Surface Science: Car Scratches
As any driver knows, surface scratches plague the visual aesthetics of a car’s paint job. They make a paint finish look dull and neglected, and in some cases can cause the need for repainting. What most everyday drivers don’t know is that there is a science behind scratches, and removing them isn’t as easy as a simple wax or machine buff makes it look. Many people fall victim to thinking their paint is in pristine condition simply because it’s been recently detailed, only to wind up disappointed a few months later over their car’s newly visible scratches. It’s important to understand that not every scratch can be removed, but all scratches can be made less apparent to the human eye.
WHAT IS CLEAR COAT
Clear coat refers to the clear top layer of paint that is applied over a colored base coat, and is found on most modern cars. Clear coat increases the paint’s durability, gloss and resistance to harmful environmental effects such as UV rays; similar to a more permanent wax. Typically – and it varies by manufacturer – clear coats are 1.5 to 2 mils in depth (50 – 60 microns). To give you an idea of how thin this really is, 1 mil is 1/1,000th of an inch. As you polish, you’re taking off and removing microscopic amounts of this clear coat, and according to some manufacturers, there are limitations to the amount you should be removing. Here’s what the American companies say is the most you should never remove from your car’s clear coat:
- Chrysler: .5 mils (12-13 microns)
- Ford: .3 mils (7-8 microns)
- GM: .5 mils (12-13 microns)
IDENTIFYING A SCRATCH
The basis of scratch science begins with depth. The depth of a scratch will determine whether it can be simply buffed out or has to be painfully repainted. If you were to examine a scratch as part of a cross section, you would notice the surface’s different layers: most commonly metal, primer, color, and clear coat (Figure 1). There are many different types of scratches and identifying their differences is the first step back to a lustrous finish.
- Level 1A: A minor clear coat scratch is the easiest to take care of and is the most common type of scratch. These are left by almost anything coming into contact with an unprotected surface, even a dirty towel. These are harder to see simply because they’re not too deep, and are easily fixed without causing major harm to the clear coat (ie. hand polishing or light buffing).
- Level 1B: The deeper side of clear coat scratches aren’t as easily taken care of, but can be effectively removed or reduced by proper machine polishing and rounding. 1B scratches are most commonly related to swirl marks and are caused by automatic car washes, poor technique, dirty applicators, or neglect. These are noticeably deeper than 1A scratches, but haven’t hit the paint.
- Level 2: If you’ve noticed a scratch and you can’t see another color behind the pigment of your car, you can be sure you haven’t hit primer or metal. In this case, say the scratch has gone through the clear coat and into the paint itself; the color is still good, so touch up paint will not be necessary. These are similar to clear coat scratches, other than the fact that you’ve actually taken a bit out of the paint. Since you’ve pierced the paint layer, level 2 scratches cannot be fully removed, but can be polished down to an almost unnoticeable level.
- Level 3: If a scratch is into the primer, but not the metal, you’re still not going to be able to get it out, but you will be able to make it a lot less visible. At this depth you’ll usually see white or an off-white (even grey) color beneath the paint, signifying that you’re at the primer level. Although you shouldn’t have to worry about rusting at this depth, you should still take action. In this case, use touch up paint on the scratch as soon as possible.
- Level 4: If the scratch has hit the metal, you’re going to have to repaint or use touch up paint. At this depth you’ll see a silver color when examining the scratch, and, if left untreated, the surface will slowly transition to a rust. Neither waxes, glazes, or polishes will be able to fix a scratch that has punctured the metal, no matter what any “magic” product promises. If this situation has occurred, clean out the scratch immediately and grab some touch up paint as soon as possible
Unfortunately, the world of automobile enthusiasts has deemed machine buffing the ultimate answer to any problem regarding paint. With no offense to the community, this is absolutely wrong if you’re interested in preserving the health, beauty, and longevity of your finish – think vintage cars with original paint. If you’re more of the 3-year lease type and your car has a predetermined lifespan, by all means polish away, but it’s important to realize that proper care can prevent the need to dig into your car’s clear coat in the first place. Also, if you’re set on machine buffing, remember that each time you take a machine to the surface, you will either be removing some clear coat or subjecting your paint to swirl marks.
Preservation begins with a mindset. Truly caring for your car’s paintwork is keeping it properly protected throughout the years, and this proves to be rewarding. As stated earlier, the less of clear coat you remove, the better job you’re doing at protecting the paint. The basis of preservation rests on filling rather than cutting, and keeping the largest amount of factory clear coat on the car as possible. This doesn’t mean that polishes and glazes are to be avoided, but rather the types of products need to be understood. Smoothing polishes and fine polishes are gentle on clear coats, and when used with a finishing glaze, help to fill and slightly round the edges of the scratch – making them less noticeable. Preservation successfully minimizes the appearance of all scratches, even level 4, by limiting the amount of light reflection within a scratch. The rougher and deeper a scratch is, the more light reflects inside the scratch, making it increasingly visible to the human eye (Figure 2). Although hand polishing will do just fine, preservation doesn’t necessarily mean no machines, but rather than a high speed or rotary model, an orbital buffer is preferred for this process.
Correction is the more aggressive polishing technique and is usually referred to as common practice within the detailing community. Also recognized as high speed buffing, cutting, machine polishing or fixing, correction utilizes more abrasive technology to remove clear coat scratches (1A). The amount of clear coat removed will vary depending on how deep the scratches are that you’re trying to get out, but always remember that the more you buff, less and less clear coat is left to protect the painted layer. By cutting, this process will successfully remove level 1A scratches and some 1B scratches from the paint. Although deeper scratches (level 2-4) can only be shortened and rounded, this process minimizes their visibility by allowing light a direct path of reflection. For paintwork correction processes, leveling compounds are used and utilized in stages – usually a more abrasive compound followed by a slightly less abrasive product, and finished with a glaze before waxing. Similarly to the preservation process, the finishing glaze is used to further smooth and fill any last imperfections after leveling compounds have been used – this helps to provide an even surface for wax application and minimizes the appearance of any deeper scratches that may not have been removed by the compound.
For at-home and professional detailers alike, the importance of understanding and identifying (Level 1A, 1B, 2, 3, 4) surface scratches should never be understated. In the detailing world, paintwork correction and paintwork preservation are both techniques and mindsets that can be incorporated into any buffing procedure. For example, correction techniques may be used on some deeper areas, while preservation is used on the rest of the car. Combining the two comes with expertise, time and practice, but can prove rewarding at the end of the day. Becoming knowledgeable on the sciences behind clear coats, scratch depth, and polishing procedures will lead to smarter car care and, most importantly, a better looking car.
But here is what my opinion about. NO matter how good we remove the scratches. NO matter how good we flat down the layer of clear coat for nice look. NO matter how good we keen to protect the car paint with sealant... We as a daily driver, NO matter you go to work to school or anywhere you go.
None of us can avoid sand blow to us when we are driving, whereby sand and stone chip will still keep on hitting our car body.
Even we are putting in a super highclass and super duper hard coating which claim almost perfect protection among environment...
reduce much polishing and scratch/swirl removal, put wax and sealant more frequent as good habit. Forget about compound unless you got a deep scratches that make you feel uncomfortable....what say if you just compound-ed yesterday and today got another scratches hit...good luck for your car detailing journey~!