What The Differences Are Between Compounds, Polishes, Glazes And Chemical Paint Cleaners?

Preparation, preparation, preparation... is the key to achieving amazing car care results. No matter how good your fancy wax is, or how many coats of it you apply, you will not achieve a perfect finish unless you spend time preparing your paint properly. Proper preparation involves two key steps. In the first, firmly bonded surface contaminants are removed using tar removers and detailing clay, to leave painted surfaces feeling perfectly smooth. In the second, sub-surface defects sitting below the paint surface are removed by polishing, which is a broad term for a range of processes that remove or mask paint defects and enhance surface gloss in preparation for the addition of protection.

The polishing step is often skipped or misquoted by many car care enthusiasts (in the latter case we mean that many people often say they have polished their car as a catch all term for whatever they have done to it). This may be because they do not fully understand what polishing does, or because they are not confident enough to try it, or because they believe it requires equipment that they do not have. As a result, many enthusiasts are left dissatisfied with the appearance of their paint. In this guide, we will attempt to shed some light on the subject of polishing by (i) illustrating common sub-surface paint defects, (ii) describing the different types of polish currently available on the market, (iii) demonstrating how to polish paint by hand and (iv) demonstrating how to polish paint by machine.

What do we mean by sub-surface defects? Sub-surface paint defects are any forms of damage that are cut into the uppermost layer of paint on your car, and include marring, swirl marks, scratches, stone chips, water spots and acid etching caused by bird droppings and bug remains. By far the most common form of sub-surface defect is stone chips, particularly on the front ends of cars. However, many paint finishes also suffer from swirl marks and etching, and scratches are almost guaranteed if you park in supermarket car parks on a regular basis. Another less common form of defect is buffer trails or holograms, which are lines of swirl marks inflicted by poor machine polishing attempts. A few of the more common forms of defects are shown in the images below.

Serious swirl marks really stand out on dark coloured paints

Water spotting and swirl marks characterise this neglected paint finish

Serious buffer trails and stone chips are blighting the front end of this BMW

Stone chips and scratches are obvious types of defect whose cause is clear, but what about swirl marks, water spots and etching? What are they and how are they caused? Swirl marks are circular patterns of fine scratches that resemble the form of cobwebs (hence why they are sometimes referred to as cobwebbing). They are nearly always the result of poor washing technique and are virtually guaranteed to be inflicted if you use automatic car washes (those rotating bristles aren't as soft and gentle as they look). The other classic cause of swirl marks are traditional sponges, as they provide no means of lifting particles of dirt safely away from painted surfaces when they are being washed. Instead, particles of dirt and grime are held on the face of the sponge and moved around over the underlying surfaces, creating fine scratches.

A popular misconception is that because swirl marks always appear in circular patterns, they must therefore have been caused by scrubbing the paint in a circular fashion. This is not true. The reason why swirl marks appear to be circular when viewed in the sun, or under any other form of point source lighting for that matter, is that the sharp edges of the fine scratches present in the paint are catching and reflecting light radiated outward in all directions from a single central point. If you look at the same surface under a highly diffuse source of lighting, you will actually discover that the fine scratches are running randomly in all directions; they just appear to be circular when viewed under any form of point source lighting for the reason given above.

Water spots may form on painted surfaces when hard tap water is used to rinse off after washing and is then left to dry off naturally. The spots themselves comprise calcium carbonate, or limescale as it is more commonly known, and other evaporative salts. If such spots are left on painted surfaces for any significant length of time, they can harden to the point where they become very difficult to remove, even by machine. In extreme cases, such deposits can attack underlying surfaces, causing etching. Etching refers to chemical erosion of the uppermost layer of paint (more often than not a clearcoat), and is also caused by the corrosive effects of strong organic acids in bird droppings and bug remains. Such contaminants should always be removed as quickly as possible in order to lower the risk of etching occurring.

Can all sub-surface defects be corrected by polishing? Sadly, the answer is no. Critical to this issue is the depth of the defect in relation to the paint system. Most modern paint systems are made up of three layers; a basecoat of primer, then a layer of flat colour and finally a topcoat of clear lacquer, commonly referred to as the clearcoat. The clearcoat on many modern cars is often twice as thick as the underlying colour layer and is designed to enhance the appearance of the finish as well provide environmental protection. Most sub-surface defects usually only affect the clearcoat and can often be fully corrected by polishing. However, if the defect has penetrated the deeply into the clearcoat or, even worse, exposed the colour layer then polishing will not help; in these cases your only option is a trip to the bodyshop for a partial respray. In our experience, most stone chip damage falls into this latter category. A good test of whether a defect can be corrected by polishing is the fingernail test; if you run your fingernail over a defect and it catches, even slightly, the chances are it is too deep to be corrected by polishing alone.

How can defects be corrected? Defects in the clearcoat can be corrected in one of two ways. Firstly, you can lower the level of the clearcoat in the vicinity of the defect by aggressive polishing until the defect is no longer visible. In general, it is safe to remove up to 25% of the thickness of the clearcoat over the lifetime of the car; anymore and you risk paint system failure. The benefit of this technique is that the defect is permanently removed, but the downside is that such action can compromise the integrity of the clearcoat, particularly if undertaken on a regular basis. The second option is to lessen the severity of the defect by gentle polishing and then try to hide or mask the remainder of it before applying sealant or wax protection. This is undoubtedly a safer option, but the downside is that the correction is only temporary; whatever you use to fill the defect will eventually be eroded, making it visible again.

In addition to the choices given above, you also have the option to work by either hand or machine. Polishing by hand is not a waste of time, although it is fair to say that it is hard work and the results will be limited to some extent. If you have any defects worse than minor swirl marks you will be hard pushed to remove them working by hand; the best you can hope to do is lessen their severity and then consider trying to mask them prior to applying protection. Machine polishing opens up greater possibilities, both good and bad. Whilst it becomes possible to fully correct even quite serious sub-surface paint defects, it equally becomes possible to remove too much of your clearcoat in a short space of time. If you go down the road of machine polishing, do your homework, follow the advice laid out below and in our supplementary guide entitled 'What polish should I use?', and set aside a reasonable amount of time for practice in order to gain experience.

At this stage of our discussion it is also important that we raise the issue of paint hardness as a critical factor in the safe polishing equation. Quite amazingly, paint hardness varies significantly between different makes of car, and also in some cases between different ages of the same make and model of car. The reasons why this is so are quite involved and the implications for choosing an appropriate polish for the task in hand are significant, so for these reasons we have written an additional guide entitled 'What polish should I use?' covering these two topics in detail. However, suffice to say for now that it is extremely important that paint hardness is properly taken into account when polishing because if it is not, then completely inappropriate products may be selected that either remove too much paint or turn out to be completely ineffective.

Now we can start to see why some people are daunted by polishing. Not only can we tackle defects in different ways, but we also have to take into account how the material that we are polishing can vary in terms of its hardness characteristics. If this level of complexity wasn't already bad enough, we now have to add in a third factor; that of product selection. It is no surprise that many car care enthusiasts are confused by the polishing process, for there are literally dozens of different polishes available on the market, all named and marketed in different ways. However, when you look past the choice and the labels, four main categories of polish appear, and these categories are the key to really understanding polishing, as they unify all of the other options outlined above. For this reason, in the next section we will explore these four categories of polish in more detail before then moving on to look at polishing techniques in more detail.