2 Conceptos de Pintura - La Preparacion

8/12/2019 2 Conceptos de Pintura - La Preparacion

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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


APPLICATION OF PROTECTIVE PRIMERS 28-29


APPLICATION OF STOPPERS 30-31


FLATTING OF STOPPERS 32-33


APPLICATION OF FILLERS 34-37


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.


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.

7


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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


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.


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

15


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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

17


18/44

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.


19/44

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

19


20/44

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


21/44


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.

21


22/44

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)


23/44

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

23


24/44

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


25/44

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

25


26/44

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.


27/44

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.

27


28/44

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


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.


29/44

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.

29


30/44

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


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


31/44

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.


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


32/44

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


33/44

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


34/44

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.


35/44

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

35


36/44

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


37/44

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


38/44

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


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


39/44

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

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2 Conceptos de Pintura - La Preparacion