Abrasives and Polishing

[togwt]

An abrasive [: is a material, often a mineral, that is used to shape or finish through rubbing which leads to part of the surface being worn away. While finishing a material often means polishing it to gain a smooth, reflective surface]



A difference in hardness between the two substances: a much harder abrasive will cut faster and deeper, grain size (grit size): larger grains will cut faster as they also cut deeper. Any liquid or paste that contains an abrasive, however fine or soft will leave scratch marks on a surface, which may not be visible to the naked eye. This is also the case with detailing towels, micro fibre or 100% cotton will leave micro scratches as they are both abrasive due to the material and weave used.



A polish used on automotive paint is an example of an abrasive suspended in a liquid, paste or wax, as are some polishing liquids for chrome and other bright metals. The liquid, paste or wax acts as a binding agent that keeps the abrasive attached to the cloth or foam pad, which is used to as a backing to move the abrasive across the surface



Polishing and Waxing are very different and should not be confused, although the retail industry has blurred them together in marketing. This is not generally possible because the substances perform separate functions; in general terms a wax is used for protection and a polish is abrasive and used for surface correction. The word ‘polish’ is used because when you apply wax to a vehicle you are ‘polishing the car to a shine’



[Detailers] A polish is an abrasive product that removes imperfections and levels a surface to enable the light to reflect evenly.



[General public] The word shine is also used in the context "I polished with a wax to make it shine" hence the confusion between the two.



Abrasives Composition



Abrasives are made from chromium oxide, aluminium silicate, zirconium silicate and carbides; their abrasive ability depends on the shape of its 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 paint



When a silicon-free polish is used to eliminate surface scratches it works on the surface of paint using aluminium oxide spheres, suspended in water and hydrocarbon oils and a mechanical friction process to abrade the surface of the paint down to the level of the bottom of the scratch.



Liquid or Paste Polish



Liquid polishes tend to perform better because they allow you to use the oxidation you`re removing as an abrasive. Paste polishes tend to be harder to wipe off, especially if they are allowed to dry. They can leave a large amount of white residue in small grooves or cracks. Liquid metal polishes dry to a powdery residue which is much easier to remove, and the fast acting formulas (containing mild abrasives) perform to the same or higher level than typical paste formulas.



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.



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.

Diminishing abrasives require friction - not heat (that is just a by-product of kinetic friction) to activate and progressively reduce their size until they become a finite milled dust; they are buffered or cushioned in a lubricating water-based oil film emulsion, usually in a semi-liquid paste.



Wet polishes eliminate the friction induced heat caused by buffing; heat causes gloss loss. Some very abrasive compound polishes don’t feel abrasive to the touch because the particles are formulated in a solvent or polymer oils in a water-based emulsion and are not released without friction.



The abrasive start off as large particles, which removes the most paint, they are then reduced in size into finer and finer particles (hence ‘diminishing’) removing progressively less of the paint surface, by the friction caused by the foam pads contact with the paint surface. By varying the size of the abrasive a differing cut is obtained, so the more the abrasives are reduced in size the finer the resultant finish until the particles are reduced to a very fine powder, which in turn produces a burnished surface shine.



The amount of size reduction (diminishing) can be adjusted by the type of abrasive material used (silica and /or aluminium oxide) allowing some polishes to used for the removal of surface scratches only, but if required can then followed up with a finishing type polish that contains smaller abrasives. Were as some polishes will remove surface scratches and by changing the abrasive ability of the foam pad will then go on to buff the surface to a shine ready for the application of a last step product (LSP)



Polishes are a very essential product for the overall appearance and condition of the paint finish. There are abrasive polishes formulated to remove paint finish issues such as oxidation or other paint surface imperfections such as surface scratches.



Light polishes contain either mild abrasives and / or a chemical cleaner (solvent) most mild abrasive polishes will remove medium scratches or surface imperfections, whereas a strong abrasive compound polish rely both on a chemical cleaner (solvent) l and mechanical abrasives to rectify more serious paintwork issues.



Lessen the Need for Polishing



Proper washing and drying techniques are the best way to avoid the need for polishing. Using a chemical paint cleanser versus polishing on a clean finish to simply remove old wax/sealant is another. And always follow the rule of using the least abrasive polish and pad combination (working smarter not harder)



Related Articles



1. “Difference between Diminishing and Standard Abrasive Polishes� - http://www.autopia.org/forum/autopia...ml#post1472658



2. Before you Start Machine Polishing - http://www.autopia.org/forum/autopia...polishing.html



3. “Surface preparation prior to polishing� - http://www.autopia.org/forum/autopia...ml#post1489935



4. “Clear Coat Thickness and UV Protection Removed by Polishing� - http://www.autopia.org/forum/guide-d...ml#post1448231





[Edit: Definition added 09.05.12]

[Accumulator]

Note also that some products contain "abrasives" that are so mild as to be *functionally* nonabrasive on most automotive paint, at least in a practical sense. They often help make said products more user-friendly, especially in the sense of easy wipe-off. Just because a product "contains abrasives" that doesn`t mean that it`ll behave abrasively on your paint and/or that it`s a product to avoid if you`re concerned about thinning the paint.

[togwt]

Accumalator- I see the point your trying to make. I wrote this with a view to explain `Abrasive polishes` to neophytes

[Accumulator]

TOGWT- Yeah, I just figured it was perhaps useful supplemental info that might as well be included here in case somebody is studying up on this stuff.