By Carl Wilson for BodyShop Business
I suspect most painters have spent time as a helper before they ever got the opportunity to paint. Therefore, they should be the perfect people to train and mentor young men and women just coming into the industry — theoretically, anyway.
Unfortunately, many painters will be stingy with their experience and expertise, perhaps because they were forced to attend the “School of Hard Knocks” and there’s no way they’re going to freely give their hard-earned knowledge away to their future replacements.
As a result, we often have helpers struggling to make the car ready for paint because they’re simply not aware of the fundamentals, the how and the why, or the mission.
Fortunately, various companies within the industry that make everything from abrasives to paint have best practices that are published and available. Their websites have a plethora of resources for guidance and study.
While it’s true the techniques are many and the fundamentals are few, I’m going to teach a new helper a specific technique within specific parameters, staying faithful to the fundamentals in order to achieve the desired outcome. After the helper has a grasp of the fundamentals (the how, the why and the mission), they can then alter the technique if the situation calls for it, providing they stay within the established parameters — without having to come ask me how. The goal is to give them the knowledge to enable them to make the best decision the situation calls for — because our ultimate goal is to develop this newbie into a valuable, thinking member of the team.
- Initial cleaning
- Priming (used generically to include primers and surfacers)
- Block sanding
The “why” is to remove as much of the contaminates as possible so as not to drive them deeper into the finish’s pores while sanding. A clean panel also allows us to more clearly see any additional damage (scratches or chips) we may or may not need to address. The “how” is with multiple cleaners; first, a waterborne cleaner to eliminate any naturally occurring contamination such as bird poop or dirt, followed by a solvent-borne cleaner to eliminate man-made contaminates such as road tar or waxes.
Start with putting on gloves and use two cleaning towels. Avoid the “glug-glug” method of saturating a towel and instead use a pressure sprayer to spray the panel. The cleaning solvent will loosen and float contaminates which you encourage with the first paper towel, wiping in a pattern that avoids back-tracking. This is immediately followed with the second towel to dry it; avoid letting the solution dry on the panel. Two towels. You don’t dry dishes or your car with the same rag you washed with, do you? No, you don’t. Use two towels here too.
When the panel has body filler, clean as stated on the unsanded portion of the panel. On the filler itself, use only the waterborne cleaner after blowing it off, and then blow any residual cleaner dry after wiping it off. The “why” is to remove any sanding dust left by the bodyman and allow for a better inspection.
The “why” is to identify anything additional that needs to be done up-front repair-wise, and to check that the repair meets our quality standard. The “how” is carefully and with purpose, with a clear understanding of the standard.
A clean panel and adequate lighting is essential for inspecting. We’re looking for any scratch, chip or ding that may have been missed. Find it and ask the question now, “Are we fixing this?” Some shops have a policy of fixing chips and scratches that are within the blend zone of color. Some do not. Either is fine as long as everyone including the customer knows the policy and what to expect. We’re also looking for pinholes or coarse scratches in the body filler. Use a flashlight with the side-light technique to emphasize any discrepancies. See Photo 1. Refer to the technical data sheets (TDS) of the primer you’re using to determine the appropriate sand-scratch to prime over. Do not ask the primer to do more than it was intended to do; doing so invites problems downstream.
Feel the repair for straightness; a helper will typically need time to learn this, although some will pick it up quickly. A paper towel between your hand and the panel will lessen the influence of differing textures due to sand-scratches and will minimize false readings. If the repair meets the standard, then we proceed in the paint shop. If it does not, then we need to address it – now, before we go any further.
The “why” is to provide a mechanical structure to facilitate adhesion as we minimize the sand-scratch signature the bodyman gave us at the edges of the repair. The “how” will follow, and we won’t get into the various opinions regarding grit choices or wet versus dry sanding but simply refer you back to the best practices outlined by your paint and/or sandpaper manufacturer. We’ll talk about the fundamentals of sanding, both with machine and by hand.
We’ll focus on the familiar “DA,” and I put that in quotes because most DAs today are not true DAs (dual action). Most mechanical sanders today are simple orbital sanders, which is fine. The original DA had the ability to lock out the orbital function and be something more like a hand grinder, hence the dual action. In the paint shop, it was most always used in the orbital mode. In years past, the jitter-bug (an orbital with a rectangular sole that used one-third of a sheet of 9×11 sandpaper) was also used but seems to have fallen out of favor in the paint shop.
The main rule when using a DA is to keep it flat. There are times when the edge can be used, especially when you have skill with it, but new helpers need to keep it flat! One exception to this rule is when the DA is fitted with an innerface pad, or the soft, spongy, half-inch-thick pad sandwiched between the hard pad and the sandpaper. Because it’s soft, it’s forgiving and won’t dig the way the edge of a hard pad will. Another rule is to stay away from body lines and edges – save those areas for hand-sanding or scuffing. This will help prevent sand-throughs on blend panels in areas where we don’t want to put color.
There will be instances when sanding with your actual hand or thumb instead of a backing pad is desired, such as in the finger-well under a door handle. Generally, though, you should wrap the sandpaper around either a hard or soft sanding pad, depending on the circumstances. Even an old, used piece of scuff pad can make a decent backing pad. The point of the pad is to avoid cutting finger grooves in what you’re sanding. When we use a scuff-pad only, without the assistance of sandpaper, we refer to this as scuff-sanding. This is primarily used on blend panels.
The “why” is to provide a suitable surface for painting. The “how” begins with the body work meeting our quality standard.
We cannot fix poor body work with primer. Again, we cannot fix poor bodywork with primer. One more time: we cannot fix poor bodywork with primer. With rare exception, the appropriate body filler should be level with the substrate — the steel, aluminum or plastic. The filler should not be applied over the edge of the paint but directly to the substrate. The sanded paint edge should be “feathered” about one inch per previous paint job, so if it has been painted before, the feather-edge should be about 2 in. wide. See Photo 2. The function of a true primer is to prepare the substrate for the next coating. The function of a primer/filler or surfacer is to build the film thickness up over the repair, so that after sanding we have a flat surface that transitions from the undamaged field of the panel, across the featheredge and over the repair.
Presuming the body work is ready and we’ve already cleaned, inspected and sanded, we now mask for prime. This is masking designed to prevent primer and overspray from getting on the vehicle anywhere but where we want it. It’s a separate operation from our final masking, and you should charge for it.
It is generally a bad idea to attempt to control overspray by lowering the air pressure as this results in poor
atomization and excessive texture. See Photo 3. Refer to the TDS for proper air pressure and application specific to the system you’re using. Generally, it will call for three medium-wet coats with proper flash time between coats. Proper flash time is a principle to learn now, as habitually disregarding it will cause problems that consume more time than it saves. The TDS will likely say something like “…three coats with a five- to 10-minute flash time between coats…” If we consider the actual spray time combined with the flash times, we have a theoretical minimum of 15 minutes for a priming operation, and likely longer. Do not allow the helper to think that they can be done in seven minutes; the person who’s done that fast is likely rushing everything — sealer, color and clear — compounding the problems downstream.
Lastly, apply the primer with the “outside-in” technique to avoid any chance of air entrapment at the primer’s edge. Many of us learned decades ago to do an “inside-out” technique because we were using lacquer primer, which is reversible and therefore the edge would melt with each subsequent coat. Not so with 2K primer.
The “why” is to sand down the primer to be even with the surrounding paint film. The “how” is with a “block,” which will allow us to cut any high spots flat while bridging over any low spots until we have a flat surface. Start with applying a guide-coat, which allows us to visually “read” the progress of our sanding. The camp seems to be fairly divided between spray-on guide coats and powdered guide coats. My advice here based on more than 30 years of hands-on experience in a paint shop is to use the powdered product for a variety of reasons: no overspray, no fumes, better coverage of the area to be sanded, and it doesn’t load the sandpaper the way a spray-on guide coat will.
Using the longest block practical loaded with an appropriate grit sandpaper for cutting (as opposed to smoothing), sand in a cross-hatch pattern. Top left to bottom right, followed by top right to bottom left. Alternating between these two directions as you sand across the repair helps prevent cutting a groove or pattern in the primer. Continue sanding and “reading” the guide-coat until the guide-coat has been sanded off, or a high spot of substrate or body filler has been revealed. If a high spot appears, then the helper will need to get an experienced opinion from the painter as to the next step – keep sanding, re-prime or send it back for further work from the bodyman. This can serve as a learning opportunity for the helper, illustrating why the inspection step is so important.
If the guide-coat sanded off without any sand-throughs of the primer, then more guide-coat is applied. We switch to a finer grit sandpaper and proceed to eliminate those first-cut sand scratches. Continue with this process until you’ve achieved a sealable/paintable sand scratch. The painter may want to introduce a DA with an innerface pad, or a soft hand-pad for the final sanding. The trick is to always leave enough primer for the next grit of sandpaper so that the finished product is flat and not a dished-out low spot. Expect a few re-primes as the helper is gaining skill here. Advanced block-sanding will include concave and convex surfaces as well as bodylines. Let’s teach the helper how to properly block a flat panel first.
The “why” is to prevent panels adjacent to the repair from being painted, and also to prevent drifting overspray from landing on the vehicle. These two goals here give us two specific approaches: first, masking the critical edge (the first six to 12 inches immediately adjacent to the panels we will paint), and second, covering the car. The critical edge will include the jambs when necessary.
The “how” begins with cleaning the panels again to remove all sanding dust and produce a good, clean surface to facilitate adhesion of the masking tape. With this cleaning, a waterborne cleaner is sufficient. Use the pressurized bottle to spray the panel, and then proceed with the two-towel system discussed earlier, making sure all jambs and edges are dry. Proceed to the next panel and repeat until finished. Now, blow the panels off to remove any towel particulates that may have broken down off the wet towel. At this point, I wash my hands. I don’t want dirty hands contaminating my clean panels or leaving any powdered guide-coat smudges. The critical edge is masked when the vehicle is parked outside of the booth. The car is covered once the vehicle has been pulled into the booth.
There are many techniques for masking the critical edge: back-
taping, folded tape trick, soft foam, paper or plastic. There are a few techniques for covering the car: multiple sheets of 36-inch paper, plastic car covers or spray-mask. Therefore, it’s vitally important that the painter is actively communicating to the helper what the preference is and coaching him to achieve it.
Keep in mind that the best lighting is typically in the booth, and that is where we generally see the shortcomings of prep and masking. This is why the use of auxiliary lighting during earlier steps is strongly suggested.
Buffing and Plastics
Rather than diving further and encompassing buffing and plastic preparation here, I suggest we get the already-mentioned fundamentals ingrained. The chance for failure is too great with raw plastic if cleaning isn’t performed correctly and burned edges if we press the unskilled hands of the helper into the buffing operation prematurely. The fundamentals – cleaning and sanding – can be augmented with the specifics regarding plastic and buffing after they’ve been mastered.
The mission in the paint shop is to properly paint cars as fast as possible. To do this, we must be accurate in our operation, which means doing things correctly the first time. For a helper to prepare cars to our expectations, they must know what the expectations are and how to get there. They can get there every time with the fundamentals, provided we’re not stingy with our knowledge and take the time to train them properly.