Hairline scratches
Magnified paint surface scratches
Types of Paint Surface Scratches
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).
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 -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 out without leaving very fine scratch marks.(See also Wipe Down Process)
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.
• 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.
Removing more that 0.5 mil (12µ) 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.
Grit Numbers
Sandpaper or finishing paper is the most common item from a larger group of products known as "coated abrasives" i.e. Aluminium oxide. When talking about "grit" is a reference to the number of abrasive particles per inch of finishing paper (sandpaper). The lower the grit the more abrasive and conversely, the higher the grit number the lesser (smoother) the finishing paper
When talking about abrasive finishing paper, "grit" is a reference to the number of abrasive particles per inch of paper. It eliminates the risk of deep sanding scratches by providing a uniform grit size. This makes sense if you imagine how small the grit particles on a 1000-grit finishing paper would need to be to fit into a 1- inch square. Grit finishing paper is referred to by the size of its abrasives (i.e. 1500-grit paper) the grit you use depends on what you are trying to do.
Foam pads - are also rated on a grit number, that is to say the scratches they will remove after using grit finishing paper along with a similarly rated polish (i.e. 2500 grit rated pad and polish combination will remove the marks left after using 2500 grit finishing paper)
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.
Both foam pads and polishes have a grit number) most polishes will state the level of scratch removed by stating grit numbers i.e. will remove 2000 grit scratches caused by using 2000 grit finishing paper
Once you have identified the scratch ‘grit’ marks you can match a polish and a foam pad (i.e. 2500 grit marks, require a polish that is capable of removing 2500 grit (number) marks, matched with a suitable cutting pad (e.g. Menzerna Power Finish (PO203S) this is a one-step scratch remover polish that will remove 2500 grit, matched with a LC White light cutting foam pad)
1. 1000 < grit Heavy - (Compound) levels and removes heavy defects
2. 1200 grit Heavy - levels moderate to heavy defects
3. 1500 grit Medium - levels light to moderate defects
4. 2000 grit Moderate - levels light defects and removes hazing
5. 2500 grit Light - levels swirl marks, light defects and removes hazing
6. 3000 grit Fine - very minor corrective ability, burnishes paint to high gloss
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