Taking a shine to paintwork

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Before spraying, follow the paint manufacturer’s recommended settings for air pressure to the gun, and air and paint volume settings at the gun.

Illustration 1. A painted finish is a sandwich, consisting of: the substrate, or body; OEM or “wash” primer; sanding or non-sanding primer; and finish coat(s). Illustrations 1 through 7, DuPont.

Illustration 2. Cracking, which often extends to primer or substrate, commonly is caused by excessive topcoat thickness, which magnifies normal thermal expansion and contraction, until topcoat splits.

Illustration 3. Featheredge splitting usually is caused by excessive primer. Solvents in the primer haven’t set up, and try to escape.

Illustration 4. Fish eyes are depressions in paint film caused by repulsion of wet paint by contaminants like wax, grease, oil, etc.

Illustration 5. Orange peeling is the inability of wet paint film to level out after application, usually caused by improper gun adjustment or spraying technique.

Illustration 6. Pinholing results from rapid solvent loss or moisture trapped below the paint surface.

Illustration 7. Running or sagging usually results from overgenerous paint application, but solvent that’s too slow for conditions, or too much reducer, also can be culprits.

Nobody expects a fleet manager to grab some sandpaper and a spray gun and refinish a truck, but understanding what goes into a high-quality refinishing job can help you determine whether you’re getting your money’s worth. A working knowledge of recommended refinishing procedures and some of the common refinishing mistakes should paint the picture.

Scratching beneath the surface
A painted finish is basically a sandwich (see Illustration 1), consisting of: the substrate, or body, which can be steel, aluminum, fiberglass, sheet-molded compound (SMC) or flexible plastic; the OEM or “wash” primer; sanding or non-sanding primer; and the finish coat, which often is topped with an additional, clear coat. This is called a base-coat/clear-coat job, which can provide additional depth and gloss.

The most important thing to remember about painting a vehicle is that “a paint job is only as good as what’s underneath,” according to Jerry Parnes, owner of Manayunk, Pa.-based Modern Day Auto Body, which does consumer as well as commercial-vehicle work. “Whenever I’m asked for an estimate, I first ask why the vehicle needs to be repainted,” he says. “If it’s because the original paint is chipped or peeling, there’s a lot more (sanding) work involved.” That’s necessary because any imperfections underneath will show through the finished product, and the base needs to be smooth for the new paint to adhere properly.

Before any sanding, clean the surfaces with soap and water, and dry thoroughly, advises Steve Podlas, manager of OEM & national accounts for PPG Industries. “Otherwise, contaminants on the surface will be ground in during sanding, leaving scratches,” he says. “Also, use a wax/ grease remover to remove tar and similar contaminants.”

After surface imperfections in the original finish are removed, the entire surface of the vehicle typically is sanded with a sandpaper that’s fairly fine – 220 to 400-grit, for example. “Those fine scratches are necessary for the new primer and paint to grab on to,” says Parnes. Using sandpaper that’s too coarse will leave sanding lines that will be visible through the finish coat.

After sanding, “Re-clean to remove sanding dust, and use grease remover again,” says Podlas. “Then, after using a tack cloth, you’re ready to prime.” A tack cloth is treated with a light paraffin to collect surface dust and debris.

Parnes recommends then using a urethane primer to seal the old finish, preventing bleed-through to the new paint. “We use a high-building, two-part primer,” says Cotton Wilson, lead body and paint technician for Southeastern Freight Lines. “It saves time, because it fills in minor imperfections. We do some dry sanding with a 320-grit paper, use a cleaning solvent, blow air over the surface, use the solvent again, then go over the finish with a tack cloth.”

Keeping the surface to be painted free of contaminants is critical to achieving a high-quality finish. “There’s no such thing as a perfect paint room,” says Wilson, “But we try to keep everything as clean as possible.”

Laying it on
If the primer is the non-sanding type, you can go right to the tack cloth, and then start applying the paint. “The most popular choice for commercial vehicles is a one-step fleet enamel, either urethane or acrylic with a hardener,” says Parnes. “It’s a one-step process, it looks good, and it holds up well.”

When mixing paint components – which include the paint, a reducer or solvent, hardener and sometimes an accelerator – follow the directions, advises Parnes. “Paint manufacturers have invested millions in the technology that goes into their products. They know what works.”

Remember, when mixing paint, you’re making a soup, and the recipe has to be just right for the environment in which you’ll be working. Ambient temperature, for example, is critical, and you need the proper viscosity for the day. Again, use manufacturers’ guidelines. If the viscosity is too thick, the surface will look like an orange peel. Too thin, and the paint is likely to run. “Either way, it can ruin your day,” quips Parnes. “Although, given the choice, orange peeling is easier to sand out.”

Once the paint is mixed properly, the spray gun and air system need to be set for the product being used. Again, follow the paint manufacturer’s recommendations, including settings for air pressure to the gun, and air and paint volume settings at the gun. “That’s important,” says Podlas. “For example, if there’s too little air, you’ll get poor paint atomization, which results in a non-uniform appearance.” The gun should produce a wide, even spray pattern that covers completely without running. To check the pattern and adjust your spraying technique, “It’s often best to practice spraying on an old fender,” says Parnes.

Depending on the product, two or three coats of paint, with recommended drying or “flash” time in between, usually will do the job. “For our black panels, we use three coats of DuPont Imron 1000,” says Wilson. “But for the red panels, we use Imron 2000, which is a high-solid paint. Two coats does it, with 10 minutes in between.”

Obviously, it’s important to take the recommended time between coats to let the chemicals work and the paint set up. “I’ve seen more jobs ruined by painters rushing, trying to get out the door by 5 o’clock,” says Parnes. “You can’t do that and expect good results. The chemicals in paint have no regard for your agenda.”

When the job’s done, it’s best to let the paint set up for at least a couple of hours, if air-dried. If you’re going to add graphics, “You’ll want to let the vehicle sit overnight, or even a couple of days before applying them,” Podlas advises.

“At 70 degrees Fahrenheit, a finish takes about 16 hours to cure,” adds James Svaasand, general manager of business ventures, Penske Truck Leasing. “Every additional 15 degrees Fahrenheit cuts the time in half.”

Good work gone bad
Even with the best intentions, painters sometimes make mistakes. Here are some of the most common ones:

The finish in Illustration 2 displays cracking, which often extends down to the primer or substrate. This commonly is caused by excessive topcoat thickness, which magnifies normal thermal expansion and contraction, until the topcoat splits and the crack progresses downward. However, inadequate paint mixing, insufficient drying time, incorrect additives or a surface that’s too hot or cold for the paint used also can cause it.

Illustration 3 shows featheredge splitting, which usually is caused by excessive primer in heavy, wet coats. In that case, solvents in the primer haven’t set up, and try to escape. Take your time!

This problem also can be caused by inadequate mixing, using the wrong reducer, improper surface cleaning or trying to force-dry the topcoat by fanning with air, resulting in the topcoat drying before solvent is released from the primer.

Much dreaded fish eyes are shown in Illustration 4. They’re depressions in the paint film caused by repulsion of wet paint by contamination from wax, grease, oil, handprints, silicone-based sprays and the like. These types of contaminants can come from practically anywhere. “At the last place I worked, technicians over in the shop were spraying CRC on some rusted fasteners,” recalls Wilson. “Darned if some overspray didn’t get sucked into our compressor’s air intake and ruin the paint job I was working on.”

Such contamination also can be hiding on the work surface before painting, so use of a cleaner/solvent always is strongly advised.

Orange peeling is the inability of wet paint film to level out after application (Illustration 5). It can be caused by improper gun adjustment or spraying technique. This could mean too little air pressure, fan patterns too wide apart or spraying at excessive distances from the work, allowing droplets to begin to dry before they hit the work surface. It also can be caused by extreme ambient temperatures, force-drying before the droplets get a chance to flow and level out, improper flash times or, as mentioned earlier, by the wrong mix for the environment. That could mean too much – or the wrong type – of solvent causing drying before contact, too much viscosity or improper mixing.

Illustration 6 shows pinholing, which results from rapid solvent loss or moisture trapped below the paint surface. The condition can be caused by improper surface prep, air line contamination, wrong gun adjustment or technique, force-drying, excessive paint application, insufficient flash time or the wrong reducer.

Anyone who has ever been a bit heavy-handed with a can of spray paint will recognize the condition shown in Illustration 7. Running or sagging usually is the result of overgenerous paint application. Holding the gun too close to the work, or making passes that are too slow, both will do it. But it also can result from a solvent that’s too slow for conditions, or too much reducer.

Avoiding problems like these means taking the time to do the job right the first time, instead of spending even more time sanding out mistakes and re-spraying. As Parnes sums up, “Buy the best materials you can, and follow directions. There’s always a chance that something will go wrong, but if you do those two things, you’ll have a better chance of everything going right.”

Farming the job out
If you don’t have bodywork and paint facilities and technicians trained to use them, you’ll be looking for a high-quality vendor. But shop carefully. “There’s very little regulation in the commercial-vehicle refinishing business,” cautions Frank Mileto, senior vice president of business ventures, Penske Truck Leasing. “Practically anyone can call themselves a commercial-vehicle body shop. We’ve seen shops that claim to work on trucks, but they don’t even have a door large enough to get a heavy-duty vehicle inside. State-of-the-art spray booths and equipment, as well as technician training, are costly, and not many businesses can afford them.”

Mileto suggests visiting a shop you’re considering. Is it clean? Well-lit? Observe the technicians at work. Are they using correct surface-prep techniques and high-quality materials? Will your vehicle be baked and ready for use immediately after painting, or will it be air-dried and out of commission until the paint cures?

Finally, inspect the job, advises James Svaasand, Penske’s general manager of business ventures. “If it doesn’t look right, it probably isn’t. And even if it looks good, the job may not last six months, if questionable preparation techniques or cheap materials are used. You only get what you pay for.”