It puts the finishing touch on a paint repair, so do it right. Here are some guidelines.

A buffer/polisher is one of the most effective and versatile tools in the auto body repair shop. In the hands of a professional, it can eliminate myriad flaws in the finish and produce a new car shine that will impress even the most demanding customer.

Basically, the purpose of buffing is twofold: to remove surface imperfections such as runs, sags and dirt particles, and to match the surface texture of the repaired part to the rest of the vehicle. The high-speed buffer smoothes or cuts the new paint surface, enabling the paint technician to better match the original finish.
Before picking up the buffer, inspect the repair area for tiny dirt nibs and level of orange peel as well as more obvious surface flaws.
Then, take film thickness readings on the repair area to make sure there is enough clear coat to polish (See Sidebar, “Using a Mil Thickness Gauge,” on page 53).
This measurement is more critical on horizontal panels than vertical panels because horizontal surfaces are more prone to damage from ultraviolet rays. Generally, car manufacturers require a color thickness of .3 mil to .5 mil, and warranties require at least 1.8 mils of clear coat. Buffing operations should not remove more than .2 mil (.002 in.) from the complete paint system.

Next, protect adjacent parts and areas before buffing so the buffer doesn’t burn into the paint film in those areas and to prevent buffing compound or polish from splattering.

Wear vinyl gloves so you won’t get fingerprints on the surface. Also, some buffing products contain silica, a known carcinogen, so check the Material Safety Data Sheets (MSDS) to make sure you’re wearing the proper respiratory protection. A NIOSH-approved particle respirator, or at least an approved dust mask, is required. Safety glasses are also required.

Ready, Set, Buff
Now you’re ready to begin. Choose a professional variable-speed buffer with a method of changing the maximum speed. Recommended buffing speed is about 1,500 rpm. Make sure you do not exceed 2,000 rpm.

While buffing, try to keep the cord over your shoulder, so it’s not in the way.

It’s important to keep product splatter to a minimum. One method of preventing splatter is to first rub the product with the pad over the area you’re going to buff. Then turn the buffer on and begin. Another method is to turn the buffer on and pull the buffing pad into the product in a counterclockwise direction. Still another method, especially when using a foam pad on a side panel or small area, is to apply the product directly to the pad. Spread the material on the pad or on the vehicle, and don’t start the buffer until it is on the panel.

Buff about two square feet at a time, and work slowly, in a continuous straight-line motion, overlapping the previous strokes about 50 percent. Don’t stop when changing directions. Try to keep the buffer as flat as possible. Lift it only slightly to change directions and where the natural contours of the vehicle require angling the pad to reach most of the surface. Buff “off” the edge of a panel or bodyline, not “into” it.

Once the original defect is eliminated, you’ll need a polish to remove the swirl marks left by the wool pad and compound, and to restore the shine. A foam pad is recommended for applying the polish.

Polish using the same method as when using a buffing compound. Keep the area about shoulder width. When buffing a hood, that means just 1¼4 of the hood at a time.

Don’t let the product dry out on the panel, or too much heat will be generated. When the product flashes and begins to shine, move on to the next area—after cleaning the buffing pad.

When you’ve finished applying one product, remove the excess film with a clean, soft cloth and inspect the surface.
After buffing, it’s a good idea to check the paint film thickness to see how much paint film was removed during sanding and buffing operations. If too much paint film was removed, additional clear coat may have to be applied.

As a final step, some shops apply a wax or finish glaze by hand or machine to surfaces that have fully cured. Some waxes impart a relatively long-lasting protective coat for the finish while others remove dust and fingerprints and make the car look like a million dollars when it leaves the shop and for a few hours after the customer takes it home.

As with any products used in the refinish process, check for recommendations on products and procedures from your paint system manufacturer, or the specific product supplier of the buffing materials and tools used in your facility.

Tips, Techniques, Mistakes
Following are a few tips as well as mistakes to avoid when buffing:

1. To remove lint from a new wool pad, spray it with a mist of water to dampen and then rub it with your hand. Do this two or three times to remove 90 percent of the lint.

2. Use a dry sanding technique rather than wet, because a) dry sanding does not create a slurry, which tends to obscure the work area, making it difficult to see how much orange peel you are removing, and b) you and your clothes will not get damp, which is likely to happen when using a wet-sanding operation. This is no small consideration when you leave the shop and outdoor temperatures are below freezing.

3. If you do wet sand, on the last few strokes go east and west rather than north and south. This will cut grooves into the sanding ridges and create pyramids, which are easier to remove than ridges.

4. When polishing (glazing), apply the polish in a stripe, not in drops.

5. Hold the buffer as flat as possible. The most common mistake is to tip the buffer at too steep an angle. This can lead to deep swirl marks and it puts a smaller percentage of the pad in contact with the surface, making buffing less efficient. It can also cause the pad to “walk,” or to be pulled in a direction other than what you intended, especially on curved surfaces.

6. Avoid going too “dry.” Use enough compound or polish to create a reasonable period of “wet time” behind the buffer as you move it. Applying it too dry can reduce your cut rate by as much as 75 percent. On a 2x2-sq. ft. area, for instance, it should stay wet for about a minute. Then when it dries out you can see if the scratches are gone. Remember that in the buffing operation, material costs are very low compared to labor, so don’t stint on the material.

7. In enhanced polishing, turn the rpms down from, say, 1,800 to 800, and move the buffer in a slower back-and-forth motion. Make final passes in multiple directions, e.g. front to back, then back to front.

Using a Mil Thickness Gauge
An electronic paint thickness gauge can be an invaluable tool for auto body repair shops. For instance, by taking readings on several areas of a vehicle, the estimator can determine if and where the vehicle was repainted. Prior repairs, of course, affect the amount of work necessary to repair the vehicle this time around and the estimate. And at a price of approximately $500, the gauge pays for itself the first time it prevents a redo. Unfortunately, only a small percentage of shops own gauges and an even smaller percentage actually use them.
The gauge is especially useful during buffing and compounding. All the major car manufacturers specify that measurements should be taken before, during and after these steps. The gauge needs to measure to 1¼10 mil because if as little as 3¼10 to 5¼10 of a mil is removed, refinishing may be necessary.

This is primarily because removal of too much clear coat can cause paint failure over time due to the fact that UV absorption is the job of the clear coat. Too little clear and the color coat is not protected from UV radiation. Remember all those OEM peelers several years ago?

For this reason, it’s also recommended that paint technicians measure the clear when buffing since they can’t see how much paint is being removed during the buffing process. Naturally, if the clear coat or color coat is buffed through, the shop will have a redo. But, if too much clear is removed, either on the original OEM finish or the refinished areas, a warranty issue may develop down the road.
It’s interesting to note that painters must now demonstrate proficiency with an electronic paint thickness gauge in order to become certified to perform refinish warranty work for General Motors Corp. (GM) vehicles.