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Paint detailing techniques: How to approach commonly seen defects

Friday, July 13, 2012 - 05:37
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Shop foremen have been known to say that "if the buffer is running, we're not making any money" (Fig 1). Does that mean all paint detailing is a form of repair, and that all defects should have been prevented? I suppose theoretically that all paint defects can and should be preventable. But in practical application, it is inevitable that defects will occur.

What defects are we talking about? Whole chapters have been written regarding the identification and repair of paint defects. We do not have the time or space to review them all, but will concentrate on some of the more commonly seen defects that can be either prevented or easily repaired.

If we were to narrow it down to just a few of the more commonly seen defects, they would be: runs, orange peel, solvent popping, dirt nibs, fish eye and overspray. Since this list is by no means a comprehensive one, these may not be your most common defects because of your individual shop's conditions. However, these are the more commonly seen defects in many shops, and reviewing them will provide a good idea of how to approach them, as well as others you might encounter.

A few terms and their historical context might be of value at this point. For those painters who have been around for some years, we will recall the days of lacquer paint, when all paint jobs needed to be buffed. A relatively aggressive "rubbing compound" and aggressive wool pad were used on every paint job that was produced. Lacquer paint, when first applied, does not shine at all, and must be buffed to the desirable gloss. A technique used back then was significantly different than the polishing that is done now; and later in this article, we will identify the differences between the aggressive buffing compounds of years past and what is available to us now.

These six common defects are ones that can be prevented either during application (runs, orange peel, and solvent popping) or during surface preparations (overspray, dirt nibs and fish eye).

Runs

Whether you would you call it a run, sag, drip or curtain-run, these names all refer to when, during the paint application, an excessive amount of paint is deposited in a very limited area (Fig. 2). When heavy amounts of paint are applied, the surface tension of the liquid within the paint is unable to hold it flat to the surface of the vehicle, and gravity pulls the excess paint, forming a run.


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Not all runs can be repaired. Some must be sanded flat and repainted, depending on the severity. Others can be sanded with something such as a pumice stone (Fig 3), which comes in different grits; the ones in the photo show 1,500 and 2,000 grit varieties. The flat surface of the pumice stone is held over top of the run and sanded until the surface is flat, using the 1,500 grit. This process is followed by the 2,000 grit and is continued over a slightly larger area. Then the area is polished until the repair is undetectable.

Some technicians are able to use a razor blade held perpendicular to the run, scraping off the excess paint until they reach the surface of the vehicle. Then the surface is lightly sanded and polished, producing an undetectable repair. This process is an excellent and fast way to remove runs, but it does require a great deal of patience and practice. Many, in fact most, who attempt this repair technique end up doing more damage than repair on their first several tries! It may be wise to make a test panel and attempt the razor blade technique on an unimportant panel prior to doing it on an automobile.

Orange peel

Orange peel (Fig. 4) is often caused because of poor gun adjustment as the paint is being applied, although it also can be caused by incorrectly reducing the coating before application. Gun setup and adjustment are critical to a smooth and flat appearance of a coating. If the needle/nozzle combination is not specifically matched to the coating being applied, the air pressure – especially when using an HVLP (high volume low pressure) gun – is not sufficient to atomize the paint properly.


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In this case, the heavy appearance of orange peel will be deposited. Fluid needle adjustment (Fig 5) can help some, but if over-adjusted, the gun will again no longer work properly. When all things are equal, a spray gun operates best at wide-open settings for both the fan adjustment and needle adjustment. Adjustment of the two from time to time is necessary to compensate for environmental conditions.

Proper reduction amount of coatings is also critical when trying to control orange peel. If a coating is mixed at the wrong viscosity and it is too thick (slow viscosity), orange peel is likely. If the coating is mixed too thin (fast viscosity), runs are likely.

Not all orange peel is created equal. As painters, we would like our paint jobs to be perfectly flat and straight, with no signs of orange peel or any other defects. But if we are to apply a coating that results in an undetectable repair, as professional painters we must match the factory orange peel, if it's present. This can be done by slowing down our rate of travel, causing the paint to be applied at a higher film thickness rate, and often producing slight to moderate orange peel. Generally speaking, the orange peel of a factory paint job can be matched using this application technique.

Solvent popping

Solvent popping (Fig. 6) is an application phenomenon that occurs when a second coat is applied without sufficient flash time of the first. Solvent, which is still trying to gas out, is trapped underneath the second coat, and as it migrates to the top it bursts, leaving a small crater.

Solvent popping, dirt, and fish eye are commonly mistaken for one another; but with a little knowledge, they can be easily distinguished from each other. First of all, solvent popping generally has a panel-wide distribution, whereas dirt nibs are often found in a single location, often adjacent to a body gap. Dirt that has not been cleaned out properly comes out during application. Fish eye also is limited to a small area, and when examined closely (Fig 7) shows a larger crater, almost volcano-like, where the oil contamination has gathered.

Solvent popping may not be repairable and if severe, the surface must be sanded and repainted. If the solvent popping is not severe, though, the surface may be repaired by sanding and then polishing to produce the desirable gloss and undetectable repair.

Dirt nibs

Dirt nibs (Fig. 8) are a defect that can be attributed directly to the vehicle not being cleaned properly during preparation. When cleaning a vehicle for paint, there are two phases that must be attended to closely. First is soap and water wash. The majority of vehicle contamination is deposited on the vehicle either during normal operation, or while in the repair process. Dirt is a water-soluble contaminant, and the majority of cleaning is accomplished by a good washing with an automotive soap (PH balanced) and water (Fig. 9).


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Following that, a chemical cleaning with a wax and grease remover will take care of contaminants that were not removed by the soap and water wash. The use of a tack cloth just prior to the application of a coating is also critical to removing the small dust particles prior to painting.

Most dirt contaminants can be lightly sanded or even spot sanded (nibbed), and then polished as needed.

Fish eye

Fish eye (Fig. 10) is caused by a contaminant on the surface prior to application of paint. Generally speaking, that contaminant is a light oil (silicon), which has, by whatever means, found its way to the surface of the vehicle. When paint is applied on top of this contaminant, the paint is unable to adhere to the oily surface and a "fish eye crater" is caused.


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Fish eye is a preparation defect. If the surface has been properly cleaned and degreased using a wax and grease remover, fish eye can usually be prevented completely. If fish eye does occur, particularly in the first coat, often painters will let that coat fully tack off, then follow it by a second coat, which often "bridges" the fish eye so that it becomes invisible. A third coat is applied, not only for full coverage but also to make sure that there is sufficient paint for detailing later. After the paint is fully cured, if slight remnants of the fish eye are visible, it can be sanded and polished.

If during the second coat the fish eyes are not bridged, it is highly unlikely that a third coat will accomplish an acceptable result. Therefore, in this instance the finish should be dried, sanded and repainted.

Overspray

Overspray (Fig 11) is an application and preparation defect. If overspray is noted on glass or panels, which were covered with masking, the defect occurred because overspray was able to migrate underneath the masking. Proper masking, applied tight to the surface and with no gaps, is critical not only when spraying but also during detailing the vehicle. Leave as much masking paper on the vehicle as possible when sanding and polishing. This allows the vehicle to be cleaned more easily after polishing (Fig 12).

The removal of overspray, especially from glass, moldings, and other areas that are not freshly painted, is often easily accomplished by using detail clay (Fig 13). Although detail clay looks like children's modeling clay, it is a specially formulated substance that clings to the overspray, removing it from the surface. Detail clay must be used with a spray lubricant, often offered by the same company that produces the clay.


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The procedure involves first making a solution of light soapy water, such as is used for wet sanding. You knead the clay in your hand until the surface appears clean; then you can flatten the clay. After the car surface is moistened with the lubricant, the clay is rubbed over the area to be cleaned, thus lifting the dirt contaminants.

No matter what type or degree of detailing is needed, there are some points and procedures the detailer should understand and keep in mind to achieve the best results.

Least aggressive first

One of the most important theories to understand when detailing an automobile is to use the least aggressive method first. It is easier to go to a more aggressive process (because no damage has been done by using a less aggressive method) than it is to repair the damage done by starting with the too-aggressive method. Modern detailing products can range from very aggressive sand papers (P600 or P800) down to very mildly aggressive products such as P2000 or higher.

Polishing compounds also come in different aggressive grits, and even some polishing bonnets are more aggressive than others. Wool or a wool combination bonnet (Fig 14) is much more aggressive than a foam pad (Fig 15) with a waffle surface, which can easily glide over the surface of the area to be polished, causing little or no damage.

Since starting the detailing procedure at the right level is so necessary, inspecting a vehicle and coming up with a polishing plan is critical.

Inspection

If a vehicle is noted to have a paint defect that must be detailed, closely examine the area with a magnifying glass, such as a 10x magnifying glass with an attached light often sold to help older persons with their reading. This instrument is very helpful in identifying the type of defect requiring repair.

Remember, often dirt nibs, solvent popping and fish eye can look very similar. Without a close inspection, the technician might attempt to start the repair process using an overly aggressive approach, which will likely cause more damage than good.

By thoroughly inspecting the surface of a vehicle to be repaired, you can make a plan of attack to repair any of the above defects, or others that may exist. If it is determined that the defect cannot be repaired, the surface must be prepared for each coating. But often the repair can be detailed away.

Cleaning

Cleaning prior to detailing is almost as important as cleaning prior to painting the vehicle. Contaminants can easily find a way to the surface of a freshly painted car, even one that was sitting undisturbed in a shop for only a few hours. These contaminants can be more aggressive than the P2000 grit sandpaper that may be used in preparation for polishing.

The more masking paper that can be left on a vehicle during the detailing process, the easier the cleanup process after detailing will be. Therefore, care should be taken when cleaning a vehicle prior to detailing so as not to overly wet the masking paper. Often a spray bottle with soap and water and a microfiber cloth (Fig 16) are used to remove any contaminants.

Sanding, scuffing or nibbing are all processes used to remove contaminants prior to polishing. Care should be taken when sanding to use a block of some sort (Fig 17) to prevent finger marks (Fig 18) during the sanding process. Often painter DAs, which have a small less-aggressive orbital pattern (Fig 19), can be used by the aid of an interface pad (Fig 20), which allows a DA to be used when sanding a vehicle prior to polishing.


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If you are unsure as to the orbital pattern of your DA, any pencil can be held lightly against the surface of the sandpaper as the DA is turned on. The resulting pattern will indicate the size of the stroke (Fig 21).


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Buffing polishing

The term buffing usually refers to a very aggressive process, and is no longer the commonly chosen practice for detail repair. Polishing, on the other hand, now can be done at multiple levels of aggression. A technician can choose something relatively aggressive both to polish and to speed up the job; or a lighter polishing can be used to take care of some of the less demanding repairs.

The speed at which the polisher runs is critical. Many companies recommend 600 to 800 RPM. This allows the surface to remain cool as it is being polished. The waffling in the pads is also designed to keep the surface cool while polishing. If the surface becomes hot from too aggressive a speed, bonnet or compound, the paint can be quickly polished away, and a "burn through" which is often not repairable, is the result.

Polishing machines, whether air-driven or electric, should be held as flat to the surface as possible (Fig 1). This allows the greatest surface contact with the pad, and thus speeds up the polishing process. Often following sanding, mica or fine scratches remain in the surface, and technicians sometimes are frustrated with the amount of time that it takes to polish correctly. By using the least aggressive first methods when repairing defects, the polishing time can be minimized.

Detailing

This process prepares the vehicle for delivery to the customer. The masking is removed and the vehicle is washed, especially inside door jams (Fig 22), where polishing compound migrates and is often messed. All glass is washed thoroughly. The repair order is checked; and all doors, windows, and other vehicle operations are checked prior to delivery to the customer.

Final detailing is often thought of as the final quality control step in a collision repair business. It may be performed by an entry-level employee and checked by a shop foreman prior to delivery. But no matter who does it, detailing remains one of the more critical aspects of the repair process.

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