Basics of abrasive polishing

 

Basics of abrasive polishing

Automotive paint surfaces comprise numerous microscopic peaks and valleys, much like the profile of a mountain range. These irregularities are known as capillary structures; there may be millions of these defects per square inch.

When these scratches are removed from a surface it becomes a smooth level surface that reflects light. Scratches are identified by a grit number; "grit" is a reference to the number of abrasive particles per inch of finishing paper that are required to remove the scratches left by the grit scratches i.e. 2000 grit scratches are removed by using an abrasive rated at 3000 grit. You are actually replacing scratches with even finer scratches until they are invisible to the naked eye.

Menzerna manufacture a range of abrasive polishes from 1000 grit all the way down to 4000 grit (SF4000) these polishes contain nanotechnology ceramic micro particle diminishing abrasives that are milled to 0.3 µ (micron) They mill their own abrasives, which allows them to control the size and uniformity of the aluminium oxide abrasive used and also contain a higher abrasive content, 7% were as the other polishes contain 3% abrasives.

The abrasives are just one factor in the equation; lubricants, solvents, emulsion and their carrier system will determine the actual functional ability of the polish. Diminishing abrasive polishes are pad ‘dependent’ as far as its paint correction / renovation abilities are concerned. These polishes were designed to work by utilizing kinetic (or dynamic) friction to break-down the diminishing abrasives, the more friction applied to diminishing abrasives the finer they become; this is how even micro scratches are removed. It works on the surface of paint using aluminium oxide spheres, suspended in water and hydrocarbon oils and a mechanical process to abrade the surface of the paint down to the level of the bottom of the scratch.

Abrasives

The ability for a polish to "cut" depends on the shape of its crystals or particles, not necessarily its size. A medium size, spiked abrasive will tumble and dig. However, a large round crystal won't leave a deep scratch.

Aluminium oxide has a hardness factor MOHS 9 and will not break down during polishing. Rather the larger clusters of aluminium oxide reduce in size. A large hard abrasive may also be brittle. It will cut once and lose its edge, while a softer small abrasive will hold its edge and keep on cutting. Many smaller abrasives have wedge shaped edges protruding from triangular crystals. These can easily slice through an oxidized layer of paint

Types (Grades) of Polish

A surface scratch that will `catch' your fingernail is approximately 0.04 Mil (1.0 µ Microns) deep will usually require wet sanding and refinishing. Other than that > 1000 grit scratches can be removed with a polish/compound and a machine polisher.

The ability for a polish to "cut" depends on the shape of its crystals or particles, not necessarily its size. A medium size, spiked abrasive will tumble and dig. However, a large round crystal won't leave a deep scratch. A large hard abrasive may also be brittle. It will cut once and lose its edge, while a softer small abrasive will hold its edge and keep on cutting. Many smaller abrasives have wedge shaped edges protruding from triangular crystals. These can easily slice through an oxidized layer of metal.

Liquid polishes tend to perform better than pastes because they allow you to use the oxidation you're removing as an abrasive. The oxidation will be no coarser than the abrasive in the polish, and since aluminium oxide is second only to a diamond abrasive, it makes an ideal cutting compound.

1. Compounds

Are the most aggressive, most abrasive type of polish and will remove the largest amount of clear coat in the shortest period of time. Compounds are commonly used on severely neglected vehicles and to clean up wet sanding marks. Compounds will almost always leave behind some marring, hazing, or holograms and should always be followed up with a finer polish or multiple polishes.

2. Abrasive Polishes

Most polishes that correct moderate paint imperfections fall into the category of an abrasive polish. They are a step below compounds in terms of aggressiveness and usually do not finish down as well as a finishing polish. On most paints, it is recommended to follow up an abrasive polish with a finishing polish to remove any micro-marring, hazing or holograms as well as increase the depth and gloss. Some abrasive polishes are capable of finishing on certain paint.

3. Finishing Polishes

A finishing polish will remove very minor imperfections in the paint, such as micro-marring, hazing and holograms. A finishing polish is formulated with a very mild abrasive that finely polishes the paint surface and effectively enhances light refraction and reflectivity. They are also used to burnish (jewelling) the paint to achieve an exceptional level of gloss and depth.

4. Paint Cleaners

A chemical paint cleaner are designed to enhance the depth and gloss while properly preparing the paint for a sealant or wax. Sometimes paint cleaners can have micro abrasives or they can be non-abrasive. They typically will not remove imperfections that require levelling the clear coat, but can remove some oxidation and mineral deposits.

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 the chosen polish / pad combination proceed

 

 

Amount of polish

I’m certain you’ve all heard the mention of two pea-sized drops on a pad as the correct amount of polish to use.  Now this will work, but not as a starting point.

If you rub a dry pad against your hand, you will notice that very soon your hand gets hot. Be cognizant that each foam pad will have a degree of mechanical cut of its own. A pad without polish can be quite dangerous, easily overheating and burning the paint. My recommendation is to apply a liberal amount of polish to the fresh pad. Then carefully massage it into the face of the pad – often referred to as ‘priming the pad’.

Apply a proper amount of compound, massage it in and get ready to polish. Although this may sound wasteful, this can make all the difference when you actually start polishing:

• All polish will have its own lubrication (oil, wax, polymers or a combination of these) which also helps the pad to run cooler and avoid overheating the paint, which will suit many of the new paint systems that manufacturers are using today. It’s much safer too, especially when working delicate areas like edges because they usually have a thin coat of paint and the extra lubrication may prevent strikethrough or burnt paint

• The whole surface area of the pad is now working, properly cutting for you. No hot/cool areas that could cause problems and inconsistent results. The theory is quite simple; a primed pad is like a piece of sandpaper used for wet-sanding, with the abrasives evenly spread out and it has adequate lubrication.

• Using a primed pad with two dime-sized drops of polish after each polishing stage, clean and re-apply polish to the pad, trying to keep the pad evenly coated with polish ready to polish the next section.

Why is a clean pad so important to the process?

Clean and / or replace pads as often as is necessary; a clean seasoned pad will enhance the abrasive abilities of the compound / polish and make the process not only more efficient but less time consuming. 

The best way to clean a pad is by using compressed air hooked up to a high velocity nozzle. If this option is not possible then brush the pads frequently with a nylon brush while the machine spins the pad. This is important to keep the fibres from matting down as well as prevent contaminated abrasives from clumping together and marring the surface.

Lastly - DO NOT over polish paint; there is only a finite amount of clear coat available