Most Common Causes of Paint Surface Scratches

From DetailingWiki

Most common causes of scratches to a paint film surface

Scratches (cause)

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

•Placing or dragging an object across the trunk lid

•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 insufficient lubrication when using automotive detailer’s clay

•Improper methodology / tools used when washing paint surface. This is the most common cause of surface scratching / marring) Detailers tend to categorize scratches as "swirls" but technically there are two types of scratches due to the differing methods used to impart them onto the paint surface

1. Halo-scratches, which, when the light reflects off the raised edges of the scratches, appear as circular scratches (hence halo) 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 and others can be rather deep into the clear or top coat.

2. Swirl marks or holograms - (sometimes referred to a buffer trails) this type of scratch has a fine pattern, caused by the use of a high speed polisher and not using a finishing product / pad

•Surface scratch (or marring-) probable cause is by automatic car wash or poor cleaning techniques. The marring makes light 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 mildly abrasive 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 a mild / mediumn 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.

Before deciding upon treatment, you should first access how deep the scratch is and how badly the paint film surface is compromised. A surface scratch that will `catch' your fingernail is approximately 0.004" deep will usually require either a high-speed rotary polisher or wet-sanding and refinishing (best undertaken by a professional or an experienced detailer) most polishes will state the level of scratch removed by stating a grit number

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

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) a temperature of 115 oF< will cause the paint to soften), and thickness, i.e. how much of the surface are you removing

Reference source

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