2 conceptos de pintura - la preparacion
TRANSCRIPT
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FORM ACIONPOSTVENTA
Service
PREPARAT ION
PAINTING
CONCEPTS
2
BASIC SELF-STUDY MANUALS
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No part of this document may be reproduced or transmitted in any form or by any means, electronic, mechanical, photocopyng, recording, or
otherwise without the prior written permission of the copyright holders.
TITLE: Painting Concepts. Preparation (B.M. No 2) - AUTHOR: Service Organisation - SEAT, S.A. Zona Franca, Calle 2Register of business names Barcelona. Volume 23662, Folio 1, Page 56855
1st edition - PUBLICATION DATE: January 97 - LEGAL REGISTER: B.4504-98Preprinting and printing: TECFOTO, S.L. - Ciutat de Granada, 55 - 08005 - 08018 Barcelona - Desing and Composition: WIN&KEN
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C O N T E N T S
OXIDATION OF STEEL 4-5
ORIGINAL BODYWORK PAINTING 6-10
REPAIR PAINTING 11
MATERIALS FOR REPAINTING:
ABRASIVES 12-16
MATERIALS FOR REPAINTING:
PAINTS 17-21
PAINTS:
CLASSIFICATION ACCORDING TO THE METHOD OF DRYING 22-23
REPAIR SHOP REPAINTING PROCESSES 24
PREPARATORY PAINTING:
PRE-TREATMENT OF SURFACES TO BE PAINTED 25-27
PREPARATORY PAINTING:
APPLICATION OF PROTECTIVE PRIMERS 28-29
PREPARATORY PAINTING:
APPLICATION OF STOPPERS 30-31
PREPARATORY PAINTING:
FLATTING OF STOPPERS 32-33
PREPARATORY PAINTING:
APPLICATION OF FILLERS 34-37
PREPARATORY PAINTING:
FLATTING OF FILLERS 38-39
SELF-CHECK EXERCISES 40-42
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The oxidation
The chemical process of
oxidation consists in the atoms of
the oxidised material losing
electrons to another material, in
other words, this process involves
the exchange of electrons
between two materials. The
material which looses the
electrons is known as the
corroded material, and the
substance which gains the
electrons as corrosive (capable of
corroding other materials)The reduction process is the
inverse of oxidation, a material
which undergoes reduction gains
electrons.
Materials have different tendencies
to either gain or loose electrons,
metals such as steel, for example,
have a tendency to loose electrons
and will corrode with time if they
are not protected properly.
However other metals such as
copper are much less prone to
undergo oxidation and this can
only occur by adding certain
strong acid oxidising agents. Some
metals, such as gold, are almost
impossible to corrode and have
very little tendency to loose
electrons.
When two metals with different
corrosion tendencies are placed
in contact, the material with
greater corrosion tendency
passes electrons to the material
with less corrosion tendency and
thus corrosion begins.
In this case, the material which
looses electrons is known as the
anode and the material which
gains electrons is known as the
cathode, since this is a chemical
process which leads to the
formation of a battery, producing
the flow of electrons from the
anode to the cathode.
Anti-corrosionprotection
Presently car bodies are built
with sheet steel which has a
tendency to undergo this process
of oxidation by corrosion. For
this reason the automobile
manufacturers place utmost
importance in the protection of
the steel against corrosion, and
the complex operation of
painting at the factories is
designed to ensure optimum
protection of the car body
throughout its entire service life.
The method used to protect the
car body, consists in insulating it
from the atmosphere by covering
it with a protective layer in the
form of paint.
Steel can also be protected from
corrosion by placing it in contact
with a metal which has a greater
OX IDAT IO N O F ST E E L
The steel used to build cars needs to be protected
from oxidation:
Zinc coating and painting accomplishes this task.
Oxidisedmaterial
Oxidisingmaterial
Tendency
tooxidise
ZINC
IRON
COPPER
GOLD
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tendency to corrode than the
steel itself, so that the corrosion
of the steel does not start until
the protecting metal has
completely corroded away.
The most common metal used
for this purpose is zinc, giving
rise to the term known as
galvanised or zinc treated metals
which have an excellent
resistance to corrosion.
When paint is also added on top
of zinc protection, the anti-
corrosion resistance will
be optimised and this type of
protection is known as the
duplex system.
The reason for the excellent
protection offered by zinc, is due
to the fact that the zinc particles
do not fall off under the action of
corrosion, they remain attached
to the metal causing the
corrosion to progress very
slowly. The contrary occurs with
steel, where the corroded
material constantly falls off,
exposing new layers to attack
by corrosion.
Summarising, zinc has a greater
tendency to corrode than steel,
but zinc corrosion progresses
much slower than steel
corrosion.
5
I N T E R E S T I N G F A C T S
Electrolytic corrosion of steel
When steel is in contact with water, either
directly or through the humidity in the air, a
chemical reaction takes place which leads to
the corrosion of the steel.
This is due to the fact that zones of different
corrosion tendencies exist in the steel called
anodic and cathodic zones.These are the
result of variations in the composition,
structure, or tension within the steel.
A flow of elect rons takes place between
these two points through the steel itself and
this circuit is completed by the humidity on
the surface with the help of H+ and OH-
ions resulting from the hydrolysis of water
molecules.If this surface humidity did not exist,
corrosion would not take place since the
circuit would not be closed and the electrons
could not circulate.
If on the other hand, salt is found in the
atmosphere, in coastal areas for example,
the salt dissolved in the water would
accelerate the corrosion since it provides
more ions for circulation and completion of
the electrical circuit for the movement of
electrons.
For this reason, the presence of a protective
layer of material such as paint insulates thesurface of the steel from humidity and
makes the circulation of the ions more
difficult in the interface between metal and
paint.
ELECTROLYTIC OXIDATION OF STEEL
Anodic point (oxidation)
Oxygen fromatmosphere
Humiditylayer
Steel plate
Iron oxide
Cathodic point
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Zinc treatment of
metal sheet
Nowadays, anti-corrosion
protection begins even before
the parts are fitted to the
vehicle, s ince the steel sheet
used is covered with zinc, these
are the so called zinc pre-
treated parts.
This coating provides the initial
anti-corrosion protection, if for
any reason the paint layer is
damaged on the vehicle,
exposing bare metal, the
corrosion will not progress
on the steel but it will start on
the zinc: this zinc protection is
known as sacrificial.
Metal sheet preparation:
cleaning and degreasing
When the assembly has been
completed, the f irst operation
which is done on the paint line
is the cleaning and degreasing of
the steel.
During the operations of
welding, cutting and assembly,
greases and waxes are used
which smear the bodywork and
leave residues. Under these
condit ions, it is impossible to
achieve good paint adherence.
The bodywork has to be dipped
and sprayed with degreasing
solutions to eliminate these
residues, and the subsequent
rinsing and drying will ensure
that the bodywork is in perfect
condition to receive the
protective and decorative layers
of paint.
Phosphatising
The application of this
treatment has two main
objectives: provide a good base
on the metal and ensure better
adhesion of subsequent paint
layers and to protect the
bodywork from corrosion.
This treatment is carried out by
dipping the bodies in large baths
containing various phosphate
salts in solution. These solutions
react with the steel and form
a crystalline layer of metal
phosphate on the sheet steel
which firmly adheres to the
entire body.
Cataphoresis
primer
The following protective coating
applied to the body is known as
a cataphoretic primer or
cataphoresis treatment. The
particularity of this treatment
lies in the way the paint layer is
deposited on the surface.
This is done by a process
of electroplating or
electrophoresis resulting from
the passage of an electric
ORIGINAL BODYWORK PAINTING
The original paint on cars and spare parts provides an optimum
anti corrosion protection. Every effort should be made in all painting and repair
operations to conserve paint quality.
I N T E R E S T I N G F A C T S
Galvanising and zinc treatment
of metal sheet parts
The z inc (Zn) appl ied to meta l sheet
parts fitted to the bodywork is commonly
known as galvanising or zinc treatment
depending how the zinc was deposited on
the metal.This could be by immersion in
a molten zinc bath or by electrolysis.
The thickens of the zinc coating could
vary depending on the subsequent use of
the sheet metal: the average thickness is
about 5 m (*), and the stee l cou ld be
treated on one or both sides.
External surfaces which need to be
painted and therefore require a better
finish are usually treated using the
electrolytic (electroplating) process.
* m is the symbol for the micron, one micron is equal to
1/1000 of a millimetre
STEEL SHEET TREATED WITH
ZINC ON BOTH SIDES
Zinc
Zinc
Steel
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current. The ionised paint
particles are dissolved in a
solution made up basically of
water. The paint particles
adhere to the bodywork
because they have positive
electrical charges.
The bodies or parts to be
painted are generally totally
immersed in the electrolyte
solution containing dissolved
paint. The metallic part to be
painted is connected to the
negative pole of a direct
current supply, and the posit ive
pole is connected to a series of
inert anodes placed within the
bath.
The application of electrical
current causes the paint
particles with positive charges
to be drawn with the flow of
electrons towards the body, on
which they become deposited.
Since the deposition of paint is
dependant on the current, paint
is deposited on all surfaces,
both internal and external, and
this is one of the major
advantages of the
electrophoresis process, as well
as the fact that the paint
coating is very uniform in
thickness.
The advantages of this method
of treatment are obvious, s ince
it is possible to reach all the
hidden corners of modern
bodies.
When this process of
electrodeposition of the paint has
been completed, the body is
rinsed several times in order to
recover any paint which has not
adhered to the body. Finally, it is
washed with de-mineralised
water and left to drain, and then
introduced to the drying ovens to
cure and harden the paint at a
temperature of 180 C.
When this operation is
completed, the bodywork will
then have an excellent anti-
corrosion protection.
The bodywork parts supplied by
the parts department also
receive a cataphoretic
protection treatment, this
ensures that these parts do not
corrode in the warehouses.
CATAPHORESIS
Appl ica tion pro ces s
for primer paint by cathodic
electrophoresis.
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Putty and sealant
In joints or panel overlap areas,
such as the folds around frames
or due to overlapping of sheet
metal for strengthening, the
normal paints are not sufficient
to provide proper protection of
the bare edge of the metal. For
this reason it is necessary to
apply sealant or putty.
These products are generally
made with a polyurethane base
and have excellent viscosity
properties. They are squeezed
out in circular or oval section
strips, and placed on the bare
edge of the metal, thus avoiding
corrosion attack of these
exposed areas.
At the same time, in areas of
severe exposure to stone
chipping, a special stone chip
protection coating is applied.
These are high viscosity paints
which remain permanently
flexible and their function is to
absorb impacts which could
break the cataphoresis coating
and thus cause corrosion due to
perforation of the paint film.
These stone protection paints
are generally applied to the
lower side of the door sills and
the wheel arches.
Surface filler or
foundation paint coat
The next coat of paint applied
to the bodywork has many
varied names, surface filler, base
coat, undercoat, sealing base,
although the first two are the
most appropriate. The task of the
surface filler is to cover small
defects and unify the surface of
the bodywork before the
application of the finishing paint
layers while, at the same time,
providing some anti-corrosion
protection.
Presently the method used by
automobile manufacturers for the
application of these paints is
known as centrifugal electrostatic
projection. This consists in
applying the paint with special
nozzles, that give the paint an
electrostatic charge and then
project them on to the body
which is also electrically charged.
This method improves the
APPLICATION OF PUTTY
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SINGLE LAYER
Lacquersingle layer
Cataphoresis
Cataphoresis
Phosphate
Phosphate
Zinc
Zinc
DUAL LAYER
Clearcoat
2 coat base
Filler
Filler
Protective layers applied to steel sheet
on automobiles during original
painting using single layer and dual
layer processes.
efficiency of paint use.
The surface filler is dried in
ovens at a temperature of
170 C.When the paint has
hardened and dried at ambient
temperature, it is possible to
correct any light defects by
flatting.The dust particles created
must then be cleaned off before
passing the body for the final
paint coats.
The only sure way to achieve an
excellent result is by following
the above methods and always
applying the final coats on the
preparation coats mentioned. For
this reason, it is also important
that only good quality
preparation coats are used
(acrylic 2 pack surface fillers).
Finishes
The final paint coats on the
bodywork are designed to
provide it with several properties
such as: final appearance, colour,
shine, specific effects and
hardness.
According to the type of finish
the final paint could be applied
in one coat, known as a s ingle
coat or in two coats: the f irst is
a colour base (known as a 2
coat base), and f inally a clear
coat is placed on top. These two
finish procedures are therefore
known as the single coat and
dual coat f inishes.
In both cases, the centrifugal
electrostatic projection spray
method is used since this gives
better results than the traditional
compressed air projection
method. However, in the case of
metallic paints, the compressed
air projection spray method is
still used, since the orientation of
the aluminium particles produced
by the electrostatic method
would be too difficult for the
external repair workshops to
reproduce.
The final paint coat provides the
specific effect desired which
could be pastel, metallic or pearl
effect and gives the shine, finish
and hardness required to protect
the undercoats. In the case of the
single coat paints, the paint itself
provides the protection and with
metallic paint, this protection is
provided by the clearcoat varnish
layer.
Wax and
anticorrosion
When the final coat of paint has
been applied, the areas of the
body such as the various holes
and cavit ies, which could be
prone to rust due to their
exposure to water accumulation
and condensation, are wax
treated to ensure their long 9
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Cleaning anddegreasing
Cleaning
Underbodypainting
Cataphoresis
Bath recovery
Filler
Rinsing
Inspection
Finishpaints
Rinsing
Phosphating
Sealing
ORIGINAL PAINTING OF BODYWORK
lasting and efficient protection
from corrosion.
Nowadays, in certain cases
polyurethane foam which
expands on injection is used
instead of wax, to protect
hidden cavities (interior of
pillars and side members etc.).
The protection offered is
similar to wax treatment since
the foam expands and fills the
cavit ies, thus preventing
condensation and moisture
accumulation.Paint process diagram in a modern
automobile factory.
DRYIN
G
DRYIN
G
TROC
KNEN
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REPAIR PA I N T I N G
Differences with
regard to original
paint
When a vehicle is involved in an
accident and the consequence is
the deterioration of the
bodywork, the painting of the
affected parts, which are either
repaired or replaced, is essential
to ensure recovery of the
bodywork protection, as well as
the external vehicle appearance.
There is a considerable difference
between the paint applied to the
bodywork in production and the
paint used for repairs.The first
main difference is that the
bodywork in production is painted
alone without all the cladding,
trim, mechanical components etc.,
while during service repairs,
except in the case of complete
body shell replacement, all these
components are not removed
from the vehicle. For this reason
the paints used in service repairs
should be low temperature drying,
since it is not possible to subject
the plastics, mechanical and
electrical components to
temperatures above 60 C
or 70 C.
Also, the fact that a service
repaint has to be done, usually
means that a heavy thickness of
paint or undercoat needs to be
applied, to cover up defects not
repairable by the panel beater.
Care must be taken as well, to
protect the parts of the body
which will not be repainted with
the appropriate materials.
In order to carry out painting
repairs, the specific tools,
equipment and installations are
required, and repair procedures
for the application of the
materials used need to be
followed.
We will now take a closer look at
the materials used in the
paintshop: the abrasives and the
paints.
The main equipment and tools will
be studied in the basic self study
manual No. 5.
Paint repairs done in automobile paintshops should be capable of reproducing,
with the help of the tools and equipment available, all the aesthetic and protection
characteristics of the original paint.
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Applications of
flatting in automobile
repainting
In order to apply paint on any
surface and ensure its perfect
adhesion, certain surface
condit ions are required: in
other words, a specif ic
roughness depending on the
type of paint which will be
applied and the material of the
base to be painted.
It is very diff icult to achieve
good adhesion on a high gloss
surface with any kind of paint.
For this reason it is essential to
do a proper flatting to achieve
the correct surface roughness
on any surface which has lost
its normal adhesion properties,
such as dried paints, stamped
panels, cataphoresis treated
parts for the parts department,
etc.
It will also be necessary to use
surface fillers on parts repaired
by panel beaters, which wil l
need to be sanded down later in
order to level out the surface
to the desired shape.
Basics of flatting
Sanding or flatting consists in
the removal of material from asurface by mechanical means, in
other words, by sl iding a harder
material over a surface with
certain precis ion, which then
penetrates the sanded surface.
Flatting materials are generally
composed of very hard
substances such as: emery,
corundum, carborundum etc.
The surfaces which are sanded
also generally contain soft
material , such as talc and
barium, to facil itate f latt ing.
Composition of
sandpapers
Sandpaper (technically speaking,
a flexible abrasive) is an
abrasive or flatting material,
which is made up of a flat
flexible support that could be
paper, cloth or vulcanised f ibres
and may even be plastic film and
minerals with very high
hardness levels , ground into
varying grain sizes according to
their use, are attached to the
support by means of different
layers of adhesive glue.
Abrasive minerals
The most common minerals
used in the manufacture of
abrasives are si l icon carbide
and corundum.
CORUNDUM is a very hard
mineral , whose bas ic
constituent is aluminium oxide
(Al2O
3) which is white in
colour in its pure form and
MAT E R I A L S F O R REPAINTING :AB R A S I V E S
I N T E R E S T I N G F A C T S
Hardness: physical property of
materials
Flatting consists in the elimination of
mater ia l by physical means.When
friction occurs between two materials
of different physical propert ies, one of
these will always wear into the other.
When materials of different hardness
rub together , the softer mater ial is
worn away by friction with the harder
one.
This property which resists wear is
known as HARDNESS . A mater ia l is
harder than another when it penetrates
it . A mater ia l is SOFTER than another
when it is penetrated by it .
There are various means of measuring
mater ia l hardness. The s implest method
was developed by the a geologist
named Mohs. It consists of a scale
made up of 10 minerals , arranged
according to their hardness, the f irst
one being talc which is the softest , and
the last one is diamond, which is the
hardest . Al l other mater ia ls wi l l be
classified according to which of these
10 materials it can scratch.
Mohs hardness scale :1.- Tal c
2 . - Gypsum
3 . - Ca l c i t e
4 . - Fluo r i t e
5 .- Apa t i t e
6 . - Fe lspa r
7 .- Qua r t z
8 . - Top az
9 . - Co rundu m
10 .- D i amon d
The flatting operations are essential to any repainting operation, and they
provide the superficial preparation for the correct adherence of the paint, and
also ensure the smoothing of the filler paints applied previously in the
areas repaired by the panel beater.
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could be rose or brown
coloured according to the
quantity of other substances it
contains.
SILICON CARBIDE (SiC) also
called carborundum is black in
colour with blue ir idescence. I t
is harder than corundum but it
is a lso more brit t le; th is means
that during its use , smal l
particles of crystals break off
and leave more sharp edges,
while corundum crystals have
more tendency to become
rounded with continuous wear.
To make the sandpapers, these
minerals are selected and
ground into grains of dif ferent
s izes , in order to achieve
different grades of paper.
The dif ferent grit s izes of the
grains wil l g ive us dif ferent
sandpaper grades. The EFAP
(European federation for
abrasive products) scale,
indicates the dif ferent s izes of
the particles by using a number
preceded by the letter P .
The higher the number, the
smaller the grit s ize on the
paper. The grade P12 for
example , corresponds to the
coarsest grade (therefore it
wil l have a very large grain)
and the grade P1200
corresponds to the f inest grain
(this wil l be have the smallest
grain s ize).
COMPOSITION OF SANDPAPERS
Abrasive mineral
Bonding
Flexible backing
CORUNDUM
SILICON CARBIDE
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When making sandpapers , the
choice of the abrasive grit ,
corundum, s i l icon carb ide , f l in t ,
etc. , depends on the type of
f latt ing which is to be done,
the hardness of the material to
be f latted, and the e f fic iency of
the f latting process , ambient
cond i tions e tc . In e f fect, the
use of the proper sandpaper
for each job is a guarantee of
maximum eff iciency.
The backing
Flexible backing is achieved by
the use of the materials already
mentioned previously, such as
paper, cloth etc. The thickness of
these materials determines the
flexibility of the sandpaper. The
backing material is chosen by the
manufacturer according to the
functions for which the
sandpaper will be used, the
type of surface and the
hardness of the material to
be flatted.
The bonding
Different types of bonding
material is used to fix the grit
to the backing, however these
can be divided into two main
types :
Organic glues Synthetic resins
The main organic glues such as
animal hide are made from
organic extracts. They are water
soluble and when the water
evaporates they bond the
abrasive grit solidly to the
support, however they have the
disadvantage of being affected
by water, in other words , when
placed in contact with water,
the adhesive deteriorates.
The synthetic resins used as
bonding material could be
phenolic resins, epoxy ureas
etc. and are generally
thermosetting or
thermohardening, therefore
water does not damage
abrasives made with this
type of bond.
The manufacture of abrasives
takes place in two stages, known
as bonding and orientating.
During the f irst stage, the grit
is fixed superficially to the
backing, and during the second
stage of glue application to the
entire surface, the grains are
orientated on the entire
surface.
The glues used in both these
stages could be different or the
same, and a combination of two
different glues could also be
used in both stages, depending
on the future use of the
abrasive.
I N T E R E S T I N G F A C T S
EFAP abrasive paper grades
The size of abrasive grit i s determined by
passing it through a sieve with a mesh
having a fixed number of holes per
square inch.This means that for a P80
grade paper, the sieve use d to separate
the grit has 80 holes per square inch, if a
sieve with 100 holes was used the grit
would not pass through.
The complete EFAP scale is shown in
order below, from the coarser grain to the
finest one.
P12
P16
P20
P24
P30
P40
P50
P60
P80
P100
P120
P150
P180
P220
P240
P280
P320P360
P400
P500
P600
P800
P1000
P1200
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Sandpaper manufacture
The most important aspect of
the manufacture of flexible
abrasive or sandpaper is the
way in which the grit is
deposited on the support. This
can be done in two different
ways:
Gravity deposition Electrostatic deposition
Electrostatic deposition ensures
a specific orientation of the
grain, and this orientation can
vary the behaviour of the
sandpaper. Another important
factor in the performance of the
sandpapers is the number of
grains placed on the surface.
Sandpapers with close coat
structure on the support have
grains placed over the entire
surface in a close pattern, and
abrasives with an open coat
structure have spaces between
the grains on the support. This
latter type of sandpapers
permits displacement of the
abrasive dust and therefore is
less prone to clogging of the
sandpaper.
It is important to select the
type of paper grain structure in
accordance with the surface to
be flatted and the clogging
tendency of the material on the
sandpaper.
Clogging of the sandpaper with
the dust from flatting is one of
the main causes of rapid
deterioration of the abrasives,
and for this reason, certain
products such as zinc stearates
are often added to provide
lubrication for the sandpaper
and facilitate evacuation of the
PLACING OF ABRASIVE MATERIAL BY DEPOSITION
ELECTROSTATIC DEPOSITION OF ABRASIVE MATERIAL
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residue, thus reducing the
tendency to clog.
The sandpapers are made with
dif ferent grain s ize, however it
is important to bear in mind
that this is not the only
measure of the quality of the
abrasive. A very important
aspect of the sandpaper quality
is related to the absence of
irregularly large abrasive grains
which could cause deeper
scratches than those expected
from the paper according to its
number classification.
Sandpaper
shaping
The procedures mentioned
above are those used to make
the sandpapers in huge rolls
which are generally not
employed in this form. The next
process is that of forming or
shaping the sandpaper by
perforation to produce the
shapes which we are most
accustomed to using, these
could be sheets, disks or rolls .
As well as the perforation of
the paper, it is also common to
find sandpapers with other
perforations which could serve
to permit the elimination of
flatting dust when fitted on
machines during the use of the
sandpaper.
SHAPE OF SANDPAPERS
Disk
Sheet
Roll
Different shapes of sandpapers used in
repainting workshops.
Perforatedsheet
Perforateddisk
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Basic concepts of
painting
In general we understand paints to
be varnish, enamel, lacquer, in
other words, a liquid substance,
with more or less viscosity, which
when is applied by different
methods on the surface to be
covered, solidifies by some process,
leaving an even layer firmly adhered
to the component painted.
When the paint applied to the
object being painted has
transformed into its final state
and can be called paint layer,
it will then provide the object
with the one or both of the
following qualities:
On the one hand it will provide a
protection against the elements
such as humidity, solar radiation,
heat, abrasion, various chemicals,
thinners, petrol etc.
On the other hand, it will
improve the beautification of the
surface being painted and even
out surface irregularities and
textures, and also give colour,
shine and diverse optical effects
to the surface.
For this reason we will talk about
the technical and aesthetic
aspects of paints when dealing
with the protective anddecorative aspects of painting.
Basic terminology
A very vast terminology exists
when it comes to describing
the different products known
as paints. We will talk here
below about the different
products used in one or another
form in the painting of
automobiles.
MAT ER I AL S F OR REPAINTING :PA I N T S
The application of paint provides a protective coating which can
increase the life of the component painted, and at the same time give it an
attractive finish thus enhancing its value.
RIMER
FILLER
STOPPER
LACQU
ER
ENAMEL
VARNISH
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STOPPER
PRIMER
FILLER
STOPPERS
The composite plastic type
products supplied in putty
form are known as stoppers
and can be applied with a
putty knife or similar tool.
Stoppers are designed to
cover up irregularities or
cracks in the base material.
PRIMERThis is the name given to a
liquid composition, with or
without added pigments,
which is used as the first coat
to cover up pores, give anti-
corrosion protection
and improve the adherence
of the paint layers which will
come after.
FILLER
This is a pigmented coat
which is appl ied to leve l
out smal l irregularit ies in
the surface to be pa inted,
in order to ac hieve an even
smooth surface ready to
receive the f ina l or f in ish
pa int coats .
ENAMEL
This is a paint which is known
for its ability to give a very
smooth finish.
VARNISH
This is the name given to all
liquid compositions, which
give a transparent film whenapplied in a fine and dry coat.
STAIN
This is a product which deeply
penetrates the substance to
which it is applied and
changes its colour. This is
normally a transparentsubstance in its pure state and
it does not form a coating.
LACQUER
This is a paint made basically
from organic colour
pigments which are soluble
in the binder, base or
organic composite. Its
main characteristic is itsvivid colours and it is more
or less translucent or
transparent.
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Paint composition
To enable the liquid substance
known as paint to carry out its
function of protecting and/or
decorating, it needs to be
composed of a series of
components which help it to
achieve this task. The basic
components of paint are:
BINDERS PIGMENTS
SOLVENTS
ADDITIVES
Binders
The binders or fixers are
substances which transform
themselves into solids once the
task of painting has been
completed. These are also
known as resins, and they are
the essential ingredients of
paints, s ince they carry the
remainder of the components
and additives, and for this
reason they are sometimes
technically known as the fixed
vehicle or non volatile
vehicle. The chemical nature of
the binders is in reality what
defines the characteristics of thepaint: its drying or curing
method and properties of the
finish coat regarding its
hardness, shine, resistance to the
elements, f lexibil ity etc. The
binder is also at the origin of
the name given to the type of
paint, thus acrylic paints are
made with a binder having an
acrylic resin base, cellulose
paints have cellulose binders etc.
Pigments
Pigments are very fine solid
particles and are insoluble in the
binder.They give different
properties to the paint, such as
colour and opacity.
Pigments are obtained by grinding
or crushing different organic or
inorganic materials. The
description pigments is taken
Binder
Pigments
Solvents
BASIC PAINT COMPONENTS
PAINT
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from the fact that the main task
of these materials is to add
pigmentation, although in reality
there are materials which are
used to make paints which are
added as pigments, but whose
tasks are completely different.
For this reason, we can list them
in the following families:
Anticorrosion pigmentsIncludes all those pigments
capable of providing an
anti-corrosion protection to
the base (steel, aluminium,
copper, etc.).
Extender pigmentsThese are opaque pigments with
a well defined and stable colour
which provide opacity and
colour or opaque and chromatic
effects, (due to their
composition and structure).
The first group of these
includes the traditional
pigments (red, green, blue, etc.).
The second group includes
aluminium and mica, which
produce metallic and pearl
effects.
Load pigmentsThese pigments on their own
have low extending ability, but
when combined with extender
pigments give body to the paint.
Specific action pigments
These are made from various
products which give specific
characteristics to the paint
such as:
Anti encrustation (for marineuse on boat hulls)
Fungicide effect for paints usedin areas affected by the
presence of micro-organisms.
Fire proof or fire retard effect.Etc.
SolventsSolvents are substances which
are added to the paint to
maintain the binder (or non
volatile vehicle) in a liquid state,
preventing its coagulation or
precipitation until the moment
of application. When the mission
of the solvent has been
accomplished, it evaporates from
the paint and does not form
part of the final paint finish.The
technical definition of the
solvent is known as a volatile
vehicle.
The paint may require more or
less fluidity depending on its
use, for this reason it may be
necessary to add more of the
volatile vehicle to the paint thanthat initially used for its
preparation. This volatile vehicle
is then called diluting since its
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I N T E R E S T I N G F A C T S
Paint additives
The high quality of a paint depends not
only on the quality of its basic
components and the excellent mixture
preparation, but also on the careful
formulation of the additives, without
which the paint will not conserve for long
or perform as expected. Some examples
of additives are given here below:
Hardening and drying: These have an
influence on the hardening and solidifying
aspects of the paint.
Texture: These additives modify the final
finish texture; surface roughness or paint
build.
Plasticiser:Mod ifi es the elast ici ty or
flexibility of the final paint coat.
Thickener: This improves the resistance
to peeling of the paint (tixotropic).
Wetting: Improves the dissolution of the
various components of the paint.
Dispersing: This avoids paint clogging
during storage.
Anti-sediment: These avoid solidification
of the pigments in the paint.
Emulsifying: These facilitate the mixing
of the paint components.
Etc.
PigmentBinder
Paint film
The solvents do not form part of the final
paint layer; they evaporate from the paintduring the drying process.
task is to dilute the paint. The
chemical composition of the
diluting may or may not be the
same as the solvent.
The main characteristic of the
solvents and dilutings is that of
keeping the binder in solution,
and their chemical composition
must be compatible with that of
the binder. Paints are generally
divided into two groups
according to the nature of the
solvents. These could be either
organic, meaning they are
formed of volatile organic
composites (VOC) like acetone,
benzene, butyl acetate and
these are known as solvent
based paints , or the other
group of paints, which use water
as the main substance in the
solvent and diluting, in this case
the paint is known as wa te r
based paint .
Additives
Despite the fact that the three
principal components of paint
are the BINDER, the PIGMENTS
and the SOLVENT, it is generally
necessary to add a range of
other substances which improve
or modify the characteristics of
the paint, and these are known
as additives.
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The paint drying method will define many of the characteristics of the
final paint layer.
PAINTS:
CLASSIFICATION ACCORDING TO THE METHOD OF DRYING
Paint drying
Paints can be classified
according to the nature of the
binder, based on different
criteria. An important aspect is
the drying, hardening or curing
process of the paint. With this
in mind, the paints used in
automobile repair can be
classified according to their
drying process:
Drying by solvent evaporation
Drying by oxidation
of the binder
Drying by a chemicalreaction between two or
more components
Drying by solventevaporation
This is the simplest of the drying
processes and involves drying of
the binder by evaporation of the
solvent.This dr ying could take
place with or without the
addition of heat to accelerate the
process. Obviously, if the paint
film comes into contact with the
solvents, these will be removed
by dissolving of the film.
Drying by oxidation of
the binder
This drying process not only
involves evaporation of the
solvent (similar to all drying
processes) but also a chemical
reaction in the binder due to its
contact with the oxygen in the
atmosphere.
This process could be assisted by
the addition of accelerators.
The chemical content of the final
DRYING BY SOLVENT EVAPORATION
DRYING BY TRANSFORMATION
(OXIDATION OF THE BINDER)
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paint coat is different from that
of the initial binder, for this
reason the film is rarely affected
by the action of the solvents in
the paint.
The drying phase could also be
accelerated by the application of
heat to speed up the evaporation
of the solvents.
Drying by a chemical
reaction between two
or more components
This process consists in the
production of a paint film as a
result of the chemical reaction
or polymerisation of
components, which are mixed
just before be ing used, when this
reaction takes place at ambient
temperature: when the products
are already delivered premixed
from the manufacturer, the
chemical reaction will take place
when a high temperature is
applied to the paint.
In the first case, only two
components are generally used,
and one of these is called resin
and the other is called
hardener, cataliser or
activator. Each one of these
components is supplied in
separate containers and they are
mixed when being used in precise
and accurate proportions. These
paints are known as 2K or two
pack paints.
In the second case, when the
reaction between the
components is only possible at
high temperatures, the product is
usually delivered already mixed
form the supplier. This paint is
known as thermohardening .
In all cases, the curing of 2K
paints can be accelerated by the
application of heat, which aids in
the evaporation of the volatile
substances. The paint film
produced with this process will
then have properties very
different from those before
curing: it will generally have very
high chemical and physical
resistance.
DRYING BY A CHEMICAL REACTION BETWEEN
TWO OR MORE COMPONENTS
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Repair shop operation
When a vehicle which has had
an accident arrives in the
workshop, the first task which
has to be done is the repair of
the bodywork: panel beating or
panel replacement. When the
panel beaters have finished their
work, the vehicle is then
transferred to the repair tshop
for repainting.
The repainting operation
protects the damaged parts from
corrosion, levels out the
irregularities produced by the
repairs and finally restores
the original colour of the
vehicle. All the above operations
can be divided into two
working stages, which are
known as:
Preparatory paintingprocesses
Finish paintingprocesses
Preparatory paints
The preparatory paints or base
coats are used to protect the
bodywork from corrosion, level
out the surface and prepare it
adequately for the application of
the f inal paint coats, which
under no circumstances should
be applied directly to the sheet
metal.
The preparatory or base coats
of paint used are generally of
the following types:
Stoppers
Primers Fillers
The final paint coats should be
applied on primers or fillers
which have been sanded with the
sandpapers, grade corresponding
to the final paint type to be used,
or on other paint layers also
sanded in the same way as for the
base coats.
Finish paints
The finish paint is the final
protection layer which is applied
to the vehicle and is therefore
the layer which is in contact with
the atmosphere. It should be
resistant to the sun, humidity,
abrasion, etc., and protect the
layers of paint underneath. At the
same time, since it is the finish
paint coat, its appearance plays a
vital role in the final quality of
the repainting job: the shine, the
colour and the covering
consistency will give the vehicle
its desired attractive finish.
This manual will cover the
preparatory procedures. The final
painting processes will be dealt
with in the manual no. 5.
Repainting can be divided into two stages:
- Preparatory painting whose mission is to level out and protect the surface.
- Finish painting which should restore the external appearance.
REPAIR SH O P REPAINTING PR O C E S S E S
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In order to ensure correct paint adhesion, the surfaces to be repainted
need to be thoroughly prepared: the cleaning, degreasing, removal
of rust and correct flatting are the basic preparatory operations
which need to be done.
Cleaning of the
vehicle
When a vehicle or parts of a
vehicle arrive in the repair shop
for repainting, the f irst and
most important job which has
to be done is a thorough
cleaning of these parts. Never
forget that it is also essential to
clean other parts of the vehicle
that may not need to be painted
but which could include dust
particles, and these particles
will be blown around when
using the spray gun and could
get stuck in the paint film.
We are talking basically about
the mud and dirt particles that
should be removed as much as
possible before starting to
paint.
When the above tasks have
been completed, adjoining parts
should be adequately covered to
ensure that these are not
stained during bodywork
repainting.
Removal of rust
Presently the majority of
automobile bodywork parts are
built with galvanised steel, when
the repair of these parts
involves the removal of the top
layers of paint, there is a risk of
corrosion, moreover if there is
a long delay between panel
beating and repainting. It is also
possible that the vehicle to be
repainted could have some
traces of corrosion, which
should be completely eliminated
before repainting.
The rust scales should be
removed by f latt ing. The
sandpaper grade should be
sufficiently rough to remove all
the rust but should not damage
the metal excessively by
reducing its thickness.
When the rust has been
removed, it may be possible that
some hidden traces still remain.
To ensure an efficient
anti-corrosion protection, it is
PREPARATORY PAINTING:PRE-TREATMENT OF THE SURFACES TO BE PAINTED
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necessary to protect the metal
with passivating agents
(treatment with phosphate acid,
zinc or similar products), which
practically stop the corrosion
process and create a protective
binding layer. These products
should only be applied to bare
metal or galvanised sheet, and
should never be used on
aluminium or other surfaces for
which they are not specifically
recommended.
When the passivating process
has terminated, the protective
primer should be applied
immediately, s ince otherwise the
effect of the passivator could be
completely contrary to that
desired, the maximum time
delay should be no more than
20 minutes.
Degreasing of surfaces
to be painted
To ensure that a layer of paint
designed to be applied on a
specific surface adheres
correctly, it is vital that there
are no particles or foreign
material which prevents the
proper contact between the
paint and the surface.
Normally the most common
problem on surfaces to be
painted is the presence of
grease , wax or oi l , and these
form a barrier between the
paint and the surface, which
causes adhesion problems. For
this reason it is very important
to correctly degrease the
surfaces to be painted.
Degreasing is done by using a
degreasing solvent which
should be spread over the
surface with a cloth steeped in
this fluid and only a small area
of the surface should be covered
since the solvent should be
removed form this area before it
evaporates
by using another dry clean
cloth.
The composit ion of the solvent
DEGREASER
DEGREASING OF THE SURFACE
The parts to be painted should be
degreased according to the procedure
described. Moisten the surface with a rag
dipped in the degreaser, and then before
evaporation, dry the surface with another
clean dry cloth.
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should be such that it is capable
of absorbing the contaminating
substances while at the same
time not damaging the surface
to be pa inted, and it should
have an evaporation time
suff icient to permit cleaning as
described previously. I f we
simply apply the degreaser and
leave it to evaporate from the
surface we will only move the
contaminants from one point
to another without removing
them.
Degreasing should be done not
only before painting, but also
before any flatting operation,
for the following two reasons:
1. A surface flatted with
contaminants causes the
formation of lumps when
mixed with the flatting dust,
which could cause
undesirable scratches on the
surface and deteriorate the
sandpaper.
2. The lumps cause the oil or
grease to penetrate to the
inner layers, from where it
could be very difficult to
remove them.
Preparatory f latting
To ensure that a paint adheres
properly to a surface , this
must not only be c orrectly
degreased, but a lso have the
correct roughness for the paint
which wi l l be appl ied. This is
achieved by the use of a
sandpaper with the adequate
grit s ize for the job.
However, these two operations
of degreasing and f latt ing
cannot be done properly on
panels which have undergone
panel beat ing , s ince they wi l l
have areas with sharp
separation l ines between areas
which have paint and bare
metal.
In these areas where the
surface is not f lat , i t wi l l be
dif f icult to do proper
degreas ing and f latt ing, and an
orbital sander wil l have to be
used with a abrasive paper
grade of P80 or P100 to give a
feathered edge to the
transit ion zone between the
paint and the bare metal.
FEATHERING EDGES
Before After
The feathering of the edges facilitates the
formation of an even surface with littleirregularities and permits the execution of
an optimum painting job.
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Bare metal priming
When doing a repainting job, it
is important to try (with the
best use of available technology)
to offer the maximum anti
corrosion protection, as close
as possible to factory painting,
where the bodywork receives an
optimum anti-corrosion
protection.
One of the prime factors in this
process is the use of protective
primers on those areas of the
bodywork stripped to bare
metal, where they wil l have lost
the cataphoretic protection
applied at the factory.
Two basic ty pes of pr imers are
used in repainting, and these are
classified according to their
chemical composition as
follows:
Phosphate primers Epoxy primers
The primers also have to have a
perfect bind to the metal and at
the same time serve as an
optimum base for the adherence
of the paint coats which will be
applied later.
Phosphate primer
The phosphate primer also
known as wash primer
complies with the above
requirements. It is usually
2-pack and its useful life or
Pot Life when mixed is
24 hours at 20 C, which means
that it can be mixed and kept in
the gun throughout the day and
used when required, and then
emptying and cleaning the gun
at the end of the day.
The only inconvenience with
this type of primer is that it is
not possible to use polyester
stoppers over it . This is due to
the fact that non hardened
stopper affects the chemical
composition of the primer and
causes peeling. On the other
hand, it should be pointed out
that it is possible to use this
primer on top of polyester
stoppers since in this case the
stopper will be dry and
chemically inactive and have no
effect on the pr imer.
When the metal to be painted
does not need the application of
stoppers and can be levelled
with the use of surface fillers,
phosphate primer is the best
choice for protection.
The filler used to cover the
primer should be applied when
the wash primer has dried but
still retains its binding power.
The phosphate primers can be
flatted when they are perfectly
The phosphate primers or wash primers and the epoxy primers
are the most commonly used by repair shops for
anti-corrosion protection.
PREPARATORY PAINTING :AP PL IC AT IO N O F PROTECTIVE PRIMERS
I N T E R E S T I N G F A C T S
Pot Life
This is the term applied to the working
period available for a mixture. With a two
pack or (2K) paint, the mixture of the
resin and the cataliser is usually done just
before use, and the chemical composition
could affect the workable time of the
mixture.
The paint can spread and will have
acceptable adherence within the pot life
period specified for this mixture and
when this period, indicated on the
manufacturers specification sheet, has
been exceeded, the paint should be
discarded.
Drying time
The drying time of a paint is the time
since its application when the paint film
has formed and the part can be
manipulated. Hardening is progressive and
is thus divided into various stages:
Dust proof dry: at this stage, the dust nolonger adheres to the paint. The part must
be handled with care since the finger
pressure could mark the surface.
Refit dry: the part can now be refitted, butnote that very strong finger pressure will
leave marks, since the paint is not yet
completely hardened.
Final dry: the part can now be used for itsfinal purpose, or it can be flatted.
Binding power or wet on wet
application
When paint has been applied and it is
still not fully dry or hard, it will still retain
its binding power.This means that another
layer of paint can be applied on top
without the need for flatting, this process
is known as wet on wet or W/W. When a
paint layer has lost its binding power, it is
necessary to lightly scuff the surface to
ensure good adherence.
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dry, i f need be, to e l iminate any
small defects or if they have
been on too long and require
flatting to ensure adherence of
the next coat. The best choice
for this is to use dry flatting
paper with a P400 grade.
The evaporation time between
coats is usually about 5 minutes
and 2 to 3 coats can be applied
if required. The drying t ime at
20 C before filler can be
applied is about 30 to
90 minutes.
Epoxy primers
Primers with epoxy resin based
binders have the advantage over
the previous mentioned primers
in that they are resistant in any
thickness when applied on top of
polyester stoppers and they can
be applied in thicker layers,
making it possible to use them
as fillers. Their disadvantage in
relation to phosphate primers is
that they need a long drying
time in the region of 4 hours at
20 C.
A good option is to use these
primers on bare metal when a
small area has to be repaired
with the aid of stoppers. This
avoids having to apply the
stoppers directly on the bare
metal.
FillerEpoxy primer
PRIMER APPLICATION
Polyester stopper
Metal
Filler Phosphateprimer
Metal
Polyester stoppers can be applied on
top of epoxy primers but this is not
possible with phosphate or
wash primers, and it is onl y
possible to apply fillers on phosphate
primers.
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Polyester stoppers
Polyester stopper is a paste
composit ion and is applied by
us ing a putty knife . I t is a
2-pack paint which should be
mixed just before use : one of
the components being the
res in , and the other, the
cataliser. To prepare the
mixture , the correct amount of
cataliser indicated by each
manufacturer should be added
to the paste . This is usua l ly
about 2 to 3 grams of cataliser
for each 100 grams of paste; in
other words about , 2 % to 3 %
in weight.
These components should then
be well mixed until it is not
possible to dist inguish the red
colour of the cataliser, (for this
reason it is coloured red) , and
thus a perfect mixture wil l be
achieved. The pot l i fe of the
stoppers is very short , about 5
to 10 minutes , and when this
period is exceeded, the stopper
will have hardened on the putty
kni fe , therefore the appl icat ion
should be fast and precise,
eliminating all traces of stopper
from the knife and cleaning
these with common solvent.
The amount of stopper mixed
should only be suff icient for
application in this short space
of t ime and could even be a
l i t t le less , s ince as t ime passes ,
the stopper gets more and
more di f f icult to work, and
loses its adherence.
Application of
stoppers
The areas which have been
repaired by the panel beaters
need to be laid bare at first and
then degreased and sanded and
only then can polyester stoppers
be applied to level the surface,
removing the undulations and
roughness left after the panel
beating hammers and dollies and
any other tool employed in this
process. Polyester stoppers
permit the removal of
deformations in precise points
where this is necessary and
The polyester stoppers should be used in a controlled fashion, since
if excessive thickness of stoppers is used to compensate for a shoddy panel
beating job, this will lead to poor paint quality later.
PREPARATORY PAINTING :AP PL IC AT IO N O F STOPPERS
I N T E R E S T I N G F A C T S
Catalisation of polyester stoppers
The mixture of the cataliser and the
hardener for stoppers should be done
using the proportions specified and these
should not be altered under any
circumstances since this could seriously
affect the paint process:
If too little cataliser is added....The stopper will not dry in the specified
time, flatting will be difficult, the sand
paper will clog up and the surface will
be marked and scratched.
I f too much cataliser isadded.. . .
The stopper will not harden faster than
normal, but some residues of active
cataliser (organic peroxide) will remain
and this will react with the pigments of
the fillers and final coats when these
have been applied on top, changing their
colour and creating stains and shades.
PREPARATION OF POLYESTER
STOPPERS
CATALISER
STOPPER
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impossible to achieve with the
use of sprayed surface fillers.
To ensure good quality repair it
is necessary to moderate the
thickness of stoppers applied:the repaint quality starts
with the pane l bea te rs
wo rk. The thickness of the
stopper when flatted should not
be greater than 400 to 500
microns to ensure a high quality
repair.
Polyester stoppers should only
be applied strictly where needed
and then using the minimum
quantities and trying to shape
the profile with a scraper as
much as possible. This ensures
than the subsequent flatting
takes less time: spending a
little more time in the
application of stoppers will
help to reduce the time
required for flatting .
Polyester stoppers can be
applied directly to degreased
and sanded sheet metal,
although it should be taken into
account that they may be
formulated for application on
sheet steel only. In this case
they will have poor adherence
on galvanised steel and
therefore polyfunctional
stoppers which adhere
perfectly to sheet steel and
galvanised steel should be used.
Another option is to apply the
stoppers on top of a primer
layer(this should be epoxy)
which will provide greater
anti-corrosion protection.
I N T E R E S T I N G F A C T S
Preparat ion o f po lyester
s to pper s
The most important points to bear in mind
when preparing stoppers are:
The stopper mixture in the can should bewell homogenised with the help of an
agitator before removing the amount
required with a putty knife, since the solids
could percolate down and the resin will float
on top. If the can is not well stirred, the
stopper taken out could have more resin or
solids than normal and the mixture with the
cataliser will not have the specified
proportions( the reaction takes place
between the resin and the cataliser and the
solids take no part). This not only means
that the mixture will have the incorrect
proportions but also the material remaining
in the can will be affected since it will have
a different proportion of solids and resins
than originally intended.
Do not place any tool or knife in the canwhich is not perfectly clean, and above all
these should not contain any cataliser or
mixed stopper (which contains cataliser),
since when cataliser comes in contact with
the resin in the can, a chemical reaction will
take place, and although this may be slow, it
will reduce the quality of the can contents.
Only polyfunctional stoppers
will adhere directly to
zinc tre ate d stee l.
PaintZinc treatment
Steel
Stopper application area
Polyfunctional stopper
Standard stopperStopperapplication
options
APPLICATION OF STOPPERS ON ZINC TREATED STEELS
B2-29
31
Epoxy primer
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Flatting of stoppers
The drying time and hardening
of the polyester stoppers is
short, thus making it possible to
flat them after a short period.
However it is important to
allow this short drying period
of about 30 minutes at
20 C. With very low
temperatures it is advisable to
wait for 40 to 45 minutes.
A incomplete drying of the
stoppers will lead to defects
when flatting similar to those
produced by incorrect
catalisation.
The surface of the stopper
could have sticky extrusions of
material caused by residues of
resin, causing clogging of the
f latt ing paper; to avoid this
effect it is sufficient to clean
the surface with cleaning
solvent, this wil l enable faster,
easier and more efficient flatting
to be done.
The flatting of polyester
stoppers can be superficial and
it not necessary to use fine
grade paper, s ince it wil l need
to painted with a filler or base
coat before applying the final
coat. For this reason it is
possible to use medium to
rough grade paper, thus
speeding up the flatting process.
Paper grades of P80 to P120
are the most adequate to start,
and the finishing off should be
done with a P240 grade to
cover the marks made. Sanding
can be done manually withblocks or planes or by using
sanding tools, however water
should never be used to
facilitate the process, polyester
stoppers should always be
dry flatted , s ince due to their
composition th ey retain water,
and this will be covered by the
layer of paint. This could cause
blisters on the surface when
curing the final coat of paint
caused by evaporation of the
water retained in the stopper.
The presence of water in the
paint layers will also lead to the
appearance of corrosion points.
The most adequate tools
recommended for flatting
polyester stoppers are orbital
sanders with a hard base for
use on large f lat surfaces, while
rotary orbital sanders should be
used on irregular surfaces.
When flatting of the stopper
has been completed on an area,
it may be necessary to reapply
more stopper when a lack of
material is noticed in any point;
in this case, the excess f latt ing
residues are removed with
compressed air, dilutings and
rags, and the process of
The flatting of stoppers presently used in repair shops should be done
dry, the use of water in this process will increase the risk of corrosion
and subsequent paint defects.
PREPARATORY PAINTING :FLATTING OF STOPPERS
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stoppers application is started
over again. In genera l , th is
process should not be repeated
more than twice.
To do an excellent job, it is agood idea to protect the areas
which could be damaged or
dirtied during the application of
stoppers. The cost of the
protective material and the time
required to place it on can be
compensated by the time
required to do unnecessary
cleaning of the bumpers,
mouldings , s idel ights etc. , as
well as the additional risk of
causing damage to these items.
When the stoppers application
process has been completed,
the next job is the application
of a surface filler as well as a
primer on those areas of the
sheet metal which has been left
bare. The surface f i l ler should
completely cover the stoppers
and must therefore be applied
to an area larger than the area
of stoppers, and this area must
be previously flatted to ensure
proper adherence. This f latt ing
should never be done with the
same paper as that used for
f latt ing the stoppers, s ince it
could cause excessively large
crevices which may be partially
covered by the surface f i l ler, but
will later reappear when flatting
again and the final paint coats
will not hide these marks.
The flatting of the perimeter
area adjoining stoppers is
known as feather edge
flatting and this should be
done with a fine grain paper.
The best method for this job is
to use an abrasive sponge
known as Scotch Brite U.F. or
V.F., manually or by using a
sander to flatt an area of 15 cm
wide around the stoppers.
B2-30
Stoppers flatted(grade P220)
Area to be flatted(abrasive sponge)
FEATHER EDGE FLATTING
AROUND THE STOPPERS
33
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Task of surface fillers
Surface fillers are base or
ground coat paints with a dual
task: on the one hand they must
smooth out the zone which has
been repaired, and on the other
hand they must provide a
perfect base for the final coats
applied later, so that these can
develop all their qualities of
coverage and shine.
The final paint cannot be
applied directly on the stoppers
or primers, s ince they do not
offer sufficient surface
quality and could cause the
appearance of paint absorption
problems (sinkage), loss of
g loss, e tc .
The composition of the surface
fillers is usually of the acrylic
2K type similar to the single
layer paint, which offer the best
preparatory paint quality.
The surface fillers should be
used to cover the stoppers and
primers.
Types of surface fillers:
solids content
The surface fillers are designed
to do a finer job of surface
levelling not possible with
stoppers alone, due to the
thickness of the dry paint film
available with surface f i l lers. For
this reason, surface fi l lers are
known according to their filler
abil ity, in other words,
according to the maximum
thickness which can be
achieved. Since this thickness
relies on the composition of the
filler and more specifically on
the solids content, this gives
rise to the designations known
as STANDARD, MS and HS,
which correspond to:
STANDARD, standardsolids content
MS, medium solids
content
HS, high solids content
Types of surface fillers:
methods of
appl ication
Wet on wet fillers
One of the application
methods used for f i l lers is that
known as wet on wet which
is usually indicated by the
symbols W/W. With this
method, the f i l lers are used
solely as an intermediate or
sealing layer between the
stoppers and primer and the
f in ish coat , without trying to
achieve a level l ing e f fect , and
the f inal paint coat is appliedwhen the f i l lers st i l l retain
their binding power (when
wet).
The surface filler is the paint which will act as a base for
the subsequent finish coats of paint, which should only be applied on
the correct base or on existing finish coats.
PREPARATORY PA I N T I N G :AP PL IC AT IO N O F SURFACE F I L L E R S
Binder
Binder
Loadingpigments
Coveringpigment
Solvent
Solvent
2K
ACRYLIC
FILLER
2KSINGLELAYERACRYLIC
ENAMEL
The basic difference between the
2K acrylic fillers and the 2K finish
paints (single layer enamel) is in the
type of pigmentation.
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Sandable fillers
This is the most common
method of fillers application,
where the fillers are allowed to
dry completely and are then
flatted.
Tintable fillers
Another important application of
the filler paints is that of
providing a base paint with a
colour tint similar to the final
coat, so that this can be applied
with the least number of passes
possible, while at the same timegiving correct coverage.
The coloured fillers can be
formulated by the addition of
specific quantities of the finish
coat colour, making it possible
to prepare these as required
with the colour desired.
Formulation of the
surface fillers
In general any filler product can
be used in different forms
according to the combination of
solvents, catalisers and additives
used and the mixture
proportions of the final product.
In other words, the same base
product can be used as a
standard, a HS or MS or wet on
wet filler etc.
It is important to decide on the
type of filler to be used
according to the temperature
conditions during its application,
and choosing a fast filler when
the temperature is below 18 C
and a medium filler when the
temperature is between 18 C
and 25 C, and a slow f i l ler
when the temperature is above
25 C.
An important factor in the use
of fillers is the Pot Life or
useful life of the mixture, which
generally oscillates between
30 and 60 minutes for acrylic
f i l lers. For this reason, only
prepare the quantity required
for immediate use.
REPLACED PANELS STANDARD OR MS
SMALL REPAIRS TO PANELS MS
PANELS REPAIRED HS
INTERNAL PARTS H/H
NORMAL FINISH QUALITY H/H
HIGH FINISH QUALITY FLATTABLE
POOR COVERING COLOURS TINTABLE
WHAT TYPE OF FILLER SHOULD BE USED?
Characteristics of the parts to be painted Filler to be used
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Filler application
The surface fillers are applied
with a spray gun on the area
required: either on a complete
part or panel, as in the case of
replacement, or large panel
repairs, or on a specific part
of a panel, to cover a small
deformation, or to cover the
application of polyester
stoppers.
Each type of filler requires a
different spray gun nozzle and a
specified pressure adjustment,
which is generally between
3 and 4 kg/cm2.
The utilisation of HVLP (high
volume low pressure) spray guns
improves efficiency of filler use.
The ideal place to apply filler
paint is in the spray booth,
especially if the area to be
covered is large. However, a flat
platform with extraction
facilities could be sufficient,
especially if it is fitted with an
overhead extractor cowling.
Moreover, if a HVLP spray gun
whose spray diffusion is much
less than normal guns is used,
the difficulties associated with
compressed spraying outside the
paint booth can be largely
overcome. A point which should
not be overlooked when applying
fillers is the need to do a good
masking job of all surrounding
parts, in order to avoid the need
for later cleaning of windows,
panels and mouldings which have
got paint stains.
As in the case of all paints, it is
vitally important to respect the
flash off times, and with medium
or high density fillers, this is
crucial since it directly affects
the drying quality of the paint
job.
The flash off times between paint
coats will be between 5 and
PARTIAL FILLER USE
Stopper Filler
The filler should be applied in such a way
that it covers all the stoppers and primers
used. In the case of small damages,
it is not necessary for the filler to cover
the entire area since the present paint
provides a good base for the application
of the finish coat.
COMPLETE COVERAGE WITH FILLER
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When applying filler, care should be taken to
ensure that each successive layer remains
within the area covered bythe previous paint, this prevents coverage of
areas with filler dust which could show up
later when flatted.
10 minutes, depending on the
thickness of the coat applied.
When dealing with fillers used to
provide surface levelling
(sandable fillers), it is common
practice to use several layers in
order to completely cover the
damage, and more layers should
be used directly on the damaged
zone. For example, on localised
panel repair, it is normal to apply
more filler paint to the area
repaired with stoppers than on
the surrounding area.
The filler layers should always be
applied, by starting to apply paint
to the widest area and then
gradually moving into the centre,
to the area which requires the
heaviest layer, the opposite
should never be done. The reason
for this order of application is
that after applying a paint layer to
an area with stoppers, some
stopper dust will be dusted out
to the edges.When this area is
covered with the following layer
of filler paint and subsequently
flatted, some stopper dust will
come to the surface, and this will
form a very poor base for the
following finish coats and could
lead to shrinkage and sinkage of
the paint.
SprayedShrinking will be created when
the finish layers are applied
INCORRECT APPLICATION OF SUCCESSIVE FILLER LAYERS
Sprayed CORRECT APPLICATION OF SUCCESSIVE FILLER LAYERS
37
Flatting
Flatting
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Flatting of fillers
It is very important to carry out
a proper flatting of the fillers,
since the final paint coats will be
applied to this surface, and
blemishes will show as a clearly
visible defect.
Fillers should only be flatted
when they are completely dry,
especially when they are thick, in
which case they often appear dry
on the surface but internally they
may not be so, and when flatting,
the damp filler could be reached
and then large scratch marks will
appear and the abrasive paper
could clog.
The drying time of fillers at
20 C varies between 3 and 12
hours according to their nature
and the layer thickness applied.
During the flatting operation, two
phases can be distinguished:
Rough flatting Fine flatting
in the first of these, the rough
flatting is intended to adjust the
surface to the same plane as the
panels. Rough grade abrasives are
used.
The task of the fine flatting is to
prepare the surface quality of the
filler so that the final paint layers
will adhere perfectly and be
capable of covering up the flatting
marks. For this reason, finer grade
paper is used.
The lighter the layer of filler
applied, the less the work of rough
flatting which has to be done.
Wet and dry flatting
Fillers can be wet or dry flatted,
although presently it is more
advisable to choose the dry
method, since it gives the same
surface quality results as the wet
method and in less time.This is
mainly due to the fact that the wet
flatting has to be done entirely
manually, creating a lot of dirt,
while the wet flatting method can
be carried out with sanders which
are generally fitted with dust
suction heads.
Wet sanding is generally associated
with use of finer grade paper than
dry flatting, since the presence of
water accentuates the action of
the abrasive.
Progressive flatting
This flatting method consists, as
mentioned previously, in a
progressive flatting process,
starting with the roughest grade
I N T E R E S T I N G F A C T S
Comparison between wet and dry
flatting
Different types of abrasive are used for
the flatting of fillers depending on
whether this is done wet or dry.This is
due in the first instance to the fact that
the abrasive has to withstand contact
with water and also depends on the tool
used.
Tools used for dry flattingElectric or pneumatic sanders and
sanding blocks.
Tools used for wet flattingSanding blocks.
Since the cutting power is greater whenwet flatting, the grain of the abrasive
used can be smaller.
The comparison of the sanding paper
grade when wet flatt ing wit h manua l
blocks and dry flatting with rotary
orbital sanders are as follows:
Rough flatting:
Dry : P220/P240 and P320/P360
Wet: P320/P360 and P500/P600
Fine flatting for single layer paint:
Dry : P400
Wet: P 1000
Fine flatting for dual layer paint:
Dry : P500
Wet: P 1200
To ensure that the final paint coats can develop all their shine
and covering qualities, as well as the absence of sanding marks in
the repaired area, it is essential to carry out a proper
flatting process of the filler.
PREPARATORY PA I N T I N G :FL AT T I N G O F F I L L E R S
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paper and finishing off with the
finest grade, leaving slight marks
which can be covered by the
finishing paint coat. However, it is
not possible to pass from the
rough grade paper directly to the
finest one, since the difference in
the grit size will be too much,
making it necessary to use one or
more intermediate grade papers.
The main reason for this process
is that the difference between
one grade of paper and the
following should not be too great,
otherwise the finer grade paper
will only scratch the peaks of the
ridges left by the rough paper.
During a progressive flatting
operation, it is possible to remain
within acceptable quality limits by
using a sandpaper up to three
grades finer on the EFAP scale
(page 14) than the previous one.
Final flatting for single
or dual coat finish
paints
The final flatting of the surface
filler paint is different depending
on the type of finish coat to be
applied, since a single coat finish
will be thicker than a dual coat
finish (if we discount the
thickness of the varnish, since this
is transparent and will not be able
to hide the marks left by the
flatting process), the single coat
finish on the other hand can cover
the majority of the deep flatting
marks.
ABRASIVES
P80 P150 P240
PROGRESSIVE FLATTING
INCORRECT PROCEDURE CORRECT PROCEDURE
Surface to be flatted Surface to be flatted
1st Flatting with P80 1st Flatting with P80
2nd Flatting with P80 2nd Flatting with P240
2nd Flatting with P150
3rd Paint application 4th Paint application
FLATTING MARKS CAN BE SEEN NO VISIBLE FLATTING MARKS
A goo