Using a spray gun to apply paint can be quicker and easier than other methods and can give a better finish. Some paints – car body finishes, for example – are specially formulated for spraying; other paints can be sprayed provided that they are “thinned” with solvent.
Successful spraying requires a fair degree of skill and knowledge both about the paint you’re applying and the paint spraying equipment itself.
There are two main types of spray gun: with separate compressors or airless.
Spray Guns with Separate Compressors
These are the conventional design of spray gun. Originally, they had large compressors plus a bulky ‘receiver’ to balance out fluctuations in pressure. This type of equipment can still be bought (or hired), but the amateur is more likely to be interested in one of the range of smaller guns with separate compressors. The compressor, which is electrically powered, provides a supply of air under pressure to the gun which has a container for the paint.
Some of the air passes into the paint container to pressurize the paint; the remainder comes out through the nozzle as a fine stream. When the gun’s trigger is pulled back, a needle valve at the back of the nozzle is opened and the paint passes up from the container past the needle and into the air flow. The paint mixes with the air flow to provide a fine spray from the nozzle. The amount of paint that flows can be controlled by the trigger the further that the trigger is pulled back, the more paint that flows – though in practice the amount is limited by the power of the compressor.
Airless Spray Guns
These have all their working parts within the gun unit and have no separate compressor. The paint is forced directly out of the gun by a piston which vibrates backwards and forwards, being driven by an electric armature. It requires a considerable pressure to force the paint out of the nozzle and the amount of paint can be varied by adjusting a knob which alters the length of the piston stroke, though this is generally a fiddly operation. Obtaining a very line spray on an airless gun is difficult since the paint has to be pressurized to a certain level to gel any spray at all.
Airless guns are more compact and cheaper than separate compressor guns, but they do have disadvantages:
– The vibration of the piston can make it noisy and uncomfortable to hold
– An airless gun can ‘splutter’ paint when the level in the container is low. This should ruin a nearly completed job and it is not particularly easy to sec when the paint containers are getting empty. (When spray guns with separate compressors gel empty, they simply produce I spray with less and less paint)
– Because the paint can come out of a gun at extremely high pressure, there is a danger of ‘injecting’ the skin with paint if you put a finger too close to the nozzle. This is a serious injury as the paint can spread out under the skin. It is difficult to treat, but requires immediate medical treatment it is important to explain to the person who is treating you exactly what has happened. Most high-pressure airless guns have safety cages round the nozzle to prevent this happening.
For bodywork repairs on cars, small aerosol spray paint cans are available. These are used in much the same way as spray gun for car painting. Both primers and topcoats are available – it is important to know exactly what color shade your car is. Although convenient to use, aerosol sprays are an expensive way of covering anything other than small areas.