water Wash and Color Wash. Fresh lime
slacked with water, mixed thoroughly,
screened and added with glue and may be
a pigment
7. 7
Definitions
• French Polish. Type of spirit varnish
prepared by dissolving resin in methylated
spirit at room temperature for use on
hardwood substances to hide grain
defects.
• Wax Polish. Bees wax dissolved in
turpentine used for highlighting the grain
over wooden surfaces.
8. 8
Functions of Paints
• To protect the surface from weathering
effects of the atmosphere and actions by
other liquids, fumes and gases
• To provide pleasing, colorful and
decorative appearance to the surfaces
• To prevent decay of wooden members
• To prevent corrosion of metallic surfaces
• To provide a smooth surface for easy
cleaning
11. 11
Types of Paints
• Oil Paint: ordinary paint
• Bituminous paint: prepared by dissolving asphalt or
bitumen in oil or petroleum
• Cement paint: It consists of cement and hydrated lime
mixed along with a coloring pigment
• Colloidal paint: a paint with no inert material
• Aluminum paint: aluminum powder suspended in spirit
varnish or oil varnish
• Asbestos paint: peculiar type, applied to places exposed
acidic gases and steam.
• Cellulose paint: prepared from nitro cotton celluloid
sheets
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Types of Paints
• Emulsion paint: It consists of polyvinyl acetate and
synthetic resin as binding material
• Enamel paint: It consists of white lead ground in small
quantity of oil and mixed with petroleum spirit and
resinous matter
• Graphite paint: black in color, applied on iron surfaces
• Luminous paint: contains calcium sulphide with varnish
• Silicate paint: prepared by mixing calcined ground silica
with resinous substances
• Anti-corrosive paint: consists of oil and strong drier
• Plastic paint: variety of plastic present, applied using
brush or spray painting.
• Synthetic rubber paint: prepared from resin
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Composition of Oil Paints
• Constituents of oil paints
– Base
– Vehicle – an oil, generally linseed oil
– Coloring pigment (s)
– Solvent or thinner
– Drier
– Inert filler
• By suitable variation of the type and proportion
of various constituents the paints are made as
– Dry
– Glossy
– flat
14. 14
Composition of Oil Paints - Base
• Base : principal constituent, a solid matter
forming the main body of paint and possessing
binding properties.
• White lead, red lead, zinc oxide, iron oxide,
metallic powders of aluminum, copper and
bronze, etc
– Makes the paint film harder and more resistant to
abrasion
– Forms an layer to obscure the surface
– Reduces shrinkage cracks on drying
15. 15
Composition of Oil Paints - Base
• White lead
– Cheapest and most commonly used base
– Greater covering power than all others
– Dense so good to obscure surfaces
– Weathers well
– Not suitable for delicate works as gets
discolored
– Not suitable for painting of iron work due to
rusting
16. 16
Composition of Oil Paints - Base
• Red lead
– Sticks well and protects against rusting. With
oil considered best for first coat or prime coat
– Good drier for linseed oil
• Lead paints are poisonous. Precautions
needed while spraying or scrapping paint
17. 17
Composition of Oil Paints - Base
• Zinc oxide or Zinc white
– Not affected by weather
– Takes a fine polish hence good for decoration works
– Not poisonous
– Less durable and more costly than lead based
• Iron oxide
– Used basically in finishing coat for iron work
– Prevents rust formation
– Comparatively cheaper
– Tints vary from yellowish brown to black
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Composition of Oil Paints - Vehicle
• Vehicle: Carrier liquid which carries solid
materials of base and helps them to spread
evenly on the surface to be painted. Linseed oil,
poppy oil, nut oil, soyabean oil, fish oil, latex
emulsions
– Oily liquid in which base and pigment are soluble
– Facilitates the paint to be conveniently spread evenly
over the surface
– Acts as a binder for the base and causes it to stick to
the surface
– On drying forms a tough and elastic film
19. 19
Composition of Oil Paints - Vehicle
• Raw linseed oil
– Thin, pale and transparent oil
– Sweet taste, no smell
– Becomes hard and stiff on exposure to air
– When spread in thin film, looks like varnish
– Dries very slowly
– Used for painting delicate interior work and
wood work
20. 20
Composition of Oil Paints - Vehicle
• Boiled linseed oil
– Thicker and darker in color (deep amber to rich brown)
– Dries quickly. On drying leaves a hard, glossy and
durable surface
– Has more area coverage capacity
– Used for exterior work
• Double boiled linseed oil
– Light in color as raw linseed oil but with different smell
– Dries quicker and gives better results
– Requires and thinning agent like turpentine oil
21. 21
Composition of Oil Paints - Pigment
• Coloring pigments: finely divided solid coloring
matter to provide shade, color to paint
– Blacks: lamp black, vegetable black, ivory black
– Blues: indigo, Prussian blue
– Yellows: chrome yellow, raw Siena, yellow ochre
– Greens: copper sulphate
– Browns: raw umber, burnt umber
– Red: red lead, vermillion, carmine
22. 22
Composition of Oil Paints - Thinner
• Solvent or thinner: A volatile liquid added
to prepare paint to increase fluidity thus
workability and ease of application
– Thinner helps penetration of paint in porous
surfaces
– Turpentine oil is most common thinner
– Excessive thinner dulls the colors and gloss
– Excessive thinner reduces protective value of
paint
23. 23
Composition of Oil Paints - Drier
• Drier: added to paint to quicken the drying
of vehicle
– Linseed oil dries by absorbing oxygen
– Drying process expedited by adding oxygen
rich substances
– Common driers are: Litharge, Red lead, Lead
acetate, Manganese dioxide, Zinc sulphate
– Excessive drier destroys the elasticity of paint
and causes flaking
– Drier is added to the paint just before use
24. 24
Composition of Oil Paints - Filler
• Inert filler
– An adulterant mixed to replace the base in
part thus reducing the cost of paint
– Commonly used fillers are silica, charcoal,
powdered chalk, aluminum silicate, barium
sulphate, etc
25. 25
Characteristics of Good Paints
• Should have a good body or spreading power
• Should work smoothly and freely to be laid in thin coat
• Should form durable, tough and wear resistant film upon
drying
• Color should not fade or change
• Painted surface should dry in about 9 hours
• Should become hard enough in 24 hours to take up
another coat
• Should not crack upon drying
• Should give a smooth and pleasing finish
• Should dry quickly
• Should not damage the painted surface
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Manufacture of Oil Paints
• The base (white lead) is thoroughly ground in oil
• Thinner (turpentine oil) is mixed to give it
necessary workability
• Pigment and drier are separately ground in
linseed oil and mixed with turpentine oil to make
it thin
• Pigment mixture intimately mixed with already
prepared base
• Prepared paint is strained through fine cloth or
seive
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Defects in Painting
• Cracking: cracks extending throughout the entire
thickness of paint, due to
– Improper seasoning of wood
– Excessive use of drier
– Application of too many coats
• Crazing and crocodiling: Hairline cracks in top
coat, due to
– Use of excessive oil
– Use of impure oil
– Insufficient drying of under coat
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Defects in Painting
• Blistering and peeling:
– Exposure of paint to strong sunshine
– Leaving oil or grease on the surface to be painted
– Painting a surface with moisture on surface or in
pores of wood
• Runs and sage:
– Application of too thick or slow drying paint
– Painting over a glossy surface
– Use of excessive drier
– Excessive humidity or rapid thermal changes during
drying period
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Defects in Painting
• Chalking: rub off with hands or clothes
– Use of insufficient oil in priming coat
• Washing off: deposition of water soluble
dissolved matter at lower edges forming
streaks
• Dull appearance: caused by use of
excessive drier or on aging
30. 30
Defects in Painting
• Slow drying:
– use of inferior or old oils
– Painting over damp surfaces
– Painting during unfavorable weather
• Yellowing of white paint:
– Use white enamel where glossy finish is
desired
– For indoors use linseed oil with yellow tint that
does not bleach unless exposed to sunshine
