Today's paint techs need to know more than just how to spray paint to perform a quality repair
There was a time when the only spray techniques a painter needed to perfect were the actual techniques of spraying, such as distance, overlap and travel speed. These basic techniques are still critical to good paintwork, but now a painter must also be concerned with a whole gamut of techniques that make the refinish/ repair undetectable and profitable.
A productive painter in today's market must be proficient at techniques that return a vehicle to its pre-collision condition. To do this successfully, the repair must be undetectable; the finish must match the vehicle's color, metallic orientation and texture; and the repair must be completed in as short a cycle time as possible, while keeping the material usage as low as possible. In addition, the technician must do all this while complying with national, state and local environmental and safety laws.Painters, to be proficient, must master not only the physical techniques of applying paint, but also the sometimes more difficult tasks of time and material management. In larger production shops, a lead painter must also develop leadership techniques, which will enable the department to work as a team. Therefore, a painter's day is filled with decisions that become critical to the overall process of restoring a vehicle to its pre-collision condition.
Today's paint technicians must regularly make several technique decisions confidently to assure a successful repair/refinish. Is the test panel a blendable match or does the color need to be tinted? Which blending technique (standard forward blending, reverse blending or wet bedding) is best for a particular color? Which clearcoat is best for the job, and which clearcoating technique should be used? Should the vehicle parts be painted on-or off-vehicle? Should the repair be performed with UV products (UV primer and clearcoat)? How can the painter complete the refinish with the highest transfer efficiency?
First, let us look at the technique of a test panel. Though test panels have been around for years, not all painters choose to use them. Some painters will instead mix the formula, stir it and then hold the stick up close to the vehicle and "eyeball" the color. However, this method of color testing actually tells the painter very little about whether the paint will match or not. To get accurate knowledge that a color will match, the technician must spray a test panel.
The commercially available test panels have black and white checks that eventually become covered so the painter can tell how many coats of basecoat are needed to achieve full coverage (Fig 1). They also have space on the back for the painter to note the color formula or its variant that was selected, how many coats of basecoat were needed and which clear was used. For a test panel, the paint should be mixed and reduced according to the paint manufacturer's recommendations and should be sprayed using the same paint techniques that will be used when the vehicle is painted.
After it has been sprayed, the test panel is compared to the vehicle using sunlight or a sun-corrected light to determine if the color is a blendable match. The metallic orientation also can be observed at this point to determine which blending method is best for this vehicle and its color. The test panel can be kept with the customer's records or the painter can keep it in his or her personal file for future reference.
With the test panel complete, the painter must next decide which blending method should be used. The standard and most often used blending method entails the first coat of paint being applied to just beyond the repaired area, the second applied beyond the first, and the subsequent coats being progressively larger (Fig 2). The number of coats needed to reach hiding is determined by the test panel; though three coats may often be sufficient to cover, more may sometimes be needed. If the test panel reveals that more than three coats are needed, the progression should likewise be adjusted. This technique is best-suited for simple blending of coatings that do not contain large amounts of metallic or mica.One of the limitations of this common method of blending, though, is that each new coat of paint is applied over dry substrate. Thus highly metallic paints may not lie correctly, and that imperfection may be noticed in the finished product.
The reverse blending technique is used if the paint is a difficult color to match or when metallic orientation is predominant. Using this method, the painter applies the first coat at the farthest point first, with the second coat being applied in from that one, and the subsequent coats being progressively smaller (Fig 3). The last coat should cover at least the size of the repair to assure hiding. Because each subsequent coat is applied over the previous wet coat, the newly applied paint will allow the metallic to lie with more ease.Many painters now use reverse blending as their routine blending method. Though this type of blending will be sufficient for most colors, there are some very highly metallic colors, such as silver and bronze, in which the paint formula consists mostly of metallic with little pigment. These colors may require a blending method that will allow the metallic to land in a wet substrate from the first coat on, to help orientate the metallic lie on the surface. This method has been called "wet-bedding."
The surface of the part to be wet-bedded is prepared in the same manner as the blending methods outlined above. The difference is that a blending clear is applied to the complete panel before the first coat of paint is applied. Following the recommended flash time, the painter employs the reverse method of blending, with all the metallic landing on a previously coated area, thus helping with the lie of the metallic (Fig 4).Most paint manufacturers provide blending clear. Some call it adhesion promoter, but most will provide a clear that is compatible with their basecoat system and that also can be topcoated with clear.
Next it is time to choose the proper clear and the proper clearcoating application technique for the vehicle and its color. Painters today have a staggering array of clears to choose from. Some can be force-cured in very short times, such as eight minutes or less; but because these clears cure so rapidly, they are not suitable for clearing more than three panels at a time, or difficulties may arise. Some shops choose to limit the clear choices to only two, such as a hyper cure for small jobs and a clear that can be sprayed on vehicles with multiple panels to be covered, thus requiring a slower curing clear.
Once the clear has been chosen, the next step is to choose the clear application procedure. Most painters, when reading the manufacturer's recommendations for number of coats of application, will find that two to three coats are recommended, and will apply two coats. Then, if they see any defects that will require sanding and polishing, they may choose to apply the third coat so "they will have something to sand."
However, if they carefully read the recommendation, technicians will also find that the newly applied basecoat needs to have 2 mils of clearcoat remaining after detailing. When most paints are applied according to paint manufacturers' recommendations, they will have about 1.5 mils of covering per coat, with two coats having a total of 3 mils when applied. This leaves approximately 1 mil of clear that can be sanded and polished. Since even aggressive techniques don't take off this much film thickness, the third coat is seldom needed.
According to studies at the University of Northern Iowa Spray Training and Research (STAR) Program, among the painters whose spray techniques have been tested, most exceed the recommended film thickness by 100 percent. Thus spraying two coats of clear could result in a film thickness of as much as 6 mils, meaning that applying three coats is never needed to meet the paintmakers' recommendations.
When the technician is applying clear, even two full coats over the entire panel may not be necessary. The first coat should be applied to just beyond the basecoat, and the second coat applied over the entire panel. This coverage will provide the minimum of 2 mils needed over the fresh paint (Fig 5). This method reduces the amount of time and material necessary to comply with a paint manufacturer's recommendations.Another paint technique being used to speed up production time is "off-car painting." This technique means the new parts are placed in the booth and are painted completely, not just edged in. The areas on the vehicle that need to be blended are also painted. Then the vehicle is assembled, detailed (if needed) and returned to the customer in a much shorter time than by the traditional method of edging in the parts, assembling the vehicle and then completing the painting.
By using the off-vehicle painting technique, a technician only needs to mix and spray paint once, and the masking can be done more efficiently and faster, thus shortening the vehicle cycle time. While not every repair lends itself to off-vehicle painting, a majority of them do. This method should not be overlooked merely because it means that new processes will need to be adopted and painters may need some training to perform them.One concern with this type of painting is that a part being painted off the vehicle must be held in the same orientation as it would be when placed back on the vehicle. This allows the metallic lie to be properly oriented. If a part such as a ground effect or door cladding is painted while hanging vertically in the booth, then placed back on the vehicle in a horizontal position, it may not properly match the vehicle due to metallic lie. However, stands are now available to help properly hold parts for painting, solving the metallic lie problem.
The next technique that today's painter must master is the use of Ultra Violet (UV) curing coatings. The advantage of this type of cure is the speed at which the coating can reach complete curing. (A completely cured coating means it is cured to the point that it can be sanded, polished, and returned to the customer.) With primers and clears now available that are cured in two minutes when exposed to portable UVA lights, it is easy to see that using them can dramatically speed up cycle time. UV primers available to the collision market today come as clear products. They need to be clear so the UV light can penetrate to the base of this high-build primer. Following the two-minute exposure to the light, the primer can be sanded and the basecoat applied.The UV primer that is not exposed to the light will not cure; therefore, it has an unlimited pot life and can be left in the gun for the next job. This too reduces the time needed to mix primer for each job and the expense of over-mixing, and thus wasting, materials. When the cured primer has been sanded and prepared, the appropriate basecoat can be applied. At this time, colored basecoats are not yet available in UV curing coatings, so a water-based or solvent-based color must be applied. Then a UV clear curing coat can be applied, cured with a light in two minutes, polished as needed, and returned to the customer. The UV clears are also more scratch-and mar-resistant, lending themselves to off-vehicle painting. Additionally, these clears do not have a pot life if not exposed to UV light, and thus a full gun of clear can be prepared at the beginning of the work day and added to when needed for each subsequent job, further reducing the mixing and cleanup time.
Though we do not have a basecoat color available in UV curing at this time, paint manufacturers are working on it and without a doubt this problem will soon be overcome. Because UV curing products have virtually no Volatile Organic Compounds (VOCs), their use reduces environmental impact and will reduce costs that are normally incurred because of the use of VOC-laden products. As it is now, small repairs can be very quickly completed with UV repair systems, and painters are wise to add UV curing to their arsenal of paint techniques.
As the collision refinish industry continues to change, painters who wish to stay on the cutting edge of the industry must continue to learn new techniques. Each of these new techniques has a learning curve; technicians must practice until they are proficient at them. Then the techniques should be incorporated into the shop's standard operation procedures (SOPs). Test panels will assure the paint that is mixed will be the proper color for the job at hand, thus reducing repairs later.
Knowing different types of blending techniques for difficult colors before a technique is tried will reduce time and material costs. Applying the proper amount of clear will also reduce material cost. Painting parts off-car will speed up cycle time and using UV curing materials will speed up production and decrease environmental load and cost.
Painting is an ever-changing profession with paint products evolving rapidly and environmental laws becoming stricter each year. Paint departments' cycle times are always an issue, along with maintaining a high standard of quality. Therefore, painters must explor and master new techniques. Painting is truly a profession of lifelong learning.
