Here Brian demonstrates good painting technique with the gun
perpendicular to the surface.
Learning to get the paint from a gun onto a surface without it sagging, running or being too dry is not a skill, it is an art and an art that can only be perfected by practice, practice, practice. Even after numerous practice sessions you still may not be able to acquire the touch. Your first paint job will not be a pretty sight, and your second or third jobs probably won’t be award winners, either. If you stick with it, you’ll probably get very good at buffing, because you’ll have a lot of imperfections to try to fix. But stick with it. Remember that the early cars had their paint applied by brush and were sanded and rubbed out, so it can be done.
Spraying can be practiced on odd shapes such as bicycle frames and tool boxes — almost anything in your shop or garage that needs a new coat of paint. Paint anything that gives you spray time and an opportunity to work on your skills. Once the word is out that you are a painter, all your friends will want you to do a spot job of complete paint job for them. After you do a couple of nice paint jobs, there will be no shortage or work coming in for you to practice on. Oh yeah, and make them buy the paint.
Equipment is obviously a key component in paint work and you will want have a good-quality gun to shoot a good-quality paint job in a timely manner. That is not to say you can’t get good results with an inexpensive gun, but it will take longer if you figure in the time it takes to fix a few runs and rub out a few dry spots. So the gun issue boils down to simple economics: What you save on a gun will cost you in quality and extra time. Heck, you could paint with a brush and then spend many, many hours sanding and rubbing the paint to a flawless finish and not have spent a dime on a gun. Or, you could buy a good quality gun, take the time to learn how to use it well, then spray a coat or paint that is good the first time and does not need hours of sanding, rubbing and touch-up.
There are all kinds of gadgets that will spray paint. There are pressure pots, gravity-feed guns, siphon guns, low- and high-pressure guns, big guns, small guns down and many different varieties of air brushes. What we will focus on here is the HVLP Gravity Spray gun. The HVLP just stands for “High Volume Low Pressure.” The HVLP gun has gained popularity in the last 20 some years and was designed to keep the majority of the paint on the car and not in the air while utilizing the least amount of air to perform this task. In the beginning there was quite a learning curve as we all grumbled and complained about the guns and how we liked the old ones that really put out the paint. Well, the gun manufacturers listened and kept redesigning the guns to the point that they are today, and either they are better now, or we finally learned how to use them. Today, you can now lay down a pretty decent paint job with only 10 to 20 psi, something unheard of 20-some years ago.
We jam and paint the edges first as we go around a car, allowing the
paint in these areas to set up a bit before painting the larger flat
areas. This gives us a chance to control the paint in the hard-to-reach
areas first, then get into the simpler flatter areas last.
|A fly found a way into my booth and this is where he decided to land. Keep a set of tweezers handy for just such an unwanted guest.|
Handling the Gun
The typical spray gun has a few knobs that can be turned in or out to increase or decrease this or that, giving the painter an unlimited number of options over air pressure, paint volume, flow, ratio of paint to air and amount of trigger pull. Some of the guns, like the SATA, are even digital (as far as the air pressure is concerned). Guns are made from aluminum, magnesium and even plastic, but most of the designs are basically the same. Control of the paint flow does not stop at the gun. You will also have controls at the air compressor and water traps as well as pipes and elbows along the way. Just one 90-degree elbow will affect the final pressure a small amount, so if you have a bunch of them in the line along the way, it could make a huge difference in the gun’s performance. Don’t work with old hoses, either. I have seen a flap of rubber on the inside of a hose block the air supply and cause a few painters to scratch their heads.
If you look at the typical spray gun, you will notice the highest and most rearward portion of the gun has a small knob that can be turned in or out. This controls the spray pattern. The pattern can go from an elongated oval to a round pattern and back by simply turning the knob.
Brian has found a small run and a spot of dust that will be magnified if it’s
painted over. In this instance, he block sanded it down flat and smooth and
later re-sprayed the white base.
Candy is not an easy color to paint. It is transparent, and any imperfection
in the base coat is easy to see.
Below that is a fluid control knob that controls the amount of paint that exits the nozzle by determining the amount of trigger pull you have — the further you pull the trigger, the more fluid you get out the nozzle. It is really just a way of mechanically stopping you from pulling the trigger too far.
Now if you look down near the bottom of the handle where the air line hooks up, you should (better) have an air pressure regulator with a knob to control the amount of air pressure you have coming into the gun. Many states limit this amount of air pressure to 10 psi (over this pressure I guess they assume air kills people, or something), so start with 10 psi. Once you have paint in the gun, pull the trigger slowly as you slowly turn the air regulator in. What you are looking for is how low you can get the incoming air pressure and still achieve full atomization of the paint. This will be the air pressure setting to use for that type of paint.
It may all seem simple, but between the three controls you have many different settings. Pay attention and make notes on the settings so you can keep things straight as you switch brands and types of paint. Remember, most of the paint companies print the desired setting on the can or in the paperwork that accompanies that product.
Patterns are the consequences of the settings: good settings = good patterns, bad settings = bad patterns, and patterns are what make a good paint job. A good pattern is elongated and even and consistent, laying down the proper thickness of paint throughout the entire pattern. Not more on one end or the other, but the same thickness through the full length of the pattern. A well-designed spray gun operates somewhat like a carburetor that is set to get the perfect atomization for the perfect burn. Unless you really know what you are doing, don’t start re-drilling your gun’s nozzle to get more paint out of the gun. The manufacturers have different nozzles available for different paints. Check with them if you need a special tip for a special job.
Spray patterns can be changed and I often do change them, depending on what I am painting. I may bring the fan width down (turning the top knob inward) for a bike frame so I do not waste paint, but this means I am putting out much more paint in that smaller area, so I will have to cut down so I will turn my control knob in a few turns to limit the paint volume.
I also rotate my tip (cap of the gun) when I paint a vertical surface such as the A, B or C pillars of the cars. I don’t like to tilt my gun when I paint, I would rather rotate the tip or cap instead of the whole gun. When spraying a typical pattern down the side of the car you will need to start at the top and spray a single pattern down the side of the car with the middle of the spray pattern at the top edge of the car’s top edge. This way, when you overlap the next successive pattern you will wind up with exactly two coats on the entire side of the car. If you would start with the top of the first spray pattern at the top of the car and proceed to overlap the next coat 50 percent of the first pattern and each pattern after that, your first spray pattern would only have a single coat at the top 50 percent and double coats the rest of the way down the side of the car.
The most important aspect of spraying technique is to be able to see the paint lay down as you spray. If you can’t see how the particles atomize and lay down, it’s like shooting in the dark. Learn to read the paint and get used to the look and feel of the paint as it hits the car’s surface. Does it look dry or runny? Is it shiny, or dull and flat looking? Does it look constant from one panel to the next, or is it different from one to the next? Can you tell where you started the pattern and where you stopped, or is the paint seamless as it should be?
|While spraying a base coat you’ll often find small spots that will need repair.|
We sometimes have to block sand the area down again, allowing us one last chance to get the finish perfect.
You will only learn by doing. No amount of reading will give you the feel, and you will only learn by making mistakes. When I was starting out, I had no training and had to learn on the cheap using a gun with a small clunky compressor without a filter system. I learned in a hurry how to diagnose and repair paint mistakes. I could spot a problem before it happened, but could do little to prevent it. Now, of course, we have the best equipment and a few years under our belts, but still have some problems as we switch brands from time to time. I still, on occasion, see the look of panic on Brian’s face when a particular paint he is using doesn’t react the same as a previous paint did with the same pressure and conditions. He always gets a handle on it and finishes the job, and when I ask him “How did it go with the new paint?” he always answers “Great, no problem!” Yeah, sure. Even the experts have problems, they just have the experience to overcome them.
|Rubber sanding blocks for color sanding are pretty much necessity items. You will get a few runs in the beginning and have to sand them out. During wet sanding, they are the best tool to form the sandpaper around.|
Proper HVLP gun technique is the last thing on most new painter’s minds, but it’s the most important thing to learn in the beginning, something that takes a lot of practice to master. Ideally, you want to keep the gun 6 inches from the surface of what you are spraying, and the gun must stay perpendicular to the entire surface as you move it along at a consistent rate of travel. Now, this may sound simple, but try it — it’s tougher than it sounds. Combine this with the gun having to be shut off at the end of each stroke and started up (pulling the trigger) as the stroke reverses back down the panel, and you’ll find there is some real coordination involved.
I have found that the best way to practice is to go very slowly with an empty gun and just air paint a car to get the feel of the gun and the motion. Every so often stop and measure how far off the surface you are. If you almost touch the surface with the nozzle of the gun, you would have created some major runs. It shouldn’t take long to get the idea and soon you will be ready to load up a gun and try it with paint. I like to practice on odd-shaped objects such as tubing, and things that are round, such as barrels. Practicing on a flat surface is pretty easy. Practicing on a curved surface will accelerate the learning curve.
Many painters will tell you that performing a spot repair is more difficult than spraying a complete car. While a complete job may involve more labor, there are certain aspects of spot painting that can only be fully appreciated by an experienced refinisher.
Painting a complete car is certainly not without its share of potential pitfalls and problems but, for the most part, these are predictable and easier to avoid than those associated with spot painting. Unfortunately, the variables of spot painting are so numerous that we couldn’t possibly cover every situation in detail. However, once you understand the basic procedures involved with spot painting, you’ll be more able to handle whatever job might come your way.
This illustration provides an example of how the individual layers of material are applied in a spot
repair. Inexperienced painters often end up painting the whole side of a car because they can’t get
the right blend. As with all paint processes, practice makes perfect.
An easy spot repair usually consists of repainting a solid non-metallic color on a late-model car. A solid color on a late-model car can usually be matched with accuracy, or can be purchased as a “factory pack” premix. Another easy spot repair is a panel that must be repainted. A valance, front fender or any section of a car that can be masked off separately from the remaining car body eliminates the need for blending. The blend of a spot repair and the match of the color are the two critical factors of a spot repair.
Certain colors are more difficult to match than others and as you gain more experience with different types of repairs, you’ll find out what colors are hard to match and which ones are easy. I’ve found that metallics in general are always more difficult to match than solids because the variables are greater. Not only are there more toners in the formula that the paint mixer must accurately measure, but the application of a metallic involves making sure that the paint particles lay down exactly like the existing paint does. This means that your spraying technique and air pressure at the gun are extremely critical. For example, a lower pressure tends to darken a metallic, while a higher pressure lightens the tone.
In the accompanying illustration, you can see the left rear quarter panel of a car. The rear quarter panel almost always involves blending, due to the fact that there is no clean break-off point where it can be masked off. Most quarter panels are part of the pillar and roof section of a car, unless it is a convertible model. So, if a very small area of a quarter-panel must be repainted, the goal should be to confine the repair to the smallest area possible without having to paint additional sections of the car unnecessarily.
Now the fun begins. The entire car has to be color sanded with fine wet or dry
Perhaps the easiest way to describe how to perform a spot repair with minimal confusion is that each coat of material is applied in overlapping layers. This begins with the repair itself. Because paint must be spotted in, it is important to keep the working area of the repair to a minimum. Allowing your bodywork to spread out will increase the area that must be repainted. Keep in mind that painting all the way up to the edge of a panel will require an absolutely perfect color match. The objective is to avoid this by allowing yourself a large blending area to compensate for any minor differences between the new paint and the existing finish. For a small dent in a quarter panel, you would perform the dent repair followed by the primer coats and block sanding, again making sure to keep your work area to a minimum. When the area is ready to begin painting, you can then apply the color until full coverage is achieved, then you can gradually blend the paint application away from the repair and into the existing paint. Once the color is successfully applied, you can add the clearcoat if necessary, followed by a blending solvent to cut the dry spray at the blend. Once it’s cured, you can buff and glaze as normal.
Once we got the car in the booth, this job went well. The process took about a gallon of paint and
two gallons of clear. Brian did not go for the ‘high shine’ finish in the booth, as he knew that would
risk a potential run in the paint and the car was going to be buffed out completely anyway.
The Nitty-gritty of Sandpaper
What is the meaning of grit when it pertains to sandpaper, Grasshopper? An old wiseman once asked, so Grasshopper looked it up on the Internet and, being the smart grasshopper he was, he not only found the answer within minutes, but found the answer to be wrong! (True, the Internet is only as accurate as the input of the dumbest donor). The Sandpaper 101 Web site (yes, there is a Web site on sandpaper) stated that the grit is measure by “how many grains of sand will fit into a 1 inch square.” What it should have said is the number of grains of sand that fit on a 1-inch line, not in a 1 inch square. Let me explain: If you lay down large grains of sand on a line that is one inch long there would be, more or less, 16 grains of sand for 16 grit paper if you filled a 1-inch square with these large grains of sand you would have about 256 grains of sand. Further, if you laid down 3,000 grains of sand on a line for 3,000-grit sandpaper and then filled a square with the small grains of sand you would have 9,000,000 grains of sand in 1-square inch of sandpaper. Have you ever heard of 9-million grit paper?
Sandpaper grit is a linear measurement, not an area measurement. If you doubt me, go out and measure your sandpaper grains, but start with the 3,000-grit paper — anyone can measure the 16-grit paper. Report back to me next year.
Sandpaper is rated as follows:
36-grit is considered coarse-grit paper and is used for removing dead birds and stripping paint form the surface of a car. It can be used during bodywork to rough out the body filler after using a grinder or cheese grader.
80-120-grit is called medium-grit paper and is the next stage in removing the scratches that were put in by the 40-60 grit paper. This paper will start giving you the shape for the finish panel.
180-grit is used before the first coat of primer. Primer will fill in the scratches from 180.
280-320 grit is considered extra fine and is normally a “wet or dry” paper, but should only be used wet. This is used to take the initial primer down for the second coat of primer.
360-600 grit is be used just before the base coat is applied. This will be your last chance to catch any imperfections in the paint.
|Color sanding will take a whole day, if you are lucky, and will wear your fingerprints off. We add a bit of soap to the water to keep the sandpaper from sticking. Many shops use 1,500-grit paper for color sanding.|
Editor’s Note: Please be aware that sanding and spray painting should be undertaken with great care for personal safety and protection of the environment. Today’s paints, primers and fillers can be very dangerous, even deadly. Always wear a respirator and proper skin protection to avoid contact. When possible, rent a spray booth and the necessary equipment to get the job done safely.