by Pat Ganahl
(Taken from How to Paint Your Car on a Budget by Pat Ganahl)
The only way to learn how to spray paint is to do it. Practice. Make runs and drips. Make orange peel. Make fisheyes. Keep practicing until you start to get a feel for the spraying process: how close or far away to hold the sprayer; how to move your hand to make even passes; how much to overlap; where to start and stop; how much paint to put on to make it smooth (without orange peel or dry spray), without letting it run or sag. You can practice with your spray gun and compressor, but I strongly suggest you start with spray cans. It’s quicker and cheaper. Start small and work your way up. I mean literally small. I started with model cars and bicycle frames. Those are the kinds of things spray cans are made to paint. You won’t learn much trying to paint big garbage cans with spray bombs; stick to things more the size of buckets. Or skinny things like wrought iron fences or chairs with rungs.
The first step is to clean the object (soap and water, wax and grease remover, or even cheap lacquer thinner on a rag). This should eliminate fisheye or separation problems. Second, sand the object to get rid of any scale, cracks, and crud, or just to scuff up the surface for adhesion. Paint doesn’t adhere to a slick, shiny surface.
One of the best “tricks” to learn with spray cans is to start with a light, quick, dust coat. Don’t try to put a layer of color on the surface with your first application. Move the can quickly, and waft it back and forth in several directions, just enough to get a very light, even, slightly sticky coat of paint all over it. This is what’s called a “tack coat.” Let this dry for about five minutes. Then spray your first color coat over this. Keep it thin, and spray in smooth, long passes, overlapping each pass about 50% as you move from left-to-right, then right-to-left, but make this coat cover the object in color—just enough color to cover it. Let this dry 10 to 15 minutes, then spray another smooth, thin color coat. When it looks like the object is fully and evenly covered in the new color, after waiting another 15 minutes or so, make another pass, moving your hand a bit slower so you spray more paint (but not too much!), hopefully producing a smooth and glossy surface. This is, of course, called the “gloss coat.” If the first full pass around the object being painted doesn’t look shiny or smooth enough, try going around it once more, right away. This is where you learn to spray paint. Unfortunately the type of paint in the can (and other things, like the weather) affects it. But it either gets smooth and glossy, or it gets runs. Keep practicing until you get it smooth and glossy.
Turning the fan control knob in (clockwise) reduces the width of the fan pattern for spraying smaller areas. When you do this, you should also reduce the fluid flow rate by turning in the second knob down (on this gun), plus reduce air pressure slightly with the knob where the hose connects to the gun.
Most of the time you are spraying with the fan and fluid control adjusted wide open, and the nozzle turned so the fan sprays vertically, as shown.
Mixing and “Adjusting” the Paint
Okay, let’s move to the real stuff. Virtually all automotive paints, new and old, require thinning with what we now call “reducers” to make them the correct consistency for spraying. This is done for several reasons, beginning with the fact that it’s easier to store and mix paint colors in smaller amounts. But the real reason for adding the reducer at the time of painting is to allow the painter to adjust not only the consistency of the paint, but also its drying rate, to match his own spraying preferences and weather conditions, specifically temperature. So automotive paint, itself, is “adjustable” in two ways: you can control its viscosity (how thick it is), and how quickly it dries. In the old days of straight enamels and lacquers, thinning allowed much more flexibility. The recommended reduction might be anywhere from one to two parts thinner to one part paint, and thinners came in at least fast, medium, and slow speeds. These variables affected only the paint’s spraying viscosity and its drying rate, not how it “cured” or its long-term stability. The rule of thumb was that you didn’t want the paint too thick—you wanted it to “lay out” rather than orange peel; and in most climates, especially with lacquer, you didn’t want the paint to dry too fast, because that would lead to a condition called “dry spray,” which is a pebbly overspray on the surface. Painters who had to work in cold weather in non-heated shops needed to speed up drying times.
Who knows what the paint variables might be in the future when we get water-based or other types of paints perfected? But for now, with catalyzed paints, things are much more stringent than they used to be when it comes to mixing paints and their various additives. Some materials—certain sealers, primers, and clears—take no reducer at all. Add exactly the amount of catalyst, sometimes called “hardener,” specified, and spray it. Several other types of paints—mostly base coat colors these days—use what’s called a “reactive reducer,” which has the chemical catalyzing agent in it. These should generally be mixed in the exact proportions specified, so you can’t adjust viscosity much, but the reducers do come in different temperature ranges, usually denoted by the number on the can. For instance, PPG DRR-1185 is a reactive reducer (RR) meant to be sprayed in an 85-degree environment. If you find your paint drying too quickly, switch to a higher-number reducer, say 1195, which dries slower (the opposite, of course, pertains as well).
One important note: I don’t know the chemical specifics, but these reactive reducers have a short shelf life once they’re opened to air. Within a week or so, they go bad, and there is no way to test them or tell this, until you mix and spray some paint and it comes out splotchy and weird. Hopefully, in time, they’ll improve on this.
A third type of current paint takes a specific, small amount of catalyst, and a reducer, which not only comes in different temperature ranges but can also be increased or decreased within limits to “adjust” paint viscosity. Again, unless you’re painting in really cold weather (which is not generally advised, anyway), the rule of thumb—if your paint is “adjustable”—is to mix it a bit on the slower and thinner side, rather than vice versa.
Adjusting the Gun
Excluding pressure pots, which we’re not considering, every type of automotive spray gun—siphon-feed, gravity-feed, HVLP, non-HVLP, touch-up, whatever—has three adjustments: air pressure, fan control, and fluid control. Most HVLP guns have an air pressure valve, and dial gauge, attached to the gun. Other types don’t, but we strongly advise you add one, with or without a gauge, where the air hose attaches to the gun. It’s air pressure at the gun that counts, and needs to be controlled steadily. The fan control knob on the gun widens or
narrows the paint fan pattern, so the paint covers a larger or smaller area as you paint. Note that the gun’s nozzle
or spray tip can be loosened and turned for a vertical or horizontal fan. Most automotive painting is done with a wide fan in the vertical spray position, as you move the gun horizontally—left and right—while painting the body of the car. Certain smaller areas are easier to paint with the fan adjusted narrower, and vertical areas (such as doorjambs) where you’re moving the gun up and down, are easiest to paint with the tip turned to a horizontal fan.
Most automotive painting is done with the fan and fluid controls wide open and the pressure set to what is compatible with the type of paint and type of gun you’re using. When you narrow the fan pattern, you are still spraying the same amount of paint in a smaller area, and its velocity increases. That’s what the fluid control is for: when you decrease the fan width, decrease the paint flow proportionally with the fluid control knob, so it covers properly without running. You do this by feel and experience. Likewise, you usually want to decrease the air pressure in the same manner, for the same reasons. That’s really all there is to gun adjustment. However, if you’re resetting adjustments on your gun, it’s best to test it on something other than your car, to see if you’ve got it right. I use the side of a trash can.
When using the wide, vertical fan pattern, you should hold the gun parallel to the surface as you spray. It’s not as easy as it looks, especially in the middle of a roof. Keep a step stool handy, if necessary. This example is close, but not quite right as the bottom of the cup is too close—the gun is not parallel.
On the other hand, you can’t adjust a spray gun if it’s not working properly. If the gun sprays more paint at the outer ends of the fan than in the middle or vice versa, or if it “spits” while you’re spraying or sprays unevenly in any other way, you need to clean, fix, or replace the gun. This assumes that your air compressor is 1) functioning properly; 2) big enough to keep up with your gun, and 3) designed for an HVLP gun, if that’s what you’re using. Thoroughly clean every gun after each use by spraying lots of cheap hardware-store lacquer thinner through it and wiping it dry. Do not use sharp objects, such as wire, to clean the gun. And periodically add a few drops of light oil to (or replace) the packing around the needle so it doesn’t leak air. A good gun that gets worn can be rebuilt; cheap ones can be replaced.
Once you’ve got the paint mixed properly, and the gun adjusted, the only magic left to painting is the motion and operation of the gun. This, as we’ve said repeatedly, requires practice to develop the proper “feel” for spray painting. But the basic pointers are simple.
For most types of paint, hold the nozzle about eight inches (an outstretched hand-width) from the surface at all times—when making a pass, do not swing the gun in an arc. Most painters spray panels that are a full arm’s width at a time, top to bottom, then step to the next panel, and repeat. If you need to step side-to-side as you’re painting a wide panel, to keep the nozzle the same distance from the surface at all times, do so. Pull the trigger to start spraying paint as you begin the pass, and let go to stop spraying at the end of the pass. Then move halfway down the spray pattern, and start your pass back, pulling the trigger as you begin to move your hand the opposite direction. Do not pull the gun away, or move it down, while still spraying.
When spraying, keep the gun the same distance from the surface at all times. The old rule was a hand’s-width (6 to 8 inches) away, but painters using HVLP guns tend to hold it closer, which makes sense because the pressure is lower. In any case, holding the gun too close causes runs; holding it too far away causes orange peel or, worse, a rough, “pebbly” surface. Too much or too little air pressure and fluid flow produces the same problems.
Keep the gun nozzle perpindicular to the surface at all times, whether you’re spraying the roof, side, or in a wheelwell lip. Many painters are careless about this, and it leads to uneven coats.
Not only do you need to keep the gun parallel to the surface (viewed from the side) as you spray, but you also need to keep it perpendicular to it, as viewed from the top.
In other words, keep the gun the same distance from the surface throughout a full pass from side-to-side. Do not swing it in an arc, so that it’s angled to the surface at the ends of the pass, like this.
Finally, most painters like to start painting at the top of the vehicle (i.e., roof) and work down, in a rotational pattern. This is so any overspray that falls on the surface gets painted over (and hopefully melted in), rather than falling on top of fresh paint. For similar reasons, you want to paint panels consecutively around the car, so that you are overlapping the wettest paint with new wet paint, allowing it to blend together. Most painters spray, for instance, the whole top, then the hood, then the left side, then the trunk, then the right side.
Your goal is to get an even color coat on the vehicle, without streaks, splotches, or darker areas where paint overlaps. Of secondary importance is minimizing dry overspray at the edges of panels. This is more important with clear coats or color gloss coats that won’t be cleared. It’s extremely important if you don’t intend to rub out the finish. The trick is to spray your final gloss coat (color or clear) quickly and fairly heavily, so that it all stays wet from start to finish. This is easier said than done.
One last general rule of spray painting: the days of “40 hand-rubbed coats” are long gone, and were bad to begin with. Paint and metal have different coefficients of expansion, and cars are subjected to wide variations in temperature, especially going from the garage to the open, hot sun and back. You want the minimum amount of paint (including primers, etc.) on the car as possible. You must put on enough color to cover properly. And you’ve got to spray enough clear or color to allow for color-sanding and rub out without fear of rubbing through—and even, preferably, allowing for a second rub out later—if you’re going to rub it out. But adding thick, multiple layers of paint (or primer, without sanding most of it back off), only leads to cracking, splitting, and checking as the paint ages and is subjected to the elements.