Containing Paint Contamination

Containing Paint Contamination

The paint department in today's "high tech" collision repair shop has equipment and materials that offer the potential to turn out some of the finest finishes ever on vehicles. Painters know these systems and have available to them technical assistance in more ways than ever before. With all the technology, high-quality equipment and materials at hand, paint problems still occur. One of the most common, as well as frustrating, problems is that of paint contamination.

Paint contamination is any unwanted foreign particles or substances in the paint film finish that cause an unacceptable appearance. This may include dust and dirt as well as moisture, air bubbles and trapped solvents. These can lead to visible particles in the finish, loss of gloss, fish eyes, micro popping (bunches of tiny solvent pop craters), pimples, or a gritty-looking finish.

First of all, to prevent any of these conditions from occurring, the painter needs to identify the cause. The cause or source can be any one of many or even a combination of things. Here are the major factors involved:

Let's talk about paint product, and specifically, the "misuse" of it. If we deal with a fresh container of paint product, seldom is it contaminated until the seal is broken. The problems occur when the user exposes the product to contamination. This could be something as simple as leaving the cap off and letting oxygen, moisture and other contaminants into the container. In addition, products are designed to be used in a certain manner and when these guidelines are not followed, products can react incorrectly, leaving results that may look like surface contamination.

Keep It Clean
The vehicle must be properly cleaned and prepared to achieve an uncontaminated finish. This leads us back to some of the basics of refinishing. The first step in any of the refinishing procedures is cleaning. This means soap and water washing as well as the use of surface cleaners. We should clean before any sanding or scuffing begins to prevent pushing contaminants into the finish. This is extremely critical with basecoat/clearcoat refinishing in the color blending areas and areas where clear only will be applied. If these areas react to contamination, it is often hard to correct without refinishing. Even hard water spots on the surface, if not removed, can end up reappearing beyond the color blend area as "whitish" spots when clearcoat is applied.

Washing should include more than just the area to be refinished as dirt is often dislodged from wheel well areas, under rocker panels, out of panel seams and jamb areas while spraying. For this reason, high-volume, low-pressure (HVLP) spray guns make sense in that they do not use high pressure to break up the paint. As a result, HVLP guns are less likely to dislodge dirt than conventional guns.

Some of the new surface cleaners on the market today are products that are low in volatile organic compounds (low-VOC) and have an alcohol base. These alcohol-based products not only clean contamination from the surface, but also work to reduce static buildup on the surface. Static can attract airborne contaminants to a surface and wet finishes. To reduce static:

The toughest surface cleaning problems involve surfaces that have been exposed to products used to protect and beautify the interior, tires and trim of a vehicle. Other difficult surfaces are those that have been sealed with lifetime paint sealant systems. Vehicles with these surface conditions should be identified as early as possible in the repair process. They will need extra attention with cleaners designed to remove the sealant and protectant products. Taking this step prevents pushing these products into the finish while sanding and also eliminates spreading the products during blow down operations.

Masking the vehicle can affect how clean the final finish is. Liquid masking products can lock down dust on areas of the vehicle not being refinished, helping to prevent contamination. Masking off panel seams and jamb areas adjacent to the spray area helps prevent overspray, but can also prevent dust from being dislodged while spraying.

Masking materials, such as the paper and plastic car covers, should be considered as possible causes of contamination in the finish. Watch the masking paper to see that it is not gathering overspray in creases or on pulp fibers sticking out of the paper. If so, change masking techniques, and as for the fibers, consider using a better grade of paper. Do not let plastic car covers or paper flop or move during spraying operations. When using plastic cover material, make sure that masking paper is utilized for approximately 12 inches surrounding the paint spray area. If not, basecoat color may dry and dislodge from the plastic while clearcoating.

Maintenance And Preparation
A shop's paint spray area has some of the largest dollar investments in equipment in the entire operation. The most significant piece of equipment being the spray booth itself. In addition to the booth, you have air supply systems for the spray guns, air makeup units for the booth, paint mixing rooms, mixing systems, heat lamps, prep stations and other smaller items. There are two reasons this equipment needs to have a maintenance schedule. One reason is to protect your investment, and the second is to help ensure uncontaminated finishes.

Often a painter will laugh when asked, "Do you know who is in charge of the daily, weekly, monthly, quarterly ... maintenance and check-off of spray booth and related equipment?" What the laugh usually means is that some housekeeping is done, but other items are handled only when they become a problem. These problems commonly equate to paint contamination. But why wait for a problem to botch up a job? A preventive equipment maintenance program can help eliminate certain contamination problems. These responsibilities could be assigned to any employee, but a check-off system should be in place so anyone can see the maintenance records (see Figure 1).

Painter preparation should include the use of a storage area for safety gear to keep the gear clean. In addition to respiratory protection, some type of scalp and hair protection, as well as lint-free painters' suits and gloves, should be available. These items are not new to the industry, however, they need to be used today more than ever due to stricter safety programs and laws. It makes good sense to protect the health of the painter and additionally realize the potential for a cleaner finish. Overall, the painter needs to approach each job with a positive mental attitude to help avoid contamination.

Air Supply
Air supply to the spray gun is an important issue when dealing with the quality of the paint finish. With more HVLP spray guns being used, it's critical that the volume of air be adequate, clean and free of excess moisture. These items are measurable with the use of special gauges. Manufacturers of air filtration systems can place a test unit on the end of the air hose that the spray gun attaches to and test the air for a known time period (typically, for 15 minutes). At the end of the test, they can remove the special filter medium from the unit and see how much moisture and how many particles have moved through with the air. Particles can be viewed under a lighted magnifying glass to determine their makeup. (This can also be done with any contamination in a paint finish.) Changes can be made to the air supply to correct poor conditions. Dryer units can be installed, as well as quality filtration units. These units may remove moisture or foreign particles or could be multistage units capable of doing both.

Paint companies that offer lifetime guarantee programs in partnership with the shop recommend that the air be tested and meets minimum standards before offering such a guarantee. This is done because the film build of high-solid finishes is less forgiving. Trapped moisture in a finish will look similar to solvent pops (also referred to as "micro-pops") or bunches of tiny craters and little pimples, some of which may still have moisture in them. In addition to moisture, lubricants from the compressor or the inside of air lines can make their way to the spray gun. Dirt, carbon, metal particles and foreign materials can also enter the paint job through the air supply. Test the air supply and then determine a plan to correct any problems found.

Correcting Problems
Once a paint job has dirt and other contamination in it, a corrective plan of action needs to be determined. During the spraying process painters use many differing techniques to bury or hide problems that occur. If the contaminant is lint or some other larger particle(s), as is often the case, the painter may use some type of pick tool or tweezers to fish the particles from the wet finish. These areas should than be reflowed with paint product while the film is still wet to prevent a void in the film.

If the problem is not to be corrected until the paint film is dry, one of two choices exist: sanding and buffing techniques or sanding and reapplying finish. Sanding and buffing techniques can be performed by wet sanding or dry sanding. Buffing would then follow using a cutting compound to remove sanding marks followed by a polishing product to remove the cutting compound marks. The use of filler-type product to cover up sanding and buffing marks would not be ideal as these materials will wash away after a short period of time and leave the finish duller due to the fine scratches. All sanding and buffing procedures should be done following the paint manufacturer's recommendations and using a detailing system from start to finish.

When sanding and buffing techniques are used, it's important to know what the paint manufacturer's minimum dry film thickness for the clearcoat is, or the maximum that can be removed from a single-stage color. The use of an electronic film thickness gauge that can read in tenths of a mil or in microns will be needed to obtain these readings. If the film thickness is not monitored, the topcoat can be left without proper protection and the paint will fail after time. Paint manufacturers can supply the guidelines for their products.

The refinishing option is sometimes required if the foreign particles are visible after sanding. It may then be necessary to reapply color to those areas. Reapplying clearcoat rather than buffing may be more desirable as it leaves the finish with a higher gloss and more correct-looking appearance to match that of the original equipment manufacturer (OEM) finish on many vehicles. This also ensures the paint film thickness has not been destroyed.

In this age of "high tech" finishes, we need to remember that causes of paint contamination go back to the basics. Reviewing the basics will help find the causes of contamination, and most importantly, how to prevent contamination from happening.

--The author of this article, Tom Brandt, is an auto body instructor at Winona Technical College in Winona, Minn. He is also an Inter-Industry Conference on Auto Collision Repair (I-CAR) instructor.

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AutoInc. Magazine ®, Vol. XLIV No. 3, March 1996