High-quality car painting is the highest aerobatics in body repair, where the result depends 90% on the skill of the master and 10% on the correct selection of equipment. Usage spray gun allows you to create a perfectly smooth glossy layer, free of shagreen and drips, which is almost impossible to do with an aerosol can. However, to achieve factory quality, it is necessary not only to buy a good tool, but also to thoroughly understand the physics of the spraying process, torch settings and material viscosity.
Beginners often make the fatal mistake of thinking that simply pulling the trigger and moving your hand is enough. In fact, working with pneumatic sprayer requires synchronization of movements, control of distance and understanding of how paint behaves under different air pressure parameters. In this article we will analyze the entire cycle: from setting up the compressor to the final pass of varnish, so that you can avoid defects and waste of expensive materials.
The success of the operation depends on preparation. If the surface is not degreased and there is moisture left in the compressor hose, even the most expensive spray gun will give away marriage. Therefore, pay close attention to the theoretical part, because every detail, from the choice of nozzle to the angle of inclination of the tool, affects the final appearance of the body of your car.
Selection and configuration of equipment: compressor and spray gun
The first thing the master faces is the selection of the compressor-spray gun combination. For painting a car body, the volume of air that the compressor can produce is critical. Low-power models designed for tire inflation are useless here, since they will not be able to provide stable pressure during the entire operating time of the torch. The optimal choice would be a unit with a receiver of 50 liters or more and an inlet capacity of at least 350-400 liters per minute.
The sprayer itself is better to choose a system HVLP (High Volume Low Pressure) or LVLP (Low Volume Low Pressure). The former require a large volume of air, but produce minimal fog and a high paint transfer coefficient (up to 65-70%). The latter are more air efficient and are great for garage conditions with not the most powerful compressors. 3–1.4 mm, and for acrylic primer or varnish - 1.5–1.7 mm.
Don't forget about the air preparation system. Moisture and oil are the main enemies of quality paint, causing craters and bubbles. Be sure to use oil/water separator, installed as close as possible to the spray gun handle, and also check it before each shift.
Setting up a tool before work is not a formality, but a necessity. Adjustment of the torch width, material supply and air pressure is carried out on a test surface (oak map) before starting work on the body. An incorrectly adjusted torch will lead to either excessive paint consumption or coating defects.
Safety precautions and workplace preparation
Working with paints and varnishes carries serious health risks, since solvent vapors and fine paint dust are toxic. Even if you work in a garage, having quality supply and exhaust ventilation is a prerequisite. The lack of proper airflow can lead not only to headaches, but also to the accumulation of explosive concentrations of solvent vapors.
The personal protection of the master must be comprehensive. An ordinary medical mask is not enough - you need a respirator with carbon filters of protection class A1 or A2. Safety goggles are also required to prevent vapor from entering the mucous membranes, and a special painting suit that does not lint.
⚠️ Attention: Never use open flame sources or sparking electrical appliances in the painting area. Solvent vapors are heavier than air and can accumulate in low areas, creating an invisible explosive cushion.
Preparing the room also includes wet cleaning the floor and spraying the walls with water to remove dust. Any speck of dust that gets on fresh varnish will ruin the appearance. The light should be bright and uniform, it is advisable to use fluorescent lamps located at an angle of 45-60 degrees to the surface in order to see defects and glare.
☑️ Checking readiness for painting
Adjusting the torch and air pressure
Before bringing the gun to the car, it is necessary to carry out a test spraying on a vertical oak card (a piece of cardboard or metal). This will allow you to visually assess the shape of the torch and adjust the settings. The ideal torch for applying base and varnish has an elongated oval shape with clear boundaries and uniform distribution of material over the entire area.
Adjustment is carried out by three screws on the body of the spray gun. A screw located on the trigger axis or on the side in the upper part is responsible for the width of the torch. The screw located at the bottom of the handle (or sometimes on the tank) regulates the flow of material. The third important parameter is the pressure at the inlet to the gun, which is set by the regulator on the pressure gauge (if it is built into the handle) or on the compressor gearbox.
Table of approximate settings for different materials
For soils, higher pressure and a wide nozzle (1.7-2.0 mm) are required, since the material is thick. For metallics, the pressure is reduced to avoid overdrying and shagreen. Varnishes are applied with medium pressure, controlling spreading. Always look at the technical data sheet (TDS) of the specific paint manufacturer for exact numbers, since the chemical composition is different for everyone!
If the torch has a “dumbbell” shape (double-horn), it means that the pressure is too high or the side horns of the nozzle are dirty. If the torch is round, you have not opened the side air channels. If there are smudges in the middle of the oval, you need to reduce the supply of material or add a little air.
| Material type | Nozzle diameter (mm) | Inlet pressure (bar) | Torch width |
|---|---|---|---|
| Soil filler | 1.6 – 2.0 | 2.5 – 3.5 | Maximum |
| Base enamel (metallic) | 1.3 – 1.4 | 1.8 – 2.2 | 20 – 25 cm |
| Acrylic varnish | 1.3 – 1.5 | 2.0 – 2.5 | 20 – 25 cm |
| Liquid putty | 2.0 – 2.5 | 3.0 – 4.0 | Maximum |
Application technique: movements and distance
The most important point in the work is the correct technique of hand movement. The spray gun should always be strictly perpendicular to the surface to be painted. If you tilt the gun (“play with your wrist”), the distance to the body in different parts of the torch will be different, which will lead to stripes and an uneven gloss effect.
The optimal distance from the nozzle to the surface is 15–20 cm. When approaching closer than 10 cm, there is a high risk of drips, and when moving further than 25 cm, the paint will dry in the air without having time to spread, forming dry shagreen ("orange peel"). The movement should begin before the trigger is pulled and end after the gun has passed the edge of the part.
⚠️ Attention: Do not stop moving your hand in the middle of the part. Any delay will lead to local accumulation of material and the formation of a difficult-to-remove sag.
The speed of movement must be uniform. Usually it is about 40–50 cm per second, but this depends on the viscosity of the material. The overlap of strips (passes) should be 50%. That is, when applying the second stripe, you must cover half of the first stripe already applied. This ensures uniformity of the layer and the absence of “bald patches”.
Keep your wrist locked. The movement should be carried out with the entire arm from the shoulder, and not just the hand. This ensures that a constant 90 degree angle to the surface is maintained throughout the entire pass.
When painting large surfaces such as the hood or roof, apply the material in stripes horizontally or vertically, but do not change direction within one coat. First, paint the ends of the parts (if required by the technology), then move on to the main planes.
Application of various types of materials
Each stage of painting requires its own approach. Priming is about creating a base, so a thicker layer is allowed here, but it is important not to overdo it so that the primer does not “boil”. Usually 2-3 wet layers are applied with drying between layers. The soil should lie flat, covering any risks from sanding.
The base enamel (color) is applied in thin layers. The first layer is often made “dusty” - semi-dry, in order to create adhesion for subsequent layers. The second and third layers are applied already wet, but without fanaticism. Metallics require special care: if the base is placed too wet, the metal may “float” or form a different tone. It is important to give each base layer time to matte (solvent evaporation) before applying the next one.
The final stage is applying varnish. Here they are no longer afraid to “pour”, the varnish should spread into the mirror. Usually 2 layers are applied: the first is thin (binder), the second is thick and wet. It is the second layer of varnish that forms the final gloss and depth of color.
The main rule of multi-layer coating: each subsequent layer is applied only after the previous one has lost its shine (matte) and the solvent has evaporated, but the dust has not yet settled.
Elimination of defects and instrument care
Even experienced craftsmen sometimes have defects. Drips (slips) are removed after complete polymerization of the varnish by carefully sanding and polishing. Shagreen (orange peel) can occur due to too viscous paint, high pressure or incorrect distance. Small shagreen can be removed by polishing; large ones will have to be repainted.
However, the best fight against defects is a clean tool. Immediately after finishing work, the spray gun must be disassembled and washed with solvent. Dried paint in the channels or on the needle will disrupt the geometry of the torch the next time it is used. Use pipe cleaners to clean the nozzle, but never use metal objects to clean the nozzle itself - this will scratch the calibrated hole.
After washing, lubricate the moving parts of the needle with a special lubricant to prevent it from souring. It is better to store the tool disassembled or in a special case protected from dust.
What to do if the paint starts bubbling (boiling)?
Paint boiling is usually caused by thinner evaporating too quickly (wrong thinner for the current temperature), being applied too thickly, or applied to poorly dried soil. The defect requires complete sanding to a smooth state and repainting.
What pressure should I set on the compressor?
The pressure at the outlet of the compressor (in the receiver) must be higher than at the gun, taking into account losses in the hose. Typically, 3.5–4 bar is set on the compressor gearbox so that at the inlet to the gun (with the trigger pulled) there is the required 2.0–2.5 bar.
Is it possible to paint in high humidity?
Highly not recommended. Humidity above 75-80% causes moisture to condense in the paint layer, causing clouding of the varnish (whitish coating) and loss of adhesion. In such cases, special retarded solvents and air dryers are required.