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wet-sanding

THE TWO KEY ELEMENTS ARE THE DEPTH OF THE SCRATCH AND THE COLOR OF THE VEHICLE

I’m sure most of you have heard the term “wet sanding” or “color sanding.” What do these terms mean and when and how should you use these procedures? Sometimes the only way to remove or lighten a heavy imperfection is to sand the paint surface. This can be a fast and effective way to remove a heavy scratch or scuff — if you are skilled and very careful. On the other hand, this method may lead to a trip to the spray booth if you are over-zealous and not aware of when to stop.

During the process of wet sanding, you are actually “shaving” a minute layer of clear coat off the paint surface to level out a deep scratch. This is also the process used to remove scuffs or marks left by other cars. Wet sanding is also used in many body shop procedures, such as evening out a run or sag, eliminating dry spray, “knocking down” too much orange peel, or getting rid of dirt that got caught on the finish during the paint process. In many cases, wet sanding can be more effective than trying to compound these imperfections out. Wet sanding will not create the heat that compounding will but, many times, is more aggressive, and special care must be taken throughout the entire process.

 

CHOOSING YOUR WEAPONS

Sandpaper comes in a variety of grits. Similar to sanding wood, you start with a more aggressive paper and graduate to a finer paper, which will remove deep sand scratches and produce a smooth surface. The lower the number the more aggressive the paper will be.

Grits will range from 400 to 3000. The most popular and common papers to use are 1500 and 2000 grit. For vehicle applications, a grit no more aggressive than 1000 should be used. If you use a more aggressive grade, you must remember not to shave more than .3 to .4 mils off the clear-coat surface or premature failure may result. The UV blockers are in the top .5 mils of clear. If you proceed deeper than that, the clear will have no UV protection from the sun. Also, paper that is too aggressive will actually rub right through the clear and down to the base coat. It is an unmistakable sight when you hit that tragic point of “mining” a panel by sanding too far.

The term “wet sanding” describes the process literally. The panel you are working on, as well as the paper itself, is lubricated with water. Some brands of paper must be presoaked for a specific period of time before they may be used. Other companies make paper that just needs a quick dip in a bucket of water before you may begin. You should have a bucket of water to soak the papers in, adding just a couple of drops of soap for better lubrication. You will also need a sanding block to back the paper, made of some type of foam or soft rubber, to distribute even pressure across the panel. Don’t use your hand or fingers to back the paper because it will create uneven pressure and may lead to sanding through the paint faster. Keep a spray bottle filled with water handy to keep the area wet. You’ll need a clean dry towel to wipe off the area in order to check on your progress.

 

SAND IT OR BUFF IT?

All imperfections in a paint surface are different and different methods will be used to remove or lighten them. Your skill level, knowledge and expertise will determine if the problem can be fixed or improved without refinishing the area. You would not want to sand something that could be removed by the use of clay or light polishing. On the other hand, you would not try to polish out a deep key scratch. Compounding the area may be an option if the scratch is not too deep. Remember that you will be working in the same area with the buffer until the scratch lightens up or is removed. Be careful about the heat and friction you will be creating and the aggressiveness of both the buffing pad and the compound you choose. Sometimes this method will rub through the paint quicker than wet sanding.

 

KEY FACTORS

Mask off any areas that are not to be sanded.

This is what sanding does to the clear coat: it is hazed and discolored - but most of the scratch is gone!

A piece of 2000 - grit paper with a foam rubber backing plate.

Once you become skilled at wet sanding and are confident that you will not rub through the paint, this method can become a money maker and will show customers that your skill and knowledge is superior to that of your competition. Don’t let customers assume that all scratches can be “compounded out.” Explain to them, in appropriate circumstances, that wet sanding, followed by compounding, may be the only option, but that it is a risky process and will be more costly.

The color of the car will often determine how bad a scratch appears, and how well it can be repaired. Clear coat will always look whitish in appearance when it is scratched. The two key elements are: the depth of the scratch; and the color of the vehicle. A scratch on a black car will always look worse than on a white or beige vehicle, because of the background or the base coat. A scratch on black will have to be sanded deeper to remove it totally. Clear coat will also leave a “scar” and it may still be visible if viewed from a certain angle. Never play the hero and assume that you’ll be able to eliminate an imperfection completely. My opinion is that lightening a scratch (rather than removing it) is a better option than rubbing through the paint, or painting a stripe on the car with touch-up paint. Just remember that, if you rub through the paint, you lose, unless the customer was willing to have the panel refinished in the event the sanding process was unsuccessful.

 

THE PROCEDURE

It is always a good idea to soak the sandpaper you will be using even if the manufacturer says it isn’t necessary. While the papers are soaking, mask off any areas that are not to be sanded. This is especially important for areas such as body lines, pinstripes, panel edges, and moldings. You never want to sand more than you have to and risk damage. Wrap the piece of sandpaper around the sanding block and be sure it is free of any dirt or grit. Take a spray bottle filled with water and wet down the area to be sanded. I prefer to sand at a 45- degree angle to the scratch. This method will help you determine if the scratch has been eliminated because you will see the sand scratches at a different angle than the vehicle scratch.

With all the water involved in this process you may lose sight of the scratch and mistakenly think it has been removed. The water will fill the scratch and hide it. You will also notice that the water runoff has a whitish color to it. This is the clear coat being washed away. You may even get a sniff of paint as you are sanding. The key to this procedure is to apply firm but even pressure to the panel and not to stay in one area too long or you will rub through the clear coat. Periodically, wipe the area dry with a clean soft towel and use a blowgun to dry the area completely. At this point, you will see no shine whatsoever to the panel, and hopefully no scratch. If the scratch still shows through the sand scratches, it means the paper you used was not aggressive enough, or the scratch is too deep to be removed completely. This is where you must decide whether to use a more aggressive paper or to finish the procedure and hope for the best.

Even if the scratch is gone or lightened sufficiently, there is still more work to be done. You must follow up with a lighter grade of paper or two to make the buffing process easier. For example, if you started with 1200 grit, follow that with 1500 grit, and then move to 2000 grit. The finer you go with the paper, the easier it is to buff those sand scratches out. You never want to see sand scratches through the clear. This is why I like to finish everything with 2000 paper. It will not take that much more time. At this point don’t lose concentration. If you did not rub through the clear with your 1000 or 1200 paper, don’t assume that you can’t rub through with 1500 or 2000 paper. You may be using lighter grades of paper, but you are still “sanding” the panel.

 

GET THE SHINE BACK

Congratulations! You have sanded out the scratch, but look what has happened to the panel. There is no gloss! The finish is white and chalky looking. Now it is time to buff the sand scratches. There are a number of ways to go as far as pad choice (wool or foam) and compound or polish are concerned. If you have sanded to 2000 grit, the sand scratches are not that difficult to remove but, as stated in previous articles, you must be careful not to create too much heat and burn the paint. Don’t be in too much of a hurry to see the shine come back. It may not appear on your first or second pass, but it will start to return. Work slowly, and gradually proceed to a polishing procedure to remove any swirl marks and bring up a high gloss.

Always ask your customer if he is willing to have the panel refinished.

At this point you should have a nice deep gloss with no swirl marks and no sand scratches showing through the clear. Be aware that remnants of the scratch may still appear if it was very deep. Deep scratches in clear coat leave what looks like a “scar” if they have not been totally eliminated. This is not your fault; it is the nature of a clear-coat surface. Explain to the customer that had you gone any deeper with the sanding process you might have ruined the finish, resulting in the need for refinishing of that panel.

 

RISKY BUSINESS

Wet sanding can be risky if you don’t quite have the grasp of how to do it. Always explain the process to the customer and ask him if he is willing to have the panel refinished if the scratch is not completely removed, or if you rub through the clear. His answer will determine how aggressive you can be. Don’t set yourself up for problems by trying to be a hero.

Ask the local body shop for discarded panels that still have a large area of good paint, and practice, practice, practice! You may never be perfect, but practice will increase your skill and knowledge, and improve your ability to make accurate judgements about future repairs.

 


Kevin Farrell owns and operates Kleen Car, a full-service auto detailing business located in New Milford, NJ. His background includes auto dealership experience and training through DuPont, General Motors and I-CAR.

 

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