Lesson 5 Paints.pptx

 Painting is the application to surfaces of
pigmented liquids or semi-liquids, which
subsequently harden.
Objectives:
1. Preservation
2. Protection
3. Decoration
4. To give a finish which is easy to clean and
maintain

Typically, there are four main components in a
paint:
1. Pigment,
2. Binder,
3. Liquid, and
4. Additives.

1. Pigment
 In its unmixed form, a pigment is simply a
powder which determines the color and
appearance of paint.
 Pigments also provide added bulk, helping to
thicken a paint when needed.
 There are two general categories of pigments:
a) Prime
b) Extender

a) Prime pigments
 Are mainly responsible for color or whiteness in a
paint, as well as the paint’s ability to hide
undesirable surface flaws.
 In white paints, titanium dioxide is used.
 Other pigments include: carbon pigments, iron
oxides, ultramarine pigments.
 Organic pigments yield the brightest colors, while
inorganic pigments yield less bright but more
durable colors.
 Carbon pigments are examples of organic
pigments while iron oxides are inorganic

b) Extender pigments
 They are designed to add bulk
 They influence the paint’s overall sheen, color
retention, and abrasion resistance.
 Silica and silicates are extender pigments that
increase the paint’s durability.
 Zinc oxide helps prevent mildew and
corrosion, and is especially useful in outdoor
applications.

2. Binder
 Provides adhesion, binds the pigment, and also
gives the paint resistance properties which make
the final coating tough and durable.
 The binder itself is a clear and glossy liquid.
 Depending on the ratio of pigment to binder,
the paint can assume varying levels of glossy
finish.
 Paints with less gloss have more binder per unit
of pigment, and tend to be more durable.

2. Binder – cont’d
 There are two specific types of binder:
a) Oil-based binder
 Once applied, the liquid factor of an oil-
based paint evaporates, and the binder then
reacts with the air to harden into place with
the pigment.

b) Latex-based binder
 Almost all water-based paints have a latex-
based binder.
 When the coating is applied, water evaporates
from the paint, leaving behind a film of
pigment and latex-based binder, which bind
together into one continuous coating.

3. Liquid – cont’d
 The liquid component of a paint is simply
responsible for transporting the binder and
pigment to the substrate surface.
 The type of liquid depends upon the other
components of the given paint.
 They increase workability and penetration
 Water is used for emulsion paint
 White spirit or turpentine for oil paint

3. Liquid – cont’d
 A paint thinner is an overall term for any
solvent that is used to thin paint or to remove
paint from brushes, rollers, and other painting
tools
 Examples of paint thinners include turpentine,
acetone, naphtha, toluene, and, mineral spirits
such as white spirit

4. Additives – cont’d
 These are used when certain properties need to
be manipulated or enhanced.
 Thickeners, are additives that help thicken the
paint to make application easier.
 Surfactants help disperse pigments within the
paint, ensuring the coat is even and stays in
place.
 Co-solvents help the binder film formation and
help prevent paint damage from occurring if the
paint is frozen.
 Co-solvents also make application easier by
lengthening the amount of time the paint can be
open before beginning to set.

1. Oil based paints
 Oil-based paint contains natural (linseed) or
synthetic (alkyd) oil as a base.
 It is a type of slow-drying paint that consists of
particles of pigment suspended in a drying oil,
commonly linseed oil.
 Available in priming, undercoat and finishing grades
 Finishes include matt, semi-matt, eggshell, satin,
gloss and enamel
 Oil-based paints are suitable for most applications
if used in conjunction with correct primer and
undercoat

Advantages of oil based paints
 Provide a hard and durable finish
 Available with different grades of sheen
 Covers many types of surfaces well
Disadvantages of oil based paints
 Often more expensive than latex paint
 Fresh oil paint tends to have an odor
 Longer drying time
 Special paint remover or stripper required to
remove enamel
 Health effects if improperly exposed to certain
paint removers

2. Water based paints
 Mostly called emulsion paints use water
instead of oil to carry the pigment and
binders of the paint.
 Emulsion paints are easily applied, quick
drying and can be obtained with a washable
finish and are suitable for most applications.
 Finishes include matt, eggshell, semi-gloss
and gloss.
 The two types of water-based paint: Acrylic
paint and latex paint.

2. Water based paints – cont’d
 Acrylic paint have more acrylic polymers than
latex paint.
 Because of this, acrylic paint typically costs
more and provides better adhesions,
durability, and resiliency.
 Latex paint contains a lower ratio of acrylic
polymers.

Benefits of water based paints
 Durability - Superior adhesion to most
substrates and has better flexibility than oil-
based paint.
 Color retention - Resists chalking and
fading.
 Ease of application - Smooth and even
application with less brush drag.
 Mildew resistance - Additives reduce mildew
growth and help maintain the paint's fresh
appearance.

Benefits of water based paints – cont’d
 Versatility - Can be used on a variety of
substrates, including wood, concrete, stucco,
brick, aluminum, vinyl, and galvanized metal.
 Odor – Significantly less odor than oil-based
paints.
 Drying time - Dries in one to six hours, which
permits same-day recoating.
 Clean-up - Easy clean-up with water and
soap.

Disadvantages of water based paints
 Water-based paints become difficult to use
when the temperature falls below 50 degrees
Fahrenheit.
 Water-based paints can show more brush
strokes and don’t “lay-flat” like oil-based
paints if proper technique isn’t used.
 Water-based paints can have poor adhesion
on raw metal, glossy, and shiny surfaces.
 Water-based paints can raise the grain on
un-primed wood.
 Water-based paints are not preferred in
humid, wet, and damp exterior applications.

 In diminishing order of smoothness, surfaces
can be described as:

1. Gloss
 Reflective finish, used for woodwork and
radiators
 It takes longer to dry

2. Silk and satin
 Mid-sheen' finishes, which means they look like a
slightly polished surface and reflect a bit of light
 Shiny finish, reflects light well and is smoother to
the touch.
 Commonly used for kitchens and bathrooms and
high-moisture areas.
 Easy to wipe down and scrub
 Because of the way that silk
reflects the light, any imperfections
in the wall finish are more obvious

2. Silk and satin – cont’d
 You can wipe silk wall finishes easily which makes
them very practical but if you have less-than-
perfect walls, all the lumps and bumps may show
up a bit more.
 A satin finish on woodwork helps to hide
imperfections and gives colour a softer
appearance.

3. Eggshell
 Has less of a sheen than silk or satin
 Used if a gloss finish is not desired.
 Between a matt and silk/satin finish.
 Gives a beautiful classic look to woodwork –
and can also be used on walls when you want
a heritage style look with a tough
finish.

4. Matt
 Paint with low reflection of light, rougher to
the touch.
 Used on interior walls and ceilings.
 Matt paint covers imperfections better and
doesn’t draw attention to lumps and bumps.

 Painting should not be carried out:
a) In wet, damp, or foggy weather
b) On surfaces below about 4˚C
c) In direct sunlight
d) In dusty conditions
 Each coat should be thoroughly dry before
the next coat is applied
 Good ventilation is required to dry paints and
to remove noxious fumes

 Humid conditions are detrimental because
they cause:
a) Delay in drying of paints
b) Entrapped moisture which reduces the
adhesion of paints
c) Reduced durability of the paint
d) Reduced gloss of finishes
e) Corrosion of ferrous metals

Surface Preparation
 Preparation of the surface to receive the paint
is of the utmost importance
 Poor preparation is one of the chief causes of
paint failure
 Preparation consists of:
 Removing all dirt, grease and dust
 Ensuring that the surface will provide an
adequate key for the paint to be applied

Build up of paint coats
1. Priming Coats
 Priming ensures better adhesion of paint to the
surface, increases paint durability, and provides
additional protection for the material being painted
 Used on unpainted surfaces to obtain the necessary
adhesion
 Inhibits corrosion of ferrous metals.

2. Undercoats
 Used on top of the primer after any defects have
been made good with a suitable stopper or filler.
 The primary function of an undercoat is to give the
opacity and buildup to cover surface imperfections
before application of the finishing coat(s).
 An undercoat’s key purpose is to provide a smooth,
uniform, even surface for topcoats.
 For new surfaces, use a primer, for an existing
surface that has been painted before, use an
undercoat

3. Finish
 Applied directly over the undercoating in one or
more coats to impart the required colour and
finish.

Paints can be applied by:
1. Brush
 The correct type, size and quality of brush must be
selected and used.
 Brush application requires a high degree of skill to
achieve a good finish.

1. Brush – cont’d
 Brush application is used for decorative coating of
relatively small and complex areas.
 Brush painting is a slow application method but it
provides good penetration of the paint.
 Brush application prevents paint losses associated
with the spray application method.

2. Roller
 Simple and inexpensive method of quickly and
cleanly applying a wide range of paints to flat and
textured surfaces.
 Roller heads vary in size from 50 to 450 mm wide
with various covers such as sheepskin, synthetic
pile fibers, and foamed
polystyrene.
 All paint applicators must be
thoroughly cleaned after use.

3. Spray
 Compressed air sprays or airless sprays are used
for building works.
 A high degree of skill is required to achieve a good
finish.

3. Spray – cont’d
 In the air spray application method the paint in
form of atomized droplets is delivered by a stream
of compressed air.
 The paint is pumped from the tank into the gun
where it is atomized (broken into small droplets) by
the flowing compressed air
 Spray application is a simple method which is
capable to coat objects of various shapes and
dimensions.

 The disadvantage of the air spray application is
unavoidable overspray: losses of the paint and
expensive organic solvents and thinners.
 The method requires additional investment in
safety equipment in order to protect the workers
exposed to the hazardous solvent vapors.

 In the airless spray the paint is not mixed with air.
 The liquid paint is delivered to the gun by a
hydraulic pump producing a high pressure of up to
7000 psi

 The pressurized paint is atomized in the gun nozzle
commonly made of tungsten carbide.
 It has an orifice, diameter of which (together with the
paint viscosity and the pump pressure) determines the
delivery rate and controls the coating thickness.
 Using high pressure pumps and preheated paints
allows to apply high viscosity paints having a
decreased amount of solvents and thinners (e.g. High-
solids paints).
 Lower solvent content in the paints for airless
application results in a reduced overspray.

 Determine the paint colour for your wall.
 Prepare the wall for painting to achieve the
best finish.
 Place drop cloths on floors and on any
furnishings that must remain in the room.
 Apply painter's masking tape to fittings which
can't be removed and any edges which may
be fiddly and difficult to paint around, such
as skirting boards and fixed shelving.
 Mix the paint with the required solvent and
stir the paint thoroughly.

Requirements for roller painting

To paint a wall with a roller, start at
the top corner of the project area,
where you have cut in a three-to
four-inch wide area around the
perimeter with a brush
Working in a three-by-three area,
roll a "W" onto the wall. This will help
place an even distribution of paint
onto the wall. Continue rolling from
the top edge of the wall to the
bottom, filling in the "W" as you go.
Repeat the "W" process until
the entire wall is covered.

1. Timber
 The timber should have a moisture content of less
than 18%.
 The timber surface should be prepared using an
abrasive paper to produce a smooth surface
 The surface should be brushed and wiped free of
dust
 Any grease should be removed with a suitable
spirit.
 Knots should be treated with a shellac based
primer so that the knot doesn’t bleed through the
top (finish) coat.
 The knot may be cut out and replaced with sound
timber.

 Cracks and fixing holes should be stopped and filled
with an appropriate filler after the application of the
priming coat.
 Each coat of paint must be allowed to dry hard and
be rubbed down with a fine abrasive paper before
applying the next coat.
 On previously painted surfaces if the paint is in a
reasonable condition the surface will only require
cleaning and rubbing down before repainting;
 Poor condition paint must be removed completely

a) Prepare the surface b) Apply the primer
c) Rub down the primer d) Apply the desired paint

2. Iron and Steel
 Priming is a must for painting metal.
 If the metal surface has been painted before,
remove old paint, rust, debris, grease, dirt using a
wire brush or wire-brush tool.
 If the metal doesn't have paint on it or it's smooth,
take a scuffing pad/sand paper and rub it along
the metal.
 These pads will lightly etch the surface of the
metal, which will allow the primer to stick more
effectively.

2. Iron and Steel – cont’d
 Apply a primer specifically manufactured for metal
 Apply the paint either by brush or spray painting.
The latter is easier

Painting with a
brush
Painting with a roller
Spray painting

2. Iron and Steel – cont’d
 The metal needs to cure for 36 to 48 hours before
moving it.
 Ensure the object is in an area that won’t be
affected by extreme temperatures or direct
sunlight when drying.

3. Plaster
 Ensure the plaster surface is perfectly dry, smooth
and free of defects before applying any coats of
paint, especially when using gloss paints.
 Plaster and mortar splashes should be scrapped off,
irregularities rubbed down and the resultant dust
removed.
 Cracks and defects should be filed up and rubbed
down
 Plaster which contains lime can be alkaline and such
surfaces should be treated with an alkali-resistant
primer when the surface is dry before applying the
final coats of paint.

Rubbing down the wall Filling cracks
Painting with roller

 These may be due to:
a) Poor or incorrect preparation of the surface
b) Poor application of the paint
c) Chemical reactions
 The general remedy is to:
a) Remove all the affected paint
b) Carry out the correct preparation of the surface
c) Applying new coats of paint in the correct manner

1. Bleeding
 Bleeding is a coating defect causing unwanted
discoloration on the upper coat.
 This is caused by the diffusion of pigments and/or
dye stuffs from the lower coat of coating film to
the upper coat
 Usually caused by applying an incorrect paint over
another.
 Remedy is to remove affected paint surface and
repaint with correct type of overcoat paint.

 Either there is too much moisture behind the newly
applied paint, causing the water-soluble pigment
to seep to the surface, or the initial color is too
bright or too dark to be covered with a
conventional paint.

2. Blistering
 Usually caused by poor presentation allowing resin
or moisture to be entrapped, the subsequent
expansion causing the defect.
 Remedy is to remove all the coats of paint and
ensure that the surface is dry before repainting.

3. Blooming
 Mistiness usually on high gloss or varnished
surfaces due to the presence of moisture during
application.
 It can be avoided by not painting under these
conditions.
 Remedy is to remove affected paint
and repaint.

4. Chalking
 Powdering of the paint surface due to natural
ageing or the use of poor-quality paint
 Remedy is to remove paint if necessary, prepare
surface and repaint.

5. Cracking and crazing
 Usually due to unequal elasticity of successive
coats of paint.
 Remedy is to remove affected paint and repaint
with compatible coats of paint.

6. Flaking and Peeling
 Can be due to:
a) Poor adhesion
b) Presence of moisture
c) Painting over unclean areas
d) Poor preparation
 Remedy is to remove
defective paint, prepare
surface and repaint.

7. Grinning
 Due to poor opacity of paint film allowing paint
coat below or background to show through
 Could be the result of:
a) Poor application
b) Incorrect thinning
c) The use of the wrong colour.
 Remedy is to apply further
coats of paint to obtain
a satisfactory surface.

8. Saponification
 Formation of soap from alkali present in or on
surface painted.
 The paint is ultimately destroyed and a brown
liquid appears on the surface.
 Remedy is to remove the
paint films and seal
the alkaline with an surface
alkali-resistant primer
before repainting.

9. Bittiness
 A defect in which the appearance of a paint finish
is marred by small particles of extraneous material,
typically dust, grit, broken paint skin and
fragments of bristle from brushes
 It is usually due to lack of care and attention to
cleanliness in preparing surfaces, materials and
equipment

10. Curtaining (running, sagging)
 Uneven or thick application of paint
 The usual causes are uneven application to broad,
flat surfaces or over-application to moldings and
to rough or contoured surfaces.
 Prevent curtaining by applying the coating evenly
and avoid heavy coats

11. Cissing
 Failure of paint to adhere properly to a surface.
 Freshly applied paint recedes from the surface leaving
small craters or bare areas.
 The usual cause is contamination of the surface, e.g.
by grease, oil, wax polish or silicones.
 It may also occur when water-thinned paints are
applied over glossy or semi-gloss oil based coatings.
 It can be prevented by ensuring that the surface is
clean and by removing oil based coatings before
applying water-thinned materials.
 When cissing has occurred, the paint must be allowed
to harden before it is rubbed down and recoated

12. Moulds growth
 These are unsightly and may be destructive of
paint coatings.
 Moisture is an essential requirement for the
development and growth of moulds and they are
especially likely to occur in conditions of high
humidity or on surfaces with a high moisture
content.
 Remedial treatment should include reduction in
humidity and moisture content if possible, and
the application of fungicidal washes to kill the
growth.

13. Ropiness (brush marking)
 Appearance of coarse or heavy brushmarks in a paint
finish.
 May be caused by using paint which is excessively thick
as a result of age or evaporation of solvent; by
unskilled or careless application, (especially of the
undercoats), or the use of brushes of unsuitable size or
poor quality.
 To reinstate a ‘ropy’ surface the paint must be allowed
to harden thoroughly before rubbing down, preferably
with a waterproof abrasive paper and water, and
recoating.
 With water thinned paints, brushmarking can be caused
by overbrushing or inadequate thinning, particularly on
very absorbent surfaces.

14. Rust damage
 Caused due to insufficient preparation of the metal,
including incomplete removal of mill scale.
 Breakdowns are usually first of all seen as blistering or
cratering and followed by the complete breakdown, as
wholesale lifting and flaking.
 Complete removal of the paint corrosion and mill scale
is essential before repainting.
 The priming paint should be applied immediately after
preparation, ensuring that a suitable primer and
adequate paint systems are used.

15. Shriveling (raveling, wrinkling)
 Wrinkling of the outer surface of a paint coating.
 It occurs most frequently with gloss finishes on
exterior work in conditions conducive to the rapid
formation of a surface ‘skin’, e.g. in dry, bright,
windy weather.
 Given these conditions, shriveling is likely to be
most severe if the paint has been heavily applied.
 The formation of a surface ‘skin’ reduces the
supply of oxygen to the underlying paint; if the
coating is excessively thick, it may take several
days or even weeks to dry and harden completely.

14. Shriveling (raveling, wrinkling)

 Road Marking Paint is formulated for use on
concrete and bituminous surfaces of roads,
curbs and airfield runways.
 It is based on a rubberized resin coupled with
good quality pigments and selected fillers.
 It is characterised by hard-wearing film
properties which give good durability on
normal traffic pressure.

 Application is done by:
a) Roller
b) Spray : Use airless spray or conventional
spray.
c) Brush : Recommended to paint corners and
edges.
 Colour range are Yellow and White
 Ensure that the road surface is clean, free
from dust and moisture.
 Heavy deposits of paint require removal.

Road marking spray and
roller applicator
Application
by brush

 Heat the material to 180-200°C in the pre-
heater with adequate agitation till the
material becomes a homogenized liquid.
 On aged asphalt roads and concrete roads
application of Thermoplastic Primer coat is
recommended for proper bonding of the
material with the road surface.
 Ensure that the primer is thoroughly dry and
void of solvent prior to application of the
thermoplastic material.

 Do not hold thermoplastic above 180°C for
more than 6 hours.
 Do not heat the material above 200°C at any
time.
 Change in colour indicates that the material
has been scorched owing to overheating and
needs to be discarded.

Lesson 5 Paints.pptx

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Lesson 5 Paints.pptx