Professional Techniques for One-Of-A-Kind Custom Automotive Painting
The scope of this article aims to cover the most pertinent information you need to know when considering becoming an automotive painter. A broad view of each stage of auto paint production with common problems equip you with a general idea of what you will be facing and things you need to consider. While generalized, these principles can be applied to the vast majority of paint work you could be tasked with. This can be thought of as a step by step guide to auto painting, with each phase of painting being discussed from start to finish. Specific topics will be explored in depth in their own articles, with material considerations and techniques explained in a thorough and focused way. This article aims to give a broad overview of custom automotive painting, but if you’re looking for a quicker read check out Car Paint Spraying Techniques in 10 Steps.
Key Topics
- Priming: The importance of getting the primer *just right* is critical to the overall outcome of the paintjob. This foundational layer protects the material being painted, and gives the paint layer strong adhesion.
- Wet Sanding: A specialized form of sanding that uses waterproof sandpaper and water to create a clean, uniform surface, finished to fine scratches to ensure adhesion, evenness, and avoid drips & runs in the paint.
- Surface Preparation: Proper inspection and preparation of the surface, after the “rough work” has been done is needed to give you the best possible finish in the first try. Last minute fixes, thorough cleaning, and inspection techniques are covered here.
- Spraygun Setup: Understanding the complex machine that will be the central tool of your paint shop is the difference between amateur hour and a show-winning stunner. Setup your spraygun and equipment like a pro, get started on the right foot.
- Paint Application: Air pressure, fan width, paint volume, spray pattern: many subtle calculations go into producing the perfect paintjob. Remove the mystery of this fascinating art with our time-tested techniques.
- Single Stage or Base Coat: Two types of color coats dominate the automotive painting industry: Single Stage, and Basecoat. Both have their advantages, and we will explain the differences and when they are best used.
- Clear Coating: Add shine (or maybe matte?) and a protective layer to your paint. More than simply an aesthetic gloss, clearcoat seals in the basecoat, protecting from the elements and prolonging the life of the paint.
- Drying and Curing: Weather, humidity, and temperature can all have adverse effects on the way your paint dries. Depending on your circumstances, heaters or dryers may be necessary.
Priming for Success: Primer as the Foundation of Perfect Auto Paint
Selecting a type of primer relies entirely on the material you wish to paint. Automotive painting requires you to be adaptable, with no shortage of a variety of materials. While steel, aluminum, plastic, and brass make up the vast majority of what cars are made of, you may find yourself up against wood, lead, cast iron, leather, fabrics, and so on. Customers will never fail to surprise you with what they ask to be painted, so you should be ready to accommodate all of their whimsical desires (within reason and budget range). While there may be primers out there advertised as a “one primer does it all”, this unfortunately is never the case. Each material requires special considerations: both the parent material to be painted, and the subsequent paint and clearcoat layers need to be factored in when choosing your primer.
Etching Primers for Metal: a Chemical Necessity for Correct Adhesion
Steel and aluminum are the most common types of metal you will be painting, with brass and lead poking up occasionally. Particularly in older vehicles, lead was used to solder major portions of the body sections together to provide a strong and slightly flexible joint. Brass is another metal used in older production vehicles, sometimes even polished as a decoration. Brass parts under the hood will often be painted black or the same color as the engine block, based on historical accuracy or style. Regardless of metal type, they need a good soak with etching primer anywhere there is bare metal. Self-etching primer contain acids that “bite” into the metal on a molecular level, etching itself into the microscopic pores of the metal surface. Because of this, etch primers can have as acrid smell that’s similar to vinegar and rotten eggs mixed with magic markers. This distinctive stench is how you know it’s working, as it embeds itself into the very grains of the metal surface. This of course assumes that you have prepared your piece to clean metal, covered extensively on our page about Rust Repair.
The Stench is How You Know It’s Working
Depending on the desired finish, self-etching primer may be sufficient to paint over without the need for further priming, such as on parts that make up the undercarriage and various brackets. Care should be taken when sanding or scuffing the etch prime to avoid removing it to bare metal. If painted within a certain time window, most etch primers can be painted with a top coat without the need for further preparation, although if it is completely dried and cured it needs to be scuffed and cleaned again. From personal experience, results are best when the entire bare metal surface is completely covered with etching primer, and should any metal be exposed during the preparations before final paint, it need to be touched up with etch prime in one or two thin coats. Before adding another type of primer, before even adding body fillers, the metal should be completely etched. Due to the nature of its chemical processes, sprayguns used for etch prime will become permanently spotted and stained, adopting the color (usually drab green) of the etch primer of your choosing. Getting a Cheap Spray Gun that is dedicated to etching primer is the only way to go. Trying to clean all of the etch primer out of the same gun you use to paint with will end up costing you a tremendous amount of time (time=money), and that’s not even talking about the chance of a big ugly booger of primer that you couldn’t quite get out of the tiny crevices winds up in your very expensive top coat. The gun should be cleaned after use regardless, but with a dedicated spraygun you are protecting yourself from major screw-ups in the final layers. Getting a clump in the primer layer is not a big deal, you can always let it dry and sand it a little, usually without the need for more primer.
Epoxy Primers: a Symphony in Two Parts
Epoxy primers are colloquially known by many names, like high build, high solids, filler/sealer, and so on. Essentially, these epoxy primers come in two parts: the primer itself, and an activator. The amount of activator needed differs by brand, but generally much less activator is needed than primer, so the two parts will come in different sized containers. Primer/sealers are usually on the thinner side, meant to literally just seal up a previously painted surface that has been worked on. This allows the surface to have one even consistent layer for the color coat to adhere to, as opposed to simply painting right over the spots of etch primer (you did put etch prime on all your exposed bare metal, right?) . Sealer also prevents any adverse reactions between the freshly sprayed paint full of “hot” solvents, and any of the original paint, body fillers, or self etching primer. Flare-ups can occur around edges where material has been sanded thin, allowing the fresh solvents to penetrate the matter beneath it, causing wrinkles and expanding/shrinking. Primer/sealer solves this costly disaster. Most epoxy primer/sealers can be used to prime plastic directly, although certain types of plastic might require a coat of adhesion promoter before applying primer.
Do Me a Solid: High Build High Solids Primers
High solids/highbuild/spray fillers are as you can imagine heavier bodied and more viscous. A spraygun with a larger nozzle are required for these types of primers. Don’t think you can get away with loading up this stuff into the same gun you use to spray your color, you will surely regret it on both accounts, as the smaller nozzle wont allow for the primer to flow properly, it will become clumpy and runny, and most likely dislodge itself in a slimy clump into the top coat. Just like etching primers, epoxy primers need a dedicated spray gun. If you really want to be a minimalist, primer/sealer can be sprayed from the larger-tipped high solids spraygun, but you will need to tune it waaaay down so you dont end up with a puddle on your piece. A better strategy is to get a Cheap Spraygun Set from Spraygunner with large and medium nozzle spray guns, used only for spraying epoxy primers. Once again, the amount of wasted time, effort, and cleaning solvents, you will be more productive and save more money in the long run by having a sprayer for each type of paint .
Don’t Be Afraid of the Water: Dive In To Wet Sanding Auto Paint
There have been heated arguments in paint and body shops around the world disputing the benefits and advantages of wet sanding vs dry sanding, but without fail, when done correctly wet sanding produces a smoother, cleaner, and more paintable surface. Take my personal anecdotes as you will, but over the course of my professional painting career I have thwarted many anti-wet-sanding zealots, who in their dusty halls grinded away in a powdery cloud that permeates everything it touches. Convinced that they were saving money by buying cheaper dry sand paper, they would actually use 5-10x the amount of sandpaper that wetsanding could have done in a fraction of the time, not to mention less physical grind on the body, and no dust.
Making the Case for Wet Sanding
Granted, wet sanding must be reserved for after the priming and sealing process. Dry sanding is a necessary evil during the metalworking and body filler stages, as moisture on bare metal and porous fillers can cause it’s own mess. But once the surface is sealed up, it’s time to get out the water bucket. Get a dedicated wetsanding bucket to prevent contaminants infecting the water. The bucket doesn’t need to contain water all the time, but when it does, it should only be for wet sanding. Contamination from grease or dirt at this stage can ruin the rest of the work, so the bucket shouldn’t have been used for oil changes or leftover mayo jars repurposed for storing bacon grease. Get a nice, clean, fresh bucket, sparkling with opportunity, and use it only for your wet sanding needs. Add a foam sanding block, and a small spray bottle of clean water for the fully equipped wet sanding kit. Crush any who try to corrupt the sanctity of your bucket.
A Drop’ll Do Ya
Beginners to wet sanding often struggle with the paper sticking or suctioning to the surface, fighting their efforts with every swipe. One simple trick that will save you so much frustration: a drop of baby shampoo. Just a single drop for a whole bucket of water. And yes it must be baby shampoo. The reason for this is that it breaks the surface tension of the water, allowing the paper to cut and glide on the surface, without dragging or suction. It also helps keep the grains on the paper clean and free from clogs, avoiding deep gouges that can be made by clogged sand paper. This is something that all soap does to water, but unlike most soaps, baby shampoo leaves behind no residue. It will rinse completely clean, where as soaps and shampoos often contain lotion or heavier residues. You will need to clean the surface with totally clean water after wetsanding, and the tiny amount of baby shampoo will easily rinse off. It’s also soft on hands, which you can’t say about much in this industry.
Sloppy Job: Slippery Side Effects
There are considerations to consider if you want to switch to wetsanding. The airborne dust you avoided by adding water is now a slimy slop that ends up all over your pants, shoes, and workspace floor. Care must be taken to clean up this mess once the work is completed, because its about the finest mud you could ever slip on. It’s worse than ice. A sturdy floor squeegee and mop will take care of this nicely.
Another disadvantage to wet sanding to think about is that you are going to get wet. Wet mucky sanding slop all over your hands and arms, on your belly from leaning to sand hard to reach places, all over your pants and soaking your shoes from constant drips. Proper footware is a must, as with all work done in the shop. Using warm water in your bucket makes thing slightly more comfortable, at least your hand will thank you. Dipping your hand into cold water for a few hours and you might not think dust is so bad after all.
Unmatched Quality of Finish
The real benefits of wetsanding are a smooth, even, clean, adhesion-promoting surface that when done correctly can produce far superior results in much less time, and although waterproof sandpaper is more expensive on the price tag, wet sanding uses much less sand paper because it cuts for so much longer. It stays sharp and usually free from clogs. If clogs occur during wetsanding, it’s usually because the primer or paint being sanded hasn’t cured completely (or in the case or really old paint that is decaying). For a more indepth guide to wetsanding where we cover techniques and which grit to use at every stage, see the full article on Wet Sanding Techniques.
Thorough Inspection and Surface Preparation Separates the Pros from the Cons
After being sanded, the piece needs to be cleaned and inspected as thoroughly as possible. The main surface should be inspected for any heavy scratches, chips in the primer, pinholes from body work, or any dings and dents that may have been missed by the bodyworker. Wiping the surface using a thin mild cleaning solvent on a lint free rag removes any last contaminants or debris. While this solvent is wet, the surface can be more deeply inspected by looking at the reflection of a light on the glossy wet surface. Long straight neon bulb lights are great for doing this, since the reflection is in a straight line and any deviation while you are looking over the surface will be glaringly obvious. Familiarizing yourself with Painting Prep Training and Techniques is part of the self discipline of becoming an expert painter.
Pinhole Pitfalls and What To Do About Them
What separates the professional from the amateur is not in getting it perfect on the first try, but knowing how to adapt to adverse situations. That being said, pinholes are a real nuisance. They are usually caused by bubbles that form in the body filler, which then get sanded partially through, forming a tiny crater on the surface of your piece. Although they are as the name suggests, small as a pin hole, they can hold moisture or contaminants and must be sprayed out with an air blower. Once clean, they must be filled because the solvent based paints will not bridge this gap, and will remain an open hole. Acrylic based spot putty is best suited for this task, it is solvent based and air dries without the need for primer (although it needs to be used only on the smallest of imperfections. anything bigger than a pinhole or a chip will require body filler putty, and again more primer). Allow this to dry completely, then wetsand with 400-600 grit paper.
Nooks and Crannies: Don’t Neglect the Crevices
Use a blower tip on an air hose to remove any left over moisture or sanding slop from the cracks around the edges of your piece. Anything left behind will create a loose barrier between the surface and your paint spray. This will eventually flake off, because the paint sits on top of filth and debris instead of making solid physical and chemical contact with the primer. Pressurized air combined with a cleaning solvent soaked rag gets rid of even the smallest amount of contaminants. These areas are seldom seen if at all, but these areas are also prone to collecting water and dirt, leading to rust. A good paint job covers every area of the piece, not just what is easily seen. As a professional painter, part of the creativity is figuring out which will be the best way to reach these challenging areas and achieve complete coverage. Indeed, planning this out is part of the inspection process.
You Can Never Be Too Clean or Careful in Automotive Painting
Painting requires a stable surface: any movement in the painted piece can lead to uneven coverage, or worse yet the piece could fall and cause chaos. Any combination of wires, hooks, or clamps can be utilized to secure the piece to a working surface, either a table or a painting stand. Certain pieces ought to be painted on one side only, then allowed to dry before painting the other side. Hoods, decklids, doors all come to mind, with the inside or underneath (unimportant, less or unseen) are painted first, and the important side painted last, this way the “bad” finished side touches whatever surface or fastening devices used to stabilize the piece. You can’t paint something that’s just flapping in the breeze, it needs to be secure and motionless to paint it correctly.
Removing any dust, dirt, or residue at this stage is especially important at this stage. Nothing can ever truly be perfect, but it’s good to try for 99%. Fingerprints, sweat, dust, crumbs, and residues can all stop paint from adhering, or cause it to bubble, wrinkle, or “fish-eye” (basically when the paint is repelled by an oily or silicone substance, it forms a little crater that resembles the eye of a fish, or so they say). Always err on the side of caution and give your piece one more wipe down with cleaning solvents. Silicone is by far the worst adverse reaction in paint, causing the fish eye effect more drastically than oil or grease. Get rid of/avoid any silicone products in your paint shop. They are very sticky and hard to clean off, and when you spray the paint it looks like the surface has leprosy. For this reason, many auto paint shops hang a bold sign forbidding silicone based products from the property.
Needles and Springs: Optimal Spray Gun Setup
Spray guns are truly a wonder of modern engineering, synthesizing artful creativity with industrial efficiency. What a good spray gun can do for your painting business can be summed up in one word: Production. Brushes and rollers have their place, but it’s not even a competition when compared to a trusty spraygun. While not exactly perfect, a quality spray gun can be fine tuned to lay on even coats of paint that are close enough to perfect to be made actually perfect later on when Detailing. Air pressure, paint volume, and fan shape are the three main setting to consider when setting up your spray gun for the automotive paint job at hand.
Finely Tuned Air Pressure for Smooth Coats
The air pressure setting on your spray gun regulates how much “push” comes when you squeeze the trigger. Most spray guns have a half-pull of the trigger, which pulls the needle far enough to release air, but not far enough to release paint. This is a useful feature as a last-minute blow off with clean air, or to blast away anything that fell onto the surface. This also stops the paint from spattering on the initial pull of the trigger, as any excess air pressure is released and allows an even air flow. A diaphragm regulator on a short pigtail air hose can give even more delicate air control, and are strongly recommended if you are using a normal air compressor. Air pressure in a spray gun is like bristles on a brush: its needs to be smooth and even. If its ragged and choppy, that’s how the paint will be too. Different paints will require adjustments in air pressure to go on evenly, although in most cases the air pressure needs to be pretty low. If it feels like you are holding a flamethrower, the air pressure is way too high. Too much air pressure also throws off wasteful and messy overspray, which can land on uncured paint and make it look dull. Overspray is unavoidable to an extent, but should be minimal. In almost every case, amateur painters have the air pressure turned up far too much, perhaps excited by the loud hiss and recoil, and the massive cloud of paint like some kind of mechanical dragon. Turn it down to a whisper and you’ll do much better paint.
Pump Up the Volume: Put Paint Where It Ain’t
Contrary to air pressure, the paint volume setting needs to be at the maximum comfortable setting. This of course will be different for each material, but as you work with a paint or primer enough to get a feel for it, you can accurately dial up the paint volume to get as much paint on the surface as you can without causing runs, drips, or sags in the paint. You want to get the paint on wet, with each pass putting fresh wet paint onto wet paint. It’s a delicate process, and paint can also act differently in hot or cold temperatures. In hotter climates, expect dry, clumpy overspray, especially at the edges of where you sprayed. When its colder, runs and drips are hard to avoid, in extreme cases resulting in a large section of paint oozing off the surface in something called a sag. Adaptability and situational awareness are tools you need in your box if you aspire to paint professionally. However, new painters tend to have too low of a paint volume, and are a bit shy about applying a thick coat, as well as moving too fast and leaving a thin, dry coat. Runs, drips, and sags are more of a sophomoric painting mistake: you have enough confidence to lay the paint on thick, but not enough finesse to avoid areas/conditions prone to drips. Between the two, it’s better to have a thick coat with a run than a thin coat thats dry. A run on thick paint can be sanded and buffed out, but a thin dry coat has less material to work with, with poor adhesion as a consequence. Dry coats will almost always need to be sanded and painted again.
Fan Adjustments Give You a Whole Brush Kit
Spray gun fan adjustment can be a double edged sword. It’s the feature that turns the sprayer into a dynamic tool capable of throwing paint in a pattern that spans from a point to a broad line. This enables fine tuning which allows the painter to spray an even coat of paint onto complex shapes. Inside corners and smaller areas such as door jambs are easier to cover with a tighter fan, where a wide fan cuts down on the number of passes per coat on larger panels like a hood or deck lid. This produces fewer edges, less overspray, and less arm fatigue. The tricky part is that with fan adjustments, you must also adjust the air pressure and paint volume. With a wider fan pattern, higher pressure and volume is necessary for a saturating coat, tuning them down accordingly as the fan pattern is narrowed. As far as common rookie mistakes with fan adjustment it would have to be ignoring it completely. Never using it, or maybe fiddling with it once and settling on somewhere in the middle. This is like having a whole kit full of different size paint brushes and using only one of them. Painting something like a car with complex, compound shapes and surfaces of almost every form, a professional painter needs to adapt to the terrain.
Method to the Madness: Automotive Painting Spray Application
Painting projects can include a myriad of different surface shapes, parent materials, and types of paint being sprayed. Add temperature and humidity into the mix and you can understand that painting conditions are constantly changing. There is one factor that remains unchanging no matter what you are painting: gravity. You can always rely on gravity to pull things downward. Because of this constant immutable force, the order in which you paint things matters a great deal.
Bottom’s Up: Why You Should Spray Paint Starting Low and Working Up
Start at the bottom and work your way up. This principle applies whenever you are spraying coats of paint, but is especially important in cars. When sprayed, the edges of the spray pattern can be “dry”, not necessarily bone dry but there is naturally less paint at the edge of the spray fan pattern. Gravity of course pulls this downward, and when using solvent based auto paints the dry edge and overspray will effectively melt into the wet coat below it. If sprayed top to bottom, the dryness and overspray is falling on dry primer, with the wet coat being applied over top of it, making the paint bumpy and uneven. This is why spraying paint must be done starting at the bottom and working upwards.
Running Against the Wind
Direction of airflow caused by the spray booth or ventilation system should be treated in the same way as gravity. The air should flow horizontally across the pieces, and painting should be started nearest to the intake fan. It behave like gravity, but sideways, and the same principle applies: better for edged and overspray to land on wet paint than onto the dry primer. Airflow usually has less of a pull than gravity, but it will still effect the way the paint lands, especially the overspray.
50/50 Overlap (unless otherwise noted)
Imagine the fan spray pattern is like the bristles of a brush. You want to paint side to side, starting at the bottom and close to the exhaust air flow, holding the spraygun about a 8 inches to a foot away from the panel, and evenly and steadily spraying from one end to the next, maintining the same distance and speed throughout. the trigger should be pulled enough to start releasing paint just before the spray pattern hits the panel, and released just after the pattern has passed the piece. This is why overspray is inevitable, and masking materials are needed. The edges must have the same amount of paint as the middle of the panels, and to achieve this you must paint beyond the edges of the piece. A helpful trick is to start by giving edges a light coat, particularly edges or small areas with complex shapes. this should be allowed to dry, then remove any dust or overspray with a tack rag. The main body of the panel can now be painted without worrying about hitting all the little spots of primer peaking through. That last coat is what really matters, so you want to paint all the difficult to reach areas first, then do the main areas with nice easy even coats of paint.
With each pass of the spray gun, you want 50% overlap with the last pass. An easy way to achieve this is to always aim the middle of the spray fan onto the top edge of the last pass. This ensures getting a good wet coat of paint onto that thinner, dryer top edge of the previous spray run. If you can imagine a coat of paint like a sheet of paper, you want to layer each successive “paper” so it covers half of the last one, and the next one will cover half of that, and so on.
There are exceptions to this rule depending on the type of paint material being sprayed. Waterborne paints come to mind, where it calls for a 75% overlap (doing this with solvent paints will lead to runs everywhere). More often than not, however, the 50/50 overlap rule applies to most primers, paints, and clear coats.
Single Stage Vs Base Coat: When to Use Each Type of Auto Paint
Automotive paint technology is perpetually changing and evolving, with new exciting products being released all the time. The chemical properties may change as far as which solvents and activators are needed, but top coat auto paint normally falls into two main categories: single stage or base coat. Each has it’s advantages, neither being better than the other, and is decided by either historical accuracy or simply stylistic decisions. The process for each type differs slightly, and you should understand the subtle nuances before choosing which type of paint.
Center Stage: Single Stage Automotive Paints
Single stage auto paint is formulated to be applied as the final top coat, without the need for a clear coat or sealer over top of it. These types of paint are much thicker and heavier-bodied than base coat, comparable in viscosity to many epoxy primers. For this reason, the volume needs to be adjusted accordingly on your spraygun to accommodate this thicker paint. Single stage paint goes on thick and heavy, it’s very important that you are getting wet coats and there is very little forgiveness with dry edges. If overspray or debris happens to get painted over, your only real choice is to pick it out and try to bury the mark under more paint, but this runs the risk of creating a run. Time between coats is another critical consideration, as painting a second coat too soon can lead to bubbles forming in the paint, something known as solvent pop. Solvent pop is caused by trapped solvents that get buried under paint, the top layer of paint forms a skin and doesn’t allow the deeper solvents to evaporate out, so they turn into little gas bubbles in the wet paint under the dry paint skin.
Due to its heavier formulation, single stage paint is incredibly durable. It is preferable for painting under hood and under carriage parts for this reason, and engine paints are almost exclusively single stage paints. When used as a top coat for the body of the car, they can be sanded and buffed to a glamorous shine, without the need for any additional clearcoat. Single stage urethane from Eastwood can produce a shine comparable to any clear coat on the market, but it will require the extra phase of sanding and buffing to achieve this.
Being able to paint in one shot, one spray gun, one clean up is a huge advantage to single stage. Combined with the generally lower price tag of a single stage paint, its more economical overall than a basecoat/clearcoat strategy without sacrificing quality or durability. In fact, in anecdotal experience, single stage paints stand the test of time better than anything, especially when you get into sign paints. When I see things I worked on 20 years ago today, single stage paint has held up better in every case and it’s not even close.
Based on Experience: Advantages of Basecoat
Basecoat as a color layer are the go-to choice when a clear top coat is the desired option. Base coat is a very thin paint, and acts almost like a colorant or stain for the primer rather than a layer unto itself. Because of this, sanding should be done to at least 600 grit, as basecoat is too thin to fill coarser scratches. Even something as fine as 400 grit scratch can flare up under base coat, especially when the base coat contains a metallic or pearlescent color. Basecoat is barely thicker than solvents, and cannot be relied upon to hide anything. The way to look at is is to consider how the primer layer looks, and that is how the final product will look. If there is any unevenness, heavy scratches, or small chips, the base coat won’t fix them, and will likely make it stand out much worse. Basecoat essentially “tints” the primer to your desired color, and dries to a very thin layer that must be clearcoated. Base coat alone has very little durability, and should be clear coated within hours of application. Using specialized paints can extend this window to about a week to allow for more complex designs and multi color paint schemes.
The major advantage of basecoat is that it requires less color paint to the same results as a single stage, and allows for metallic paint or intricate color designs to be sealed under a thick layer of clear top coat. Designs such as multi-tone or flames are mush easier to layer the colors and details using base coat, since it’s so thin it doesn’t build up enough to show up under the clear coat (rather it shouldn’t do that, if it does you used far too much base). Attempting these design using single stage paint are rife with problems, since the design paint will have to sit on top of the parent paint, requires more extensive masking, and can even wear off or flake away. Base coat also sets up much faster than single stage, with less time between coats. Multi tone color schemes using base coat are easier because each color can be sprayed onto the next, either “wet-on-wet” or after the short time it takes to set. Single stage would need to be allowed to dry completely, then sanded and prepped, in between each different color. This is acceptable for two or three tones maybe, but any kind of custom design quickly rules out single stage as an option and makes base coat the only way to go.
It should be noted that base coat dries to a dull matte finish. this is perfectly normal and in fact desired. The surface of the dried base coat layer becomes textured and creates more surface area for the clear coat to hold on to. Should a matte finish be desired using base coat, a flattening agent can be added later to the clear coat. Base coat must never be left without a clear coat for longer than it takes to get the clear on there, period. See our article about Applying Automotive Basecoat to learn more.
Some Like It Shiny: Clearcoat Shines and Protects
“You get what you pay for” is a phrase that rings particularly true when choosing a clear coat. While no single choice is the best, the rule follows that the more expensive the clear coat, the more durable it will be. All clear coats eventually start to break down due to UV exposure, turning yellow, then cloudy, then flaking off entirely. For some clears that takes 3 years, other clear coats won’t show signs of decay for 15-20 years or more. It’s no accident that the more durable clear coats are almost always more expensive.
There is a time and a place to save money, but your choice of clear coat should be the best your budget will allow. This is the final layer that will seal up and protect all of your hard work beneath it, and add a beautiful shine that can be sanded and buffed to perfection.
The Lowdown on Low Solids
Low solids clear, or Intercoat Clear, is a thin bodied urethane clear coat that is suitable, perhaps even necessary, depending on the application. In custom auto paint, this clear will serve as an intermediary layer between the basecoat and the top clear. It’s thinner viscosity allows for a metallic, pearlescent, or tinting pigments to be added without a lot of buildup. This layering effect creates a visual depth, compounded by the thicker layer of clear on top acting as a magnifying lens.
Low solids clear is also significantly cheaper than it’s higher solid counterparts, by virtue of containing less of these expensive clear solid elements of the paint. This also effects the durability of the clear: it will be thinner and less resistant to UV light exposure. This thinner buildup may be desirable in certain circumstances, such as adding a thin clear layer over and airbrushed mural (this acts as a “sealer” before the heavier topcoat clear is applied), or any piece that will be kept inside, away from the elements. Many airbrush artists opt for this type of clear as their go to choice due to the value and low build properties. See our full article about Airbrushing for more.
High Solids at High Noon
High solids clear, as you can guess, is a heavy bodied viscous urethane clearcoat, jam packed full of clear paint solids. This gives a thick top layer that covers, protects, and adds a hypnotic shine to your basecoat. These high end clearcoats slow the effects of degradation caused by sunlight, rain, and dirt, adding years of life to your paint. Spraying high solids clear *feels* closer to spraying a single stage paint, since it goes on thick, wet, and heavy. Care needs to be taken not to cause runs or sags in the clearcoat, but even seasoned pros get plenty of these (a good sand and buff can work wonders). The same application rules apply to clearcoat as single stage paint, but its more difficult to tell when you’ve gone too far and sprayed it on too wet. It’s clear after all. A tack rag should be used to thoroughly clean the entire surface, then wiped down with a mild cleaning solvent to remove any oils or contaminants that may have landed on the surface.
Clearcoating Pitfalls and How to Cope
A common and unavoidable downside to this high-build property is getting a paint defect known as orange peel. This is caused by air and paint molecules battering into the wet painted surface. This disruption dries with the paint, sometimes getting better as the paint cures and tightens up, but rarely does it disappear entirely. Particularly pronounced in high solid clearcoats, this phenomenon cannot be avoided, it is simply a factor you must try to minimize causing, and deal with it later. More pronounced, extreme orange peel will form when clearcoat was not applied wet enough in areas, covering up the dryer texture and compounding the problem with each pass. Unfortunately, a wet coat on top of a dry textured coat will not hide the problem and only make it larger. This is not to say you shouldn’t apply subsequent wet coats over top of such an area, the reality is that you already created the problem that you will need to fix later. In the picture, the lines indicate the edge of the light reflection, making orange peel easily visible. This is how you can check your own paint for this defect. The arrows indicate a couple of more drastic examples of orange peel, which is very common for an edge area like this. What separates the professional painter is being able to keep this to a minimum, making the buffing process less labor intensive. It really comes down to “just deal with it and take care of it later”.
Unintended inclusions can find their way into the clearcoat as well. The most common culprit is the painter themselves, dropping hair, sweat, lint, or dust onto the wet surface. With any paint, the painter needs to be clean and tidy, but this is especially important with the clear coat due to it’s finality. Dirt and dust can’t be buried under another coat, like with color coat, and with each layer of clear the problem actually gets magnified.
Bugs can also play a role in wrecking the clear. Never underestimate the ability of an insect to find their way into your fresh, wet paint. There seems to be something about the solvents that insects crave, and they will happily dive in and start swimming around, ruining the clearcoat before they perish and dry into the surface. Have a good set of picks handy to remove any unwanted trespassers in the wet clearcoat. This will leave behind a deformation in the paint, but at this stage of the game you just need to let it dry, and deal with it later. If it happened in the first coat, and you managed to remove it, you may get lucky and smooth it out with subsequent coats
A Pound of Cure: Curing and Drying of Fresh Auto Paint
Once the paint has been sprayed and dried, the curing process can begin. Even after the paint has dried enough to touch, the paint is still very much fresh and active. Solvents need a chance to thoroughly evaporate out, and the catalyzation of the paint to fully set, creating a durable bond. Infrared heaters are used as curing lamps to provide the heat necessary to facilitate this chemical process. Care and attention are critical when using a curing lamp, and are only necessary in colder temps. Nevertheless, the curing needs to happen whether it fits your schedule or not. At this stage, the paint can still be very soft in spots, and careless handling can easily mar the paint. The first two weeks after the application of paint, regardless of type, are very much the infancy of the paint. Room temperature of 65-75 degrees F in a well ventilated shop is the ideal range to allow paint to firm up and cure during this vital phase. Ideally, sanding and buffing to remove paint deformities should be postponed as long as possible, but this two week window should be the minimum. Full cure of automotive paint takes about 6 months, after which is the ideal time for addressing any issues. Patience goes a long way.
A Little Heat Goes a Long Way
Depending on your local climate, you may not need to equip your shop with a curing light at all. If you have sufficient heating and can maintain about a 70 degree temp in your curing room, regardless of weather, then you’re probably fine without further heating implements. There is a tendency for rapid production collision repair shops to heat up the paint and “bake” it on. While this does make the paint firm immediately, this causes a weaker bond in the paint itself. Additionally it can cause or exacerbate solvent pop, forming an impenetrable thick skin of hardened dry paint over a deeper layer of still-wet paint that needs to give off solvents. These solvent gas bubbles are made larger and more pronounced under a curing lamp, of course expanding as they heat up.
Less-reputable paint shops adjust to this by putting thinner coats of paint (dry and bumpy), furthering the overall crappiness of the finish. Bad habits layered on top of more bad habits lead to a lowering of quality, and a decreased lifespan of the paintjob. Extra heaters or curing lamps should be used as needed, rather than a standard procedure to expediate the curing process. See our in-depth article weighing the benefits of Air Drying Vs Baking Paint.
Don’t Make Me Blush: How to Prevent Blushing in Automotive Paint
Blushing occurs when things get too cold or damp, as the cold painted piece attracts moisture in the air. As the solvents evaporate, it cools the piece as it does so, attracting even more latent moisture floating in the air. Tiny water molecules form in the curing paint, creating a milky look. This can happen in single stage and basecoats or even primer, but like every other paint hazard is most evident in clearcoats. Depending on the depth and extent of the blushing, it may need to be sanded and painted again. Buffing can get it out if it’s only a surface blush, but if the water vapor has penetrated too deep into the paint, you’re going to need to repaint it. Moderate heat, air flow, and in extreme humidity air dryers can help prevent blushing and allow paint to cure correctly.
When Mars Attacks: How to avoid Marring and Deforming Fresh Auto Paint
It feels dry to your hands, but the paint is still soft. Careful handling is of utmost importance at this point. The material is on the piece, and any damage at this point would send you multiple steps backward. Fingerprints can easily be pressed into the soft surface of the paint for weeks after it has dried to the touch. Smaller shops need to reassemble uncured parts to save on room (it takes up less space on the car than on a parts stand), if this is your situation you must be extra careful when doing this. Fastening the part with bolts, clips, or screws will definitely tear and deform the soft paint, so only pin them on with a few fasteners just to hang it in place. Tighten it the rest of the way once the paint has actually hardened.
Avoid adding any type of polish at any point during the curing process. Not only is it not going to do anything beyond giving the paint a “wet” appearance, it can also cause the paint to get dull. This is because residues from the polish become embedded into the outer surface of the paint, creating a cloudy effect sometimes called “hazing”. Not as severe as blushing, but the paint never looks as good as if it were left alone. Hazing in paint has a chalky and slightly greasy feel. Luckily this can be sanded and buffed to a perfect shine, the correct way. The final sanded and buffed surface is then ready for polishing, since the perfectly sheer surface lets the polish sit on top but doesn’t absorb it like when it is still soft.
Explore Deeper
Automotive painting can be a highly profitable endeavor when approached with professionalism and know-how. This aritcle aims to provide an overview of the custom auto paint process overall. Each project that rolls into your shop will be unique in it’s own way, but universal principles can be applied to paint anything. Further specific topics will be explored, each focusing on particular situation. Hopefully you have a general idea of what you would be taking on when considering auto painting as a business. Please enjoy our other articles where we get into related paint tips and tricks that can be incorporated into an automotive paintjob. If a video teaching guide is more your flavor, check out my earnest review of Spray Paint Secrets for Transforming Automotive Passion into Professional Excellence.
Source: Autobody 101 Forum