Paint Surface Scratches (Cause
& Effect) Repair
Before you start to polish you need to
ascertain your client’s detailing goals, for his vehicle and how realistic they
are.
Be cognizant that what your eyes ‘see’
is very different to theirs, you are probably a little OCD about the results
you want to see. Your goal may be 85% + scratch free, which you will inspect
with all manner of lighting and a trained eye.
For most owners they just want a clean
shiny surface and a paint protection product that has a reasonable durability.
They have no idea that you remove scratches
by replacing then with finer and finer scratches that can no longer be seen by
the naked eye, removing scratches also entails removing paint and there is only
a finite amount you can remove until the paints protection is compromised.
As a trained ethical professional you
should discuss your clients detailing goals and educate them on how they can be
accomplished. Once you have built trust in your abilities they will want you to
look after their vehicle, repeat clients, that’s one of your most important
business goals, isn’t it?
Once you have established trust they
will want their friends and relatives to have you take care of their vehicles;
win / win.
Paint hardness
More accurately, density, can be
affected by a number of factors including the composition of the clear coat
used, single stage, clear coat (BC_CC) or powder coated) and how it is applied.
There is a trade-off to be had at the manufacturing stage between scratch
resistance and gloss levels against oven drying time and temperature, along
with the quality of the isocyanates (products designed to add gloss and
accelerate paint hardening times). Low paint density can also occur if the base
colour coat is not allowed sufficient hardening time before the clear coat is
applied. In order to better understand the relevance of density / hardness it
is necessary to compare some examples of well-known items; to compare them a
scale is required. So, given the definition of ‘hardness’ is a material’s
relative resistance to deformation, scratching or penetration,
Types of Scratches
The less you physically
touch the paint surface the less likely you are to cause scratches. Most
surface scratches are caused by improper washing or drying, or by using
unsuitable media. Avoiding paint scratches (as
much as is possible) will lessen the need to use an abrasive polish along with
the subsequent loss of clear coat
Scratches in the clear coat or its
sub-surface, that is to say any form of damage that is in the top layer of the
paint surface, which includes; marring, swirl marks, scratches, stone chips,
water spots and acid etching. The most common form of sub-surface damage is
caused by road thrown stone chips, particularly on the front ends of cars.
Surface scratches are invariably caused by grit being trapped between the paint
surface and the applicator and being moved across the surface under pressure
Most scratches on a paint
surface are V or U shaped, being caused by a small sharp object (fine sand or
grit) and a slightly blunt object (belt buckle, button or zip) so an abrasive
polish and pad are more readily able to polish the sides and smooth the points
where the top of the scratch meets the surrounding paint's uppermost surface
(paint levelling).
What
makes a scratch visible is that it makes the paint surface two-dimensional and
the light reflects from the microscopic peaks and valleys differently from the
rest of the paint surface. When you abrade an area with a machine and foam pad
these abrasions form a uniform pattern (the machine /foam pad applies an even
and consistent pressure) and light reflects from its surface evenly without any
two-dimensional reflectance giving the impression that it’s been ‘removed’
The perfect, mirror-like
reflection of light from a surface, in which light from a single incoming
direction is reflected into a single outgoing direction the best example of spatial reflection is seen when
reflected from a flat level surface.
If the surface is perfectly
flat, light will be reflected to produce a mirror image of the surface. But if
there you have matte paint or are imperfections such as swirls, surface
contaminants, orange peel, or oxidation (dull, opaque or unlevelled paint)
light is refracted and the reflected light becomes distorted, diffuse reflection, which mutes the
shine.
Technically we have different types
of scratches because of the different ways they are introduced into the paint.
·
Surface marring –could be in either in the paint surface or wax /sealant, the shallow surface marks often caused by
the incorrect use of a micro fibre towel, improper washing methodologies or the scratch pattern caused by a dual action polisher. Surface
marring is actually made up of tiny scratches, which can easily be remedied by
using a very light abrasive one-step polish
·
Halo-scratches - (swirl marks or
spider webs) which, when the light reflects off the raised edges of the
scratches, appear to be circular but in reality they are made up of numerous
straight line random scratches which are caused by washing, drying and everyday
wear and tear. Some are surface marring, whereas others can be deep into the
clear coat.
·
Holograms - (also called
buffer marks or buffer trails) which again are scratches but these scratches
are micro-fine patterned scratches which are caused by a high speed polisher
and an operator who doesn't know how to properly finish down their work. They
take on a 3D effect and if the car is moving or you move around the car they
seem to "flow" through the paint.
·
Pig-tailing - caused by
dried compound residue lodged in the fibres of a wool pad
· Etching - is a type of paint defect that can vary in depth and frequency, but
creates a unique pattern dependant on how it is created. Etching is caused by
chemical reaction (Acid Rail, IFO, Bird excrement, bombs, and the residual
minerals found in water) on that paint’s surface that dissolves the surface,
creating depressions.
· Deep Scratches- a surface scratch that will `catch' your fingernail is
approximately 0.04 Mil (1.0 ยต) deep will usually require wet sanding
· Haze - this is usually caused by using a pad / polish combination that
is too abrasive for the paint surface to finish without leaving very fine
scratch marks. Paint exhibits a general lack of gloss, this could also be
caused by harsh detergents, solvents, or hardly perceivable hairline scratches
or even a paint protection or polish that is not properly removed, all of which
leave behind a dull surface that doesn’t reflect light.
· Surface scouring – this is usually caused by abraded paint residue not the pad or
the polish used
·
Swirl marks - Swirl
marks (buffer trails) ribbon-like abrasions, the things that cause swirl marks
are varied; an unnecessarily aggressive pad or abrasive, excessive speed or
pressure used or too stiff a backing plate are just some of the many reasons
for this type of surface defect. Even scratch-resistant and ceramic clear coats
are susceptible to swirl marks if polished incorrectly.
·
Stone chips - and
other minor damage are not only aesthetically displeasing they look unsightly
and once they begin to accumulate, especially on dark coloured car. But worse
still, because the stone chips, scratches and scuffs have penetrated the clear
coat, your car will be prone to rust
Cause and Effect
Too ensure a near
perfect paint surface blemishes need to be removed. However, there are some things
to be cognizant of as it is possible to actually make things worse by using
improper methodologies.
Proceed with this
in mind; always choose the least intrusive product, it is preferable to polish
2-3 times to restore the paint film surface than to use an unnecessarily
abrasive machine polish / foam pad combination. Before commencing polishing do
a test panel on the car, once you have achieved the desired results with your
selected polish / pad combination then proceed to polish the rest of the panels
·
Foam pad - using a foam pad that
is too aggressive or is not suitable for the polish selected
· Polish - select an abrasive
polish to match the scratch you are trying to remove; by using the least
abrasive combination of polish / pads to remove the defect, before moving up to
a more abrasive combination. It makes no sense to use a very aggressive polish,
that will remove most scratches but to the detriment of the clear coats
thickness. Know your product and its capabilities before using it.
·
Dirty pads - will become
more abrasive, as will pads that are simply sitting in a dirty or dusty
environment. Even microscopic dirt and dust on a pad can lead to swirl marks.
·
Cross contamination- do not use
the same pad to apply differing products as cross contamination; i.e. a pad
that was used with a polishing compound may have traces left and if the same
pad is use for polishing it will cause scratches. However, if you thoroughly
clean pads right after use you shouldn’t have any problems with contamination
from different grades of polishes or compounds.
·
Backing plate - a hard and
inflexible backing plate will affect the performance of a foam pad; by making
it slightly more aggressive (stiffness) and may cause swirl marks. The
inflexible plastic on many backing plates has zero give and therefore will not
adjust to the contoured body panels. The exception would be a plate bonded to a
thick layer of dense cellular foam.
·
Speed - using too high a speed
will not necessarily get the job done faster as there is a risk of instilling
swirl marks or strikethrough, which will need to be corrected to remove
·
Pressure - excessive pressure will make the pad / polish
combination more aggressive, this has the effect of increasing kinetic energy
(friction heat) which may result in a strikethrough, a friction paint burn or
paint delamination from the substrate.
Increased surface friction will also cause swirl marks
·
Heat - excessive heat and a combination of excessive pressure (surface resistance) speed
and an aggressive pad / polish combination will rapidly generate surface heat,
this will soften the paint and may cause delamination from the substrate,
surface hazing, strikethrough and greatly increase the chance of swirls.
·
Pad angle – ideally a pad should
be operated flat to the surface; this provides the correct contact surface area
along with sufficient surface lubrication from the polish oils. By turning a
pad on an angle you reduce the surface are contact, increasing pressure and
reduce the amount of surface lubrication available. Incorrect polish techniques
will lead to swirl marks.
·
Insufficient product - without the polish
lubrication oils, dry buffing will cause delamination from the substrate,
surface hazing, strikethrough and greatly increase the chance of swirls.
Common causes of scratches
•
Improper methodology / tools
used when washing or drying a paint surface. This is the most common cause of
surface scratching / marring) and accounts for as much as 75% + of surface
marring
•
A large proportion of all
paintwork scratches are caused by automated car washes. Minute particles of
hard materials, such as road dust and sand, become lodged in the rotating
brushes and etch scratches into the paint surface. These “hair-line” scratches
are particularly noticeable in darker paint shades.
•
Using an unsuitable
applicator or brush to clean the vehicle or remove snow etc.
•
Using cheap micro fibre or
terry cloth towels or some wash sponges will scratch the paint as these
materials are hard and unforgiving, inflicting scratches without the need for
grit particles
•
Placing or dragging an
object across the boot lid
•
Jewellery (rings, bracelets,
etc.) coming into contact with paint (i.e. rings abrading door handle recess)
•
Using too much pressure with
a car duster on a dusty / dirty surface
•
Pulling a car-cover over a
very dusty / dirty vehicle or dirt /grit on the inside of the cover
•
Wiping a dry surface with a
dry cloth
•
Infrequent rinsing of brush
or wash mitt when washing vehicle
•
Using a dirty towel (dirt /
grit trapped in fibres) and / or applicators that contain polyester (plastic)
threads
•
Using a towel or cloth that
is unsuitable for paint film surfaces
•
Not thoroughly rinsing road
grime before drying
•
Using a car wash concentrate
that doesn’t suspend grit / dirt before it gets rinsed away
•
Improper use of a
water-blade (i.e. not rinsing blade surface after each pass)
•
Wiping a spot of dirt / dust
with your hands to maintain a ‘pristine’ look
•
Using an unnecessarily
abrasive automotive detailer’s clay and / or insufficient lubrication
Paint Surface
scratches
•
Visible damage-if the
scratches show a black, grey or white colour it probably means that it's
compromised the paint system through to the primer. They can usually be
rectified by thoroughly cleaning the affected area, then apply a rust
preventative primer before the application of both a colour and clear coat with
a solvent or a slightly abrasive pre-wax cleaner or polish. Re-apply a
protective polish and sealant after the repairs have been affected and the
paint has had time to cure.
•
Visible abrasions- dragging
an object across the top of the trunk lid often cause this kind of surface
damage, or careless use of the car keys or even fingernails around the door
handles. They can usually be rectified with a slightly abrasive pre-wax cleaner
or an abrasive polish.
•
Surface scratch (or marring-) most
probable cause is by automatic car wash or poor cleaning techniques. The
marring looks like thousands of tiny single directional uniform scratches that
cause light to refract instead of reflect, this kind of damage is usually confined
to the clear coat, and can usually be rectified with a pre-wax cleaner or
polish.
Deep Scratches
A surface scratch that will
`catch' your fingernail is approximately 0.04 Mil (1.0 ยต) deep will usually
require wet sanding and the clear coat refinishing Removing a scratch requires
removing the layer of paint that contains the defect; you need to level the
paint to the lowest point of the scratch.
Removing more than 0.5 mil (12ยต) of clear coat will cause premature
paint film failure as UV protection percolates to the top of the clear coat.
Check paint film thickness with a Paint Thickness Meter (PTG) before you
attempt to remove
As you go over a deep scratch, the
abrasives round off the edges of the
high spots of the scratch. The result is a shallower scratch (when no full
correction can be made) rounded edges don’t reflect light the same way a sharp
edge will and is therefore less noticeable.
Unfortunately, a more and
more common form of deep scratch is those inflicted with a sharp object i.e. a
key. It may be necessary to carry out some localized wet sanding to facilitate
full removal of any deep scratches, once again, paint thickness must be
checked, and if the paint is too thin wet sanding should not be considered
Backlighting
Clear coated paints
show minor swirls and scratches more readily than pigmented paint (single
stage) due to an optical effect called backlighting. Light penetrates the clear
coat and is reflected from pigmented paint (colour coat) which in turn reflects
any imperfections in the surface of the clear coat, making them highly visible.
As you
drive towards the setting sun or oncoming headlights on a rainy night, every
speck of dirt, smudge or smear on your windshield is suddenly very obvious.
They are much more noticeable when sunlight or oncoming headlights back-light
them.
Removing surface scratches with a
machine-
Removing a scratch requires
removing the layer of paint that contains the defect; you need to level the
paint to the lowest point of the scratch. The dual action of a random orbital
motion will require more applied pressure to work the compound into the scratch
as opposed to the singular action motion of a rotary spinning with less applied
pressure. Due partly to its indirect application of pressure; it removes more clear by putting an
uneven pressure on the abrasives
a) A
dual action polisher’s orbital’s operating action (throw or offset) is not as
efficient at transferring the energy required to create the kinetic friction
required, because it puts an uneven pressure on the abrasives. It spins on a
double axis, resulting in a pretty much "random" motion of a single
point on the pad. This simulates the "random" motion of hand
application of polishes.
The
downside of this is that you cannot abrade the clear coat either to remove
scratches. The PC pretty much just smoothes over the tops of the scratches, not
really sanding away any measurable clear coat. To remove scratches, you have to
make multiple applications to see a visible improvement. So for these reasons a
random orbital polisher removes more paint than a rotary circular polisher to
remove the same surface defect
b)
With a high-speed rotary polisher - you will be removing a
certain amount of clear coat and actually levelling the surface. This is good
because you truly remove the scratches, not just making them less refractive to
light, as the PC does. The problem is that you only have about 1.5 or 2 mil (50
ยต) of clear coat to work with.
A
rotary polisher requires less pressure and its circular motion is a more
directly applied force is very efficient and will remove more paint for each
polishing step, which is usually 2-3 to remove surface defects. Its rotational
action is able to focus kinetic friction on the high spots the paint more
efficiently.
c) Using a moderate to light polish; and
utilizing a rotary polisher will remove approximately 0.000025 - inches (0.635
Microns) from the paint surface (they are many variables such as
polish/compound and speed / pressure used that may affect the paint removed)
You seriously have to make a judgment call about whether any defect is so
severe that you cannot live with it and therefore it is worth risking clear
coat failure to remove it with the rotary
d)
Block or wet sanding (finishing paper and a sanding block) is
the most efficient process for paint scratch / defect removal. A polish or
compound applied by the sanding block with constant pressure applied to
maintain a flat even surface contact. Because of its linear process you abrade
the paint surface until the scratch or defects are removed.
Note
1.
It is preferable to polish 2-3 times to restore the paint film
surface than to use an unnecessarily abrasive polish / foam combination
2.
Wool pads are not recommended for random orbital machines
(Porter Cable 7424, etc.) as wool pads nap / fibres works more efficiently with
a centrifugal motion Foam cutting pads tend to be much’ stiffer’ than wool
fibres and thus will transfer the movement of the machine to the paint surface
more efficiently than a comparable wool pad on an orbital polisher
3.
Natural wool is most aggressive - 50/50 wool/acrylic blends
intermediate - lamb’s wool the least aggressive
4.
Always use the least aggressive product first, and then
evaluates the surface, then only if necessary `step-up' to a more abrasive
product and / or pad.
Levelling paint
When
a detailer uses the term "levelling paint" it really means that they
are going to be abrading the surrounding paint area that that contains the
defect (scratch, swirls, surface marring, etching, pitting, etc.) So they are
not ‘removing the imperfection’ just making the surrounding edges of the
scratch flat. It is possible to remove a scratch by using a high-speed rotary
and abrading the clear coat to a lower level then the base of the scratch,
which will remove clear coat, just be aware of how much clear coat you remove,
as you don’t want to compromise the paint systems protection.
Removing more than 0.3 mil (8ยต) of
clear coat will cause premature paint film failure as UV protection percolates
to the top of the clear coat, there is UV protection all the way through the
paint, but the majority of it rises to the top with the thinner solvents and
particles. As a point of reference a sheet of copy paper is 3.5Mil (89ยต) a
surface scratch that will `catch' your fingernail is approximately 0.004 Mil
(0.01ยต) deep will usually require wet sanding and refinishing.
Modern
clear coat paints are formulated from polyurethane, applied as a
microscopically thin ‘elastic’ film, 1.5 – 2.0 Mils, too much friction heat
will cause it to expand, driving the scratches deeper into the paint surface.
Always be aware of paint surface temperatures (localized paint temperature
should be limited to 110.oF.
In accordance with the Society of Automotive
Engineers (SAE) study a temperature of 115.oF< will cause the paint to
soften), and thickness, i.e. how much of the surface are you removing (See also
Paint Thickness Gauge)
Light Surface Marring
The light surface
marring that result from wiping down with a towel or the scratch pattern caused
by a dual action polisher Surface marring is actually made up of tiny
scratches, which can easily be remedied by using a very light abrasive one-step
polish (Menzerna PO 203 S - Power
Finish) and a protective wax
and/or polymer sealant. This way you’ll maintain the original paint’s integrity
for decades, with allowance only for environmental erosion.
Methodology
1.
Wash the paint surface
2.
Bonded contaminants on the cars paintwork should be removed
using a detailer’s clay bar to leave a smooth surface ready for machine
compound or polish.
3.
Throughout all stages of the polishing process the cars trim
adjacent to the area being worked on should be carefully protected using
painters tape to mask it to avoid damage. Protect sunroof seal, headlight covers, lighting rubber seals,
windscreen surround, pant edges, vehicle emblems and model identification
numbers, etc.
4.
Whenever you’re removing painter’s tape from automotive paint,
always pull back on the tape at an angle as a safety precaution.
5.
Start the polishing process with a diagnosis of the paint finish
and then proceed with the least aggressive polish / pad combination on a ‘test
section’ panel, once you have established a suitable polish/pad combination
proceed to polish / refine the paint surface
6.
It may be necessary to carry out some localized wet sanding to
facilitate full removal of any deep scratches, once again, paint thickness will
be checked, and if the paint is too thin wet sanding should not be considered.
7.
Finally use a polish to remove any surface imperfection and then
a fine polish / pad to burnish the paint surface
8.
Carry out a wipe down process to ensure all oils and surface
defects have been removed.
9.
Re-wash to remove any polishing dust and / or debris
10.
The final step could be to use a glaze, pre-wax cleaner or go
right to protecting your paint with a sealant and/or wax.
I
would like to think that these articles become an asset to anyone who is new to
detailing and to professionals alike, as well as industry experts who seek to
advance their knowledge.
I hope the above article was
informative. By having some understanding of the ‘What’ and ‘Why’ as well as
the ‘How’ along with a little science to help you understand how the chemicals
we use react, you can achieve the results you desire.
I would appreciate it if you
would share this article as it helps other detailers further their knowledge.
Questions and/ or constructive
comments are always appreciated.
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2012 TOGWT® (Established 1980) all rights reserved
