Perfecting Paint Finishes
Wet-sanding and other techniques can rejuvenate a vehicle's surface

By Prentice St. Clair

Before

After

Detailing can be described as the systematic rejuvenation and protection of the various surfaces of the vehicle. Perhaps the most important of these surfaces is the exterior paint, which is the most visible and largest surface to be cleaned and protected.

It is certainly easy enough to wash and wax a vehicle, which takes care of the "protection" part of the equation. But what about rejuvenating the paint surface? The dictionary definition of rejuvenation is "to restore to youthful appearance," which is certainly what we are trying to do with automotive detailing--make cars look new (i.e. "young") again. Rejuvenation can be thought of as a fancy name for cleaning but, in actuality, there are many more options than just cleaning the paint on a vehicle. Think of it this way: Cleaning the paint is much more involved than, say, cleaning the carpets.

In this article, I will discuss some common paint problems and some ways to fix them. Be aware that the aggressive techniques described herein should only be used if there is enough paint to work with on the vehicle. Test an inconspicuous area and, at the first sign of "breakthrough" to the primer, stop work and consider a less-aggressive technique.

The types of paint damage

There are several types of automotive paint damage that can be corrected. They fall into two categories: surface contamination and sub-surface damage.

Surface contamination includes anything lying on top of the paint finish, such as paint overspray, scuffs, drips, ferrous oxide deposits (i.e. rail dust) and other environmental fallout. Usually these types of contamination can be removed using detailer's clay. (However, heavy ferrous oxide or fallout deposits may require the use of acid washing techniques, followed by an application of detailer's clay.) In my opinion, every vehicle that is to be waxed or sealed should be "clayed" first. Every vehicle collects some kind of environmental fallout over time, sometimes enough to be noticeable within weeks of the last clay application. When you think about it, it seems silly to apply wax over this contamination without first removing it. Detailer's clay gives us a tool to quickly and effectively remove such contamination so that the wax or sealant rests directly on the paint surface.

Sub-surface damage includes etching, scratches and oxidation. The main difference between surface and sub-surface damage is that to completely remove sub-surface damage, the paint must be removed down to the bottom of the damage. With the advent of detailer's clay, surface contamination can be removed completely without removing any paint. Other options to remove the appearance of sub-surface damage include "mellowing" techniques that reduce the appearance of the damage and cosmetic or filling techniques that temporarily hide the damage.

Of course, sometimes the damage is so deep that there is no paint left to rejuvenate. In this situation, we turn to paint touchup and spot-blending techniques in which we are adding new paint to the vehicle surface instead of correcting the existing paint.

Correcting sub-surface paint damage

Sub-surface paint damage can be corrected by hiding, mellowing or removing the damage. Hiding the damage is done by applying glaze-laden chemicals to the paint surface. These chemicals fill in minor imperfections in the paint surface, yielding a more solid surface that is shinier and glossier. Keep in mind that the glazing effect has strong limitations: It will only work well on minor imperfections and will last only a few weeks. Typically, glaze is used in body shops after final finishing of repainted surfaces and on show cars that never see the light of day and thus do not require application of protective products such as wax and sealant.

Mellowing techniques involve the use of light polishes and non-aggressive polishing pads that smooth out most but not all moderate paint damage. Use these techniques on vehicles that are detailed often so as to not remove too much paint.

Mellowing techniques can also be used to reduce the appearance of major damage that would otherwise require the removal of too much of the paint to be safe. This is especially true in the case of deeper scratches. The only way to completely remove a scratch is to cut the paint down to the depth of the scratch. But if it is too deep, so much paint will have to be removed that the remaining paint will be subject to premature deterioration. For the customer who does not want the area to be repainted, we can offer the "mellowing" option, which will help to reduce the appearance of the scratch by rounding off the edges using wet-sanding, compounds and aggressive buffing pads. In this case, we are removing only some of the paint, perhaps halfway down instead of all the way down to the bottom of the scratch.

Removing the damage involves removing the paint all the way to the bottom of the damage. This is the only way to make the damage "disappear" completely. I suggest using the following rule to guide your choice of chemicals and equipment: "Use the least aggressive method that effectively removes the damage." We are not going to pick up 1500 grit sandpaper or a wool buffing pad for every vehicle that comes in. We will only use the strongest technique necessary to remove the damage in a reasonable amount of time. Test a section of the hood by starting with light techniques and slowly adding aggressiveness (of chemical and pad) until the damage disappears quickly.

There are two reasons for this approach. The first is obvious. The more aggressive the technique used on the paint, the more paint is removed. Let's try to keep as much of the original paint on the vehicle as possible. The second reason is less obvious. The more aggressive step you start with, the more finishing steps you will have to do to restore the shine of the original paint. Let me explain. When removing paint damage, we use chemical abrasives and cutting pads that leave behind their own super-fine scratches. To illustrate this, think about sanding a rough-cut block of wood with 40-grit sandpaper. The sandpaper will remove the major imperfections in the wood, but the scratches left behind are still fairly obvious and would certainly show through a varnish or paint coating on the wood. Thus, the furniture craftsman will follow the rough sanding with several progressively lighter grits of sandpaper--perhaps 80, 120, 220--before coating the wood with protection (varnish or paint). The same is true if you start with a wool cutting pad and compound. This combination will remove major imperfections in the paint but will leave behind thousands of super-fine scratches that leave the paint surface relatively dull. Thus we follow heavy compounding with several progressively lighter steps of polishing.

Some examples

Let's talk about some common paint damage situations and how to approach them. If the damage is light--in the case of normal washing micro-scratches or minor oxidation over the entire vehicle surface--a random-orbit polisher and some light polish may be all that is needed to remove the damage. If this is insufficient, you may need to move up to the cutting ability of a high-speed polisher and a light cutting or finishing pad.

Moderate damage might include moderate oxidation and scratches from placing objects on the trunk, roof or hood of the vehicle. To remove these might require a heavier polish and a high-speed polisher using a moderate foam cutting pad.

Heavier damage includes etching, heavy oxidation and deep scratches. If a foam pad and compound does not effectively remove the damage, it's time to use our most aggressive techniques, like compounding with a wool pad. If this is not enough or is taking too long, it's time to move it up a notch to wet-sanding.

Wet-sanding

Wet-sanding involves the use of micro-fine sandpapers, ranging in grit from 1000 to 3000, and water as a lubricant. Some people refer to this as "color sanding" because the wet sanding always produced the color of the paint in the run-off in the years when single-stage paint systems were the only kind used. Today, most vehicles are painted using a clearcoat that yields a milky run-off when wet-sanded. Wet-sanding is typically reserved for removing the most severe damage or that which must be removed quickly.

Most major damage can be removed using 1500 grit sandpaper. Use lighter grits to be more careful and more aggressive grits for quicker action. If you use a more-aggressive grit (e.g., 1000 or 1200), it will be necessary to follow with a lighter grit (e.g., 1500 to 2500). But usually 1500 grit sand scratches can be removed using a true-cut clearcoat-safe compound and a high-speed polisher set at low revolutions per minute with a wool pad.

Always wet-sand using a soft foam backing block available just for this purpose. Using your fingers alone can cause "finger channels" in your sanding area. The foam block yields a much more evenly sanded surface. Hard blocks are also available but are usually reserved for removing paint defects such as runs and sags on flat surfaces.

You can use a spray bottle filled with clean water to soak the area and the sandpaper. Use a back-and-forth motion with very light pressure. Sand in the same direction over the entire area to be sanded. This allows you to monitor removal of the sanding scratches during later polishing steps. If you are removing linear damage such as scratches, sand across the damage. As you work an area, continue to spray water to help lubricate the sanding and take away sanding debris that can cause unnecessary scratching.

Work slowly and check your work often. The best way to monitor your progress in removing the damage is to dry the area completely using an air compressor. Once the area is dry, you will be able to instantly see evidence of uneven sanding and whether or not the damage has been completely removed.

A common use of wet-sanding is to remove unsightly "orange peel" from factory-painted vehicles or to match the orange peel of repainted areas with that of neighboring panels with original factory paint surface. Typically, 1500 grit sandpaper is sufficient for this purpose. Follow the instructions above, monitoring your work as you progress. Remove the 1500 grit sanding scratches with a wool pad and compound. Then polish as necessary with progressively lighter polishes and foam pads to bring back the shine and deep gloss of the sanded area. Wet-sanding can also be used to "mellow" extremely deep scratches. Lightly sand, compound and polish the area using the techniques described above, but DO NOT sand all the way to the bottom of the scratch. What you will find is that even a partial removal of the scratch makes it look a lot better than just leaving the scratch alone.

Spot corrections

Often, newer vehicles are in pretty good shape and just have a few rough spots. In these cases, it is not necessary to use aggressive techniques on the entire vehicle surface, just the spots that need it. For example, maybe the trunk has one small area with "corrugated scratches" from the one time that the customer slid a box on the dusty surface. Or maybe there are a few small scuffs on the door panels resulting from impact from the opening doors of neighboring vehicles. This is a common find in households with a two-car garage in which both vehicles are parked.

For these spot-polishing situations, you can use a "spot polishing pad kit" that comes with a backing plate that goes into a standard power drill chuck. These kits have small versions of the pads available for high-speed polishers, turning the drill into a sort-of "mini high-speed polisher." This allows you to direct your damage-removal techniques in a three-inch diameter area. You can even wet-sand the small area first if necessary and then spot-polish out the wet-sanding scratches.

Spot-polishing is a quick and easy way to please customers with newer vehicles that only have a few little areas of heavier paint damage. Spot-polishing is great to use on vehicles that are just getting a simple wash and wax.

In summary, detailing vehicle exteriors involves both rejuvenating and protecting the paint surface. Depending on the damage, there are a lot of techniques that can be used to restore damaged paint. With the proper testing and care, you can go far to achieving a near-new paint surface, while yielding increased profit. Spot-polishing can be included in your higher-priced packages or it can be priced as an add-on to standard service. Extensive paint rejuvenation should be priced accordingly. On average, you will find that each extra step applied to the entire vehicle surface requires about one extra labor hour to complete. In the extreme, wet-sanding and high-speed polishing of the entire vehicle is a time-consuming process and commands a price of several hundred to a few thousand dollars per vehicle. Paint perfecting is a skill that takes time and proper education to develop and should be priced accordingly.

Prentice St. Clair is a San Diego-based consultant to the automotive reconditioning industry. He can be e-mailed at pstc875437@aol.com.

Share this article: Email, Slashdot, Digg, Del.icio.us, Yahoo!MyWeb, Windows Live Favorites, Furl
Add this article feed to: RSS, My Yahoo, Newsgator, Bloglines

Read Comments [0]