Graphics by TH001 (Todd Helme)
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 µ) 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.
A surface scratch that will `catch' your fingernail is approximately 1.0 µ (micron) 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 0.3 mil (8µ) 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
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 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.
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.
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 0.3mil (8µ) 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 (89µ) a surface scratch that will `catch' your fingernail is approximately 0.004 Mil (0.01µ) 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.
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.
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