david's blog

“Foursquare” is the best word to use in describing how a spray gun should be held relative to the surface that you are currently painting – any deviation of angle is likely to cause faults in the finished paint, possible ones that are large enough to merit stripping and starting over again. Although the human hand is not an absolutely precise instrument, and spray gun techniques are robust enough to accept a little “wobble” in the angle, you should try to maintain correct positioning as accurately as possible throughout the paint job.

Generally speaking, a painter cannot go wrong by laying down each stroke of car paint with half of its width overlapping onto the stroke immediately before it. This ensures that there is an even, thorough coverage, with excellent blending between the strokes so that there will not be horizontal stripes visible on the car’s surface like those found on a childhood magic marker drawing.

A complex combination of air pressure, paint viscosity, surface preparation, painting speed, positioning of the spray gun relative to the surface, and the painter’s gait and steadiness of hand are all involved in producing a smooth, even, glistening paint job when the car is finally rolled triumphantly out of the garage or spray booth. However, all these other factors are rendered completely null and void if one particular detail is not attended to – the need to overlap your strokes.

Even if you have no problems with your spray pattern – such as a bulging center-heavy pattern, the peanut shape of a split pattern, or the cashew-like curve of a blocked wing port – then you will need to adjust the width of the pattern to match the materials you are using and the job you are undertaking.

Since drenching the exterior of a car in a single, simultaneous, smoothly even coat of paint is impossible, it is necessary to paint a vehicle in swathes several inches wide, known technically as strokes. Strokes can be made either horizontally or vertically – horizontal strokes are much more common, and are used for most painting situations, but there are some occasions when a vertical stroke is necessary. The spray gun must be adjusted to each of these situations, which is fortunately a fairly simple operation.

However, there are some painting experts who argue eloquently in favor of using a second spray gun for nothing but primer – and, as with their opponents who hold that “primer guns” are an unnecessary expense, they base their argument on the considerable expense of a new spray gun.

The cost of a good spray gun is not negligible – at around $350 to $400 apiece, they cost as much as lower end personal or notebook computers – so the question naturally arises whether it is necessary to buy a spray gun for primers and another for paint and finishes.

Although some solvent may be too badly contaminated by paint to be used again – depending on the type of paint involved and other considerations. However, much solvent can be salvaged, especially after the initial cleaning spray through the system – the following rinses, though essential, are likely to be far less tainted than the first load of solvent, and even if that needs to be disposed of. You will not want to use this “recovered” solvent for any other purpose than cleaning in the future, however.

Since a spray gun needs to be cleaned after every use – sometimes within a half-hour or slightly less, if permanent crosslinking between paint remnants and catalyst will occur within that time, causing an immovable plug that no amount of solvent or soaking will remove – it soon becomes clear to anyone who makes regular use of a spray gun in car painting that a lot of solvent is going to be used in the cleanup process. The amount of solvent needed is increased by the fact that much of the troubleshooting needed for a spray gun involves cleaning different parts.

Some materials problems are even more serious than those which were just described; these hindrances can prevent the paint gun from working at all until they are addressed, or cause such huge flaws in the paint application that the spray gun might as well be non-functional.