What We Did
Give you an inside feel on paint and body basics and show how to get it done
Don't be afraid of trying something new
What It Costs (Approx)
Prices will vary, based on experience and level of quality
When it comes to automotive painting, it's no secret that many significant changes have come about in recent years. New paints, new techniques, and new equipment are things to take into consideration when asking yourself the time-honored question: Can I do it myself?
Those of us with a strong determination to handle our own tasks will no doubt find a way to get our hands on some hammers, dollies, and paint guns and learn by trial and error how to refurbish our car's appearance. But what is the best way to feed that desire to perform some body and paint basics and where do we start? Of course the best place to start is usually at the beginning, and when it comes to basic paint- and bodywork, that means out in the driveway.
Like performance modifications, developing paint- and bodyworking skills that you can take pride in should start with the simple bolt-ons. We recommend that you save the frame-off resto or that ghost-flamed candy-pearl paintjob for a later date. For starters, it's best to take on a simple project that you can handle with a minimum of tools, and one that will allow you to see and appreciate your work by the end of the day or weekend. Once you've built up your confidence and skill level, you can move on to the bigger stuff.
Everyone has a vision of what they want their car to look like. This visualization is actually the first step of any custom bodywork or paintjob and it determines how extensive your skills must be. Before you let your imagination get too far out of control (which is an easy thing to do!), you must develop that mental image of your car while taking into consideration your skills, tools, time, and budget.
Advanced body mods are often what you see on some of the featured cars in CHP, but the very basic can be something as simple as a spoiler upgrade or other bolt-on piece from the aftermarket. A simple mod can be just as gratifying as an extensive one if done properly. Although painting and bodywork are closely related, basic bodywork is something that you can take on in your own driveway. Painting can be done in the garage, but unlike the mechanical aspects of working on your car, you must take several things into consideration. Things like compressed air, ventilation, overspray, adequate lighting, and chemical handling are often taken for granted in a shop, but could pose problems at home. The obvious answer to this dilemma was to take our basic painting needs to a place equipped with a spray booth. While some shops rent out their facilities if business is slow, we chose to seek out an institution of higher learning where beginners and pros alike can go to develop or hone their skills.
Located in a modest business center not more than five minutes from Auto Club Speedway is PPG's West Coast Training Center in Rancho Cucamonga, California. There, hidden behind a façade of what appears to be your typical small business office awaits a painter's fantasyland, rooms filled with candies, pearls, and shiny silver spray guns, not to mention a wealth of information to be had on the subject of automotive painting. The PPG Training Center is where, under the guidance of instructors Paul Stoll and Frank Ramos, students learn the latest painting techniques using the most up-to-date paints and equipment. It is no secret that waterborne-based paint technology is changing the automotive refinishing industry. This includes everything from the materials and techniques, to the equipment. We were familiar with solvent-based materials including lacquers, enamels, and urethanes, all of which have been around for decades. We were more than a little apprehensive about waterborne painting, but since this relatively new formula is where automotive refinishing is headed, our quest for a basic experience started with something new.
"Conversion with confidence" is PPG's catchphrase for change. While change in the long run is usually a good thing, the process of changing from a familiar way of doing things to a totally new one is something that we look upon with trepidation. While we may not be able to instill the level of confidence that the PPG Training Center can, we certainly hope to convince aspiring painters and skeptical veterans that this new way of painting is not really new at all. Training and education on waterborne technology and application, however, is a fairly new offering to the automotive refinishing industry. In an effort to bolster interest at the college level on how the refinishing industry is coordinating efforts with the OE's clean-air manufacturing methods and technology relating to paint, PPG established the industry's first paint training center dedicated to waterborne paint technology at China's Shanghai Communications Polytechnic in April of 2009. Since then, PPG training centers across the U.S. have adapted a similar curriculum.
While a trip to the orient might not be such a cost-effective expenditure even in the interest of furthering our car-building skills, you'll be happy to know that education on waterborne painting is available at various centers here in the United States. So to find out first-hand what this relatively new paint technology is all about, Chevy High Performance went directly to the source for an informal but very informative private session with PPG Technical Sales Instructor Frank Ramos. Frank, a veteran painter of 25 years, and I started the session off reminiscing about the good old days of custom painting with acrylic lacquers and single-stage acrylic enamels that flowed out so smoothly.
While most painters around the U.S. are still allowed to paint without restriction or regulation of volatile organic compounds (VOCs), here as well as in certain other counties of California, several states in the Northeast, all of Canada, and most of Europe are required to meet specific VOC limits by painting with waterborne basecoat materials. In order to help painters meet these requirements, companies like PPG provide training services to help painters adapt to their new system of Envirobase High Performance waterborne refinishing products.
Current and future legislation concerning VOC emissions for automotive refinishing will only reduce the amount of solvent-based paint products that we can use. One of the more popular arguments by those resisting the change to waterborne-based paints is that since the final clearcoat and many of the undercoats are still solvent-based, why change at all? The answer to that is simple. While it is true that clearcoats and many undercoats are solvent-based and will most likely continue to be so for many years, the VOCs of those coatings have been reduced by as much as 50 percent. Combined with the ultra-low VOC numbers of the waterborne basecoat materials under the clear, and you have a very clean system compared to the high-pressure, high-volume, high-VOC refinishing materials of yesteryear. Clearcoats are still solvent based due to the superior gloss characteristics and ultraviolet protection of the solvent formula.
Atmospheric benefits aside, do-it-yourselfer painters and pros alike want to know what exactly has changed and how it will affect them in terms of cost, technique, materials, and equipment. Chevy High Performance will address each of these issues here with the novice painter in mind. The answers may not be so short as to fit in a nutshell, but you'll be happy to know that the news is good; this change is fairly painless which is a good thing since, like it or not, you'll have to deal with it sooner or later if you plan on painting your street machine. But before we get into discussing what has changed, it's important to have a basic understanding of what we're getting into.
What's In the Water?
Since waterborne paints are formulated in an acrylic latex resin base, they are water-soluble. The "water" in waterborne paint reducers consists of two parts hydrogen and one part oxygen ... that's right, H20, just like your standard everyday tap and drinking water, albeit in a purified form. Does this mean that you can simply turn the valve of your faucet and have an endless supply of inexpensive paint reducer and gun cleaner? Unfortunately no, although there are probably many who have done this and will swear that it works.
PPG offers two reducers for their Envirobase High Performance (EHP) waterborne basecoat paint. Like solvent-based reducers, recommendations are based on the temperature range in which the painter plans to paint. The standard EHP reducer is Number 494, and is recommended for use in temperatures ranging from cold up to 100 degrees with a relative humidity level of up to 30 percent. Number 494 should also be used if the relative humidity is above 30 percent, no matter the temperature. A slower reducer is EHP Number 595, which should be used only under extreme dry heat conditions over 100 degrees, and below 30 percent relative humidity. Unlike solvent reducers, which can be mixed and blended at the discretion of the painter, you cannot blend the two PPG waterborne reducers to create a mid-level reducer. You must select either 494 or 595 to reduce the Envirobase basecoat paint.
Perhaps the question most often asked by painters is, "Can you drink the water?" The answer, to be on the safe side, is that paint reducers are not intended for human consumption. If there is an active ingredient in the waterborne paint reducer, it is a chemical called butoxyethanol. While the name may be unfamiliar to you, this is simply an organic solvent that is commonly used as paint thinner and is also found in some ordinary off-the-shelf household cleaners. Butoxyethanol is non-toxic enough for the EPA to have removed it from its list of hazardous air pollutants over 15 years ago. Waterborne paint reducer has also undergone a process of purification known as de-ionization. Water that has been de-ionized will contain no significant traces of mineral ions that could adversely affect the paintjob. Using PPG's specially developed Envirobase reducers will minimize the possibility of contamination, de-lamination, discoloring, and rust spotting.
What Is A VOC?
We've established that waterborne automotive paints and undercoats are nothing new. However, it's more likely that the first water-based primers were introduced not necessarily to comply with VOC regulations, but to offer an option for the painter who was having compatibility problems with unknown undercoats and sensitive lacquer topcoats. Because a waterborne primer can effectively serve as a barrier coat between incompatible solvent-based products, painters have been using water-based undercoats for many years. For example, R-M (now BASF) first introduced an easy-sanding waterborne barrier coat back in the late '70s that, according to paint reps, allowed a fast-drying topcoat such as lacquer to be applied over fresh or uncatalyzed enamel without having to strip the surface. Due to its water base, VOC content was lower than that of solvent primers, but there was never any mention of the clean air emissions back then.
While the barrier effect is still a benefit of some waterborne coatings, the primary objective with today's paint is to reduce the emission of harmful solvents into the air that we breathe. In California, the agencies responsible for determining what is safe or not are the California Air Resources Board (CARB) and the Air Quality Management District (AQMD). On a federal level it is the Environmental Protection Agency (EPA). In light of all of the relearning that is now required in the painting industry, it's natural for painters to hold a little resentment to these agencies, but the bottom line is: they are only looking out for our better interests.
If you were to attend class at the SoCal PPG Training Center, instructors Paul Stoll and Frank Ramos will tell you that volatile organic compounds are a class of materials that include most of the evaporative solvents used in automotive refinishing products. We won't get into specific ingredients since most of them are known by their chemical brand name, but suffice to say that VOCs are found in all primers, sealers, paints and toners, clearcoats, hardeners or catalysts, reducers, and cleaning solvents. There are non-VOC solvents available; however, they tend to evaporate quickly thereby increasing the cost factor and do not always provide the best results.
A volatile organic compound is measured by its weight. For example: A typical gallon of automotive refinishing reducer contains 7 pounds of VOCs. Considering that a gallon of water weighs in at approximately 8.3 pounds by comparison, 7 pounds of VOCs per fluid gallon is a lot! Basecoats that use VOC-containing solvents have a VOC content of 6.0 to 6.6 pounds of VOCs. The new rule for most areas in California (and with many other states soon to follow) is 3.5 pounds of VOCs for basecoats and 2.1 to 2.8 pounds for primers, sealers, and clearcoats.
Water vs. Solvent
OK, that heading might be somewhat misleading since this is not a competition per se. There are numerous and significant changes between solvent basecoats and waterborne basecoats in preparation requirements, spraying techniques, and overall visual characteristics of the coatings. These are the areas that painters will be most interested in. Preparation includes all of the steps required in order to get the surface ready for the basecoat and clearcoat. Cleaning, body repair, metal prepping, material removal, and abrasive treatments, primer, and sealer application all fall into the prep category. There are many variables involved in each stage of preparation, and not all of them may apply to the topic of waterborne application. So what we will focus on here are the methods that might require some relearning on behalf of the individual painter.
One of the main differences that you will notice with waterborne basecoats is that its dry film is thinner than that of solvent paints by as much as 50 percent. The higher solids of a solvent basecoat tend to fill more of the surface irregularities such as sanding grit marks and even small pinholes. Because the thinner dry basecoat film will conform to the surface and reveal those irregularities, final sanding with finer grit is an absolute necessity. It is not uncommon to machine-prep (always with a pneumatic dual-action random orbital sander; no fixed orbitals or electric sanders!) a surface for solvent basecoats with sanding grits in the 220 to 240 range, with hand sanding done with 320 to 400 grit. In preparing a surface for a coat of waterborne Envirobase HP, PPG recommends hand-sanding most new OEM replacement panels with 400 grit (by machine or hand) prior to sealing for waterborne basecoats. If no sealer coat is required, you can simply scuff-sand the panel with 600-grit prior to base coating. As with all standard prepping methods, you should avoid breaking through the factory sealer coat and exposing any part of the bare panel.
A non-sanding sealer is applied onto the sanded panel for two primary reasons: to provide a uniform substrate for the waterborne basecoat color coverage and to enhance the quality of adhesion. Instructor Ramos emphasized the importance of maintaining the correct sealer coat thickness as well as color uniformity in order to achieve a good color match. Too thin of a sealer will most likely cause the waterborne topcoat to lift (lifting appears as a wrinkling of the paint coat and is caused when solvents are either incompatible or are allowed to penetrate a sealer of insufficient thickness). Once a proper sealer coat has been applied and allowed to flash dry for the recommended amount of time, the waterborne basecoat can then be sprayed.
Experienced painters often dabble in mixing and matching products from different paint manufacturers, sometimes out of necessity to avoid wasting the materials that are already in the supply cabinet. Due to the sheer number of different products from the various paint companies, we can't even begin to touch on what will work with what. What we can say is that by sticking to a paint manufacturer's system of products, you can greatly reduce the variables and potential problems.
Application techniques for waterborne basecoats are similar to those of solvent basecoats, which helps to make the conversion process fairly painless. There are some differences though, so having a fundamental understanding of painting techniques along with common painting terms and methods will certainly help to understand the conversion process. It should be noted that the techniques that we will talk about here are specific for applying PPG's Envirobase HP waterborne basecoats. Application methods for other manufacturers' waterborne-based paints might be different. For instance, Ramos, who is also certified with the DuPont and Sikkens paint programs, explains that DuPont waterborne basecoats are applied wet on wet, whereas the PPG Envirobase HP base is applied when the previous coat has flashed to a dull, flat finish.
Although the toners in the Envirobase HP paint mixing system are formulated to give precise matches to OEM colors, there are certain steps to follow in order to get there. First is adequate coverage over the correct shade of sealer, which is accomplished with what PPG refers to as the "coverage coat." As mentioned earlier, the sealer must have adequate film thickness (but not too thick), and the shade must match PPG recommendations; the shade of the sealer ("shade" referring to darkness or lightness as opposed to hue) should match the base color as closely as possible (i.e., light-colored sealer for light colors and vice versa). Sufficient coverage over the sealer is attained when there is a uniform opacity; usually two coats. Distance from the surface during the coverage coat is 6 to 8 inches with an overlap of 75 percent. Air pressure is critical, but unlike solvent-based paint, each spray gun manufacturer has a specific air pressure recommendation.
Coverage and Control
Automobile manufacturers have been using waterborne paints for many years for the same reasons that the refinishing industry has been making the change: low VOC content and faster performance. The difference between the factory paint and that which is applied at a body and paint shop is that the OEM paint is applied electrostatically. When metallic colors are applied in this manner, the metallic particles or flakes are immediately locked in place by a static charge. Unfortunately, this is not possible when paints are applied on a refinishing level, so in addition to the coverage coat, metallic paints (as well as pearls and some special effects colors) require a "control coat." The control coat determines the accuracy of the color match and a uniform distribution of flakes that matches the factory finish. Without the electrostatic process, flake particles tend to sink with each layer of the coverage coat. The Envirobase HP control coat is what you might refer to as an "appearance coat." Properly applied with a consistent 80 to 90 percent overlap (Yes, 90 percent is almost a double-coat per pass!) at a distance of 10 to 12 inches and air pressure lowered by approximately 40 percent, the control coat keeps the flakes on top, rendering the same appearance as an OEM finish.
One of the most challenging obstacles for a conversion painter to overcome at this point is how to determine whether the metallic pattern is even and, if spot painting, making sure that the color and metallic pattern matches the existing finish. Because of the matte appearance that the waterborne base takes on when it flashes dry, the visual aspect of determining color-match accuracy and proper surface texture is no longer reliable. The painter must rely on the knowledge that you have selected the correct sealer, mixed the base color accurately, and applied the correct spraying technique during both the coverage and control coats because until the final clearcoat is applied, the basecoat will have an orange peel texture to it and the color will not take on its true tone even under ideal lighting. The tried-and-true painter's practice of simply dipping the mixing stick into the paint to check for color-match accuracy is also out the door with waterborne base colors.
For painters who are just starting out with waterborne paints, Ramos highly recommends using the viscosity cup during the mixing process to assure correct reduction of the paint. Incorrect viscosity such as a mixture on the thin side will result in a topcoat separation that takes on the appearance of the dreaded fisheyes. For those that have no prior background in solvent-based painting, textbook procedures such as this are good to learn and should be made part of your regular mixing routine.
The mechanics of building a street machine sometimes hold enough of the unexpected to challenge even the most devout DIY-er. Enter the painting arena and the variables can and often do increase exponentially. Add to this the constantly changing chemistry of paint materials to accommodate new OE colors as well as the limitations set forth by air quality management agencies, and painting can turn into quite a challenging task. As automotive technologies progress, it is the ongoing job of our clean-air agencies to observe that progress and find new and better ways to keep our world clean. Sometimes, it's not easy to accommodate the changes that come about, but when change is inevitable, it's usually better to embrace them rather than to resist.
Cost And Quality Comparison
We had a unique opportunity to see the difference between a single-stage, solvent-borne color versus the same color formulated with Envirobase HP waterborne-based paint. We ordered a quart of Omni (PPG's economy paint line) from a local paint supplier with the understanding that this would be a single-stage paint with no clearcoat. We were also advised that this particular color formula (Corvette Arctic White) might not provide as good a color match as the waterborne Envirobase High Performance waterborne basecoat/clearcoat system would. We thanked them for their advice and proceeded to paint the parts with the solvent-borne, single-stage paint.
The Omni single-stage paint formula consisted of the same four toners as the Envirobase HP basecoat/clearcoat formula, however, as our paint supplier predicted, we noted that there was a slight color variance under certain light. The accompanying photo shows that difference especially with the license plate frame. The Omni color match passed the inspection of most who saw the job, but discerning eyes noticed the brighter shade of white on the repainted parts. The gloss and texture of the Omni single-stage was beautiful, however, this type of paint was not intended to give a precise panel-to-panel match.
The Envirobase HP basecoat system is designed to provide an exact color match to the OE finish. Specific sealer, an extensive selection of basecoat toner formulas, and the VOC-compliant clearcoat help the painter accomplish this.
We observed how Ramos performed the entire PPG process of repainting our Corvette parts with Envirobase HP from searching the database for the correct color formula, to prep, to final clearcoat. The entire process was completed in a mere two hours! After a break for lunch, the clearcoated pieces were not only dust-free ("dust-free" is a term meaning that the surface has hardened enough so that dust will not embed into the finish), but the parts were ready to be handled and installed.
While paint and body shop fees can vary depending on the type of shop, its workflow, and even location, the cost of paint materials is something that we can compare somewhat objectively. The total cost of the Omni materials for painting the aftermarket C6 spoiler came to $88.54 from our local automotive paint retailer. This included one quart of the Omni urethane base color (single-stage, no clearcoat required), one pint of hardener, and one quart of reducer. The material cost for the same spoiler from the same retailer for Envirobase came to $376 for one pint of waterborne basecoat paint, one gallon of 494 reducer (if 595 reducer was needed, add an additional $15), one gallon of EC700 clear (no smaller size available). And one quart of ECH7080 medium hardener. Is the Envirobase system worth the additional $300 for this small paintjob? In terms of reproducing the OE finish with a precise color match, absolutely!
The Right Tools For The Job
It's probably safe to say that most car guys share a unique addiction to tools. We all love to get new tools! And while having the specialized equipment designed for the application of waterborne paints is not an absolute necessity, we certainly won't pass up an opportunity to expand on our ever-growing collection of tools.
As always, safety and health should be of primary concern and having the proper safety gear for all types of painting is an absolute must. While waterborne paints are generally considered safer than solvent-based coatings, no paint is absolutely safe so precautionary measures need to be taken throughout the entire process. You should always consult the Material Safety Data Sheet (MSDS) for the product that you are using, and read the supplied product information sheet from the paint manufacturer to make yourself aware of any potential health hazards. A painter's safety gear includes an NIOSH-approved respirator or positive-pressure fresh-air breathing system, eye protection, gloves, and a paint suit. NIOSH is the National Institute of Occupational Safety and Health, and all safety gear that meets the institute's approval will be clearly marked so. Respirator masks should always be fitted properly to the face, and those who of you who sport a beard or goatee should use a full-face hood. Respirator masks should always be stored in an air-tight storage bag, and fresh cartridges should be installed prior to use. If you detect any trace of a chemical odor with a respirator on, stop immediately and repair or replace your mask.
Personal protective gear should always be worn during all phases of the paint process including preparation and sanding, paint mixing, spraying, and gun cleaning.
As you can see in the accompanying photos, PPG instructor Frank Ramos wears the appropriate safety gear during each phase of painting. The PPG Training Center is a state-of-the-art facility and their paint department is equipped with the Sata Vision 2000 positive-pressure respirator for students and instructors alike. Wearing a full suit and respirator with belt attachment may take a little getting used to, but you should never compromise your safety or health for comfort.
The Spray Gun
The last significant change in the design of the automotive paint spray gun was the switch from siphon-feed regular-pressure guns to the high-volume low-pressure (HVLP) gravity-feed design. Some gun manufacturers still make siphon-feed guns with HVLP output, but the majority of painters are using gravity-feed guns with the cup positioned on top.
The use of waterborne paints requires a slightly different version of the HVLP gun. All of the major spray gun manufacturers now offer a line of spray guns designed for use with waterborne paint. Gun components must be resistant to corrosion due to the constant exposure to water. Sata offers their top-of-the-line Satajet 3000 HVLP Digital with corrosion-resistant components and a handle plated with chrome. Needle sets are stamped with a "WSB", which indicates use for waterborne materials and will feature a special 1.3mm fluid tip. Other gun manufacturers like Devilbiss also offer waterborne spray equipment; their popular Gti HVLP gun has been outfitted with special internal parts, a distinctive blue handle, and is re-designated Gti-W, for waterborne.
Since most painters have already invested a good chunk of change in spray guns for solvent paints, you might be wondering if it is absolutely necessary to update your guns for waterborne use. Well, we experimented a little and sprayed some waterborne primer through a non-waterborne gun and found that although it will work initially, we noticed an immediate deterioration on the surface of some of the internal components as well as the gun handle itself. And this occurred even after a thorough cleaning; all moisture was removed, gun-cleaning solvent was sprayed through the gun and it was oiled right after use. It wouldn't take long for the corrosion to affect the precision function of the needle and other mechanisms inside the gun. So we highly recommend investing in a spray gun designed for shooting waterborne paints.
When paint materials are properly reduced and ready for application, they must be poured from the mixing vessel into the gun cup. This is a process that can transfer unwanted particles into the gun, which can and often does have a negative affect on the atomization and fan pattern of the material being sprayed. Worse yet, unfiltered particles have a way of passing through the gun and splattering on a most conspicuous spot on a car. To reduce the chances of this happening, filtering, or straining, solvent-based paints, primers, and sealers into the gun has been a standard procedure for many years. Most paint suppliers usually furnished complimentary paper filters with the purchase of any paint. Those cone-shaped disposable paper filters are still good for your solvent materials, however, you might need to set them aside when loading water-based paints into your gun. Since many of those paper strainers are constructed with a water-soluble adhesive holding them together, they may literally fall apart when used to strain waterborne paints. Also, the filtering mesh is most likely insufficient for screening out foreign particles. While solvent-based materials are typically filtered at 200 microns, a waterborne paint strainer must provide filtration down to 125 microns. 125-micron paper filters are intended for use with waterborne materials such as Envirobase HP and will most likely not come apart, however, you should check with your supplier prior to use.
The drying characteristic of waterborne paint is entirely different from that of solvent basecoats. Heat via climate control or heat lamps is no longer an effective means for accelerated drying (unless of course, you are spraying solvent-based coatings). Waterborne paints require air movement to effectively evaporate the water content in the paint film. Spray booths can be retrofitted with large air dryers for high volume work and complete paintjobs, or painters can use handheld air dryers for smaller spot repair jobs. Hand dryers such as the Sata Dry Jet features a fine screen to prevent foreign matter in the airstream from passing onto the surface, and consume approximately the same amount of air as a spray gun, and the pressure can be adjusted to suit the application.
Body Shop Basics: Grits & Grinders
Handling our own bodywork and/or preparation for paint can be easily accomplished at home with a minimum investment in tools and materials. Pictured here are all the tools and materials you will need to handle a basic body repair such as a small dent or high spot. Having compressed air is a luxury for some of us working out of our garages. While most pro body men and painters prefer pneumatic power, electric or cordless grinders and sanders are more practical and affordable for home use. One of the prohibiting factors of doing body repair or paint prep at home is the lack of compressed air. Fortunately, companies such as SEM offer good quality aerosol undercoats for bodywork and paint prep, eliminating the need for spray guns and an air compressor.
Whether it's a very basic body mod such as a bolt-on spoiler or body kit, or a more advanced procedure requiring repair to a dented panel, all bodywork and paint prep involves the use of a variety of abrasives. Part of the key to saving money is learning how not to waste it by knowing what the different types of sandpapers are for and what grits are used for preparation.
One of the first steps to successful and cost-saving DIY bodywork is to familiarize yourself with sandpaper grits as well as types of sandpaper and grinding discs. There is a purpose for each grit and type of sandpaper but you'll be glad to know that you won't have to buy them all. Below is a rundown of the more common paint and body sanding grits and what they are most often used for.
The Cheesegrater: Sometimes referred to as a rasp, this inexpensive tool is not really an abrasive but it is the most effective tool for shaping body filler. Knowing how to use the grater is an acquired skill similar to block sanding, and using it the right way will save time, effort, and abrasive materials after you begin to sand. The grater can be used for rough-shaping and for removing the glaze on the surface of catalyzed body filler that clogs sandpaper.
24-, 36-, 40-grit: Although a coarser 16-grit is available, 24-, 36- and 40-grits are usually coarse enough to handle most material removal requirements. A variety of sizes are available but small repairs can be performed with a 3-inch and a twist-on or pressure-sensitive adhesive (PSA) 3-inch pad on a 90-degree die grinder or cordless drill. Larger areas can be worked with a larger disc on a high-speed sander or a random orbital sander with 6-inch pad.
80-, 100-grit: These are intermediate grits that are often used for light material removal and final-shaping of body filler prior to applying any type of primer. When shaping body filler, the repair spot must be perfectly straight before proceeding to finer grits. The transition from body repair to paint prep occurs at the point where grits in this range are used.
120-, 150-, 180-grit: Feather-edging is the process of leveling the existing layers of a finish where grinding has occurred. Always begin with the coarser grit first, and gradually progress to finer grits as the quality of leveling improves. Trying to feather a coarse paint edge with 180 first will only result in smoothing out the edge, not leveling it. 120-grit is the best grit for leveling layers of existing paint and undercoats.
220-, 240-, 280-, 320-grit: Again, working from coarse to finer, these grits are used for block-sanding primer coats to eliminate the subtle waves and imperfections from a panel. The condition of the body and also on the paint color (darker colors, pearls, and metallics tend to show more imperfections than light, solid colors) will determine how much block sanding will be required.
400-, 600-grit: These grits are considered final-prep grits for sanding undercoats, OE sealer, or an OE paintjob prior to paint. The type of basecoat you plan on using will determine what grit to use. Remember that waterborne basecoats have a thinner dry film buildup and require finer sanding grits. Solvent-based urethane basecoats and lacquers can be prepped with 400- to 500-grit, and acrylic enamel topcoats can be prepped with 220- to 320-grit.
Sandpaper grits in the ultra-fine range are used primarily for cutting and buffing to break down any unwanted texture in the finish, referred to as orange peel, or remove any tiny dust particles that may have found their way onto the wet surface. This is followed by compounding and polishing with a buffer. Originally, grit numbers were a rating system that indicated how many grains of the abrasive would fit along a one-inch line. If only 36 grains could fit on the line of reference, it was labeled 36-grit. If you look at and feel a sheet of 36-grit paper, the grains are large. By comparison, you cannot see or feel the individual grains on a sheet of 2,000-grit paper.