Common Causes of Paint Surface Scrathes

From DetailingWiki

The most common causes of scratches to a paint film surface are:

•Improper methodology / tools used when washing 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 scratches” are particularly noticeable in darker paint shades.

•Using an automated car wash or using an unsuitable applicator or brush to clean the vehicle or remove snow etc

•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) or towels 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 or insufficient lubrication

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. What makes a scratch visible is that it makes the paint surface two-dimensional and the light reflects from the microscopic peaks and valley’s 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’

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)

•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.

•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.

•Visible damage-if the scratches show a black 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. (See also Section 13)

What makes a scratch visible is that it makes the paint surface two-dimensional and the light reflects from the microscopic peaks and valley’s 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.

Note: To remove minor scratches by hand- use Meguiar’s ScratchX and a terry cloth applicator.

Removing surface scratches with a machine-

a) A rotary orbital buffer- 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. It has the advantage that no heat is generated, so you cannot burn your paint. 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 and pits, not really sanding away any measurable clear coat.

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. 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

Information resource -

• "Automotive Detailing Inside & Out, A Knowledge Base for the Perfectionist"– by Jon Miller