The process of restoring the paint coating of the car is aerobatics in body repair, where theoretical knowledge meets practical skills. Skill. paint properly It distinguishes the professional from the amateur, because it depends on the technique of application whether the boundary of the transition is visible or the surface will resemble an orange peel. Many novice craftsmen underestimate the importance of tool preparation and torch tuning, relying only on the quality of the enamel itself, which often leads to disappointment.
Modern dyeing systems, whether HVLP or LVLPThey require precise pressure calibration and an understanding of the physics of spraying. An error in choosing a dusa or an incorrect distance to a part can spoil even the most expensive paint. In this article, we will analyze all the nuances, from preparatory work to the final polishing, so that you can achieve a result indistinguishable from the factory.
It is worth noting that painting is not just a mechanical spraying of liquid, but a complex process that depends on many variables. The temperature in the chamber, the humidity of the air, the viscosity of the material and even the speed of the operator's hand play a critical role. Understanding these factors will allow you to avoid common defects and save significant money on reworking.
Selection of equipment and preparation of the spray gun
The first step to quality painting is to choose the right tool. To work with automotive enamels and varnishes, the most common systems are HVLP High Volume Low Pressure (HVL) which provides high transport of material to the surface at low pressure. This reduces fog formation and saves paint. Systems can be an alternative. LVLP, which are less demanding on the performance of the compressor, but also give an excellent result when properly adjusted.
The key element of the spray gun is the dusa (nozzle), the size of which is selected depending on the viscosity of the material used. For base layers (metallic, mother of pearl) usually use duzes with a diameter of 1.3-1.4 mm, while for acrylic enamels and varnishes, the optimal size will be 1.4-1.6 mm. The use of too wide dusa for liquid materials will lead to overflow, and narrow - to poor spraying of thick compositions.
⚠️ Attention: Never try to clean a clogged duz with metal objects or needles. This is guaranteed to damage the calibrated hole and the torch will become uneven. Use only special cleanses and solvents.
It is also important to pay attention to the materials of the body and needle. Stainless steel is preferable to brass, as it is resistant to aggressive solvents that are part of many automotive lacquers and flushes. High-quality spray gun has a system for adjusting the supply of air, torch and material, which allows you to flexibly adjust the tool for a specific task.
Preparation of paintwork
The quality of the final coating depends on the correctness of the preparation of the mixture by 70%. The paint must be thoroughly mixed to a uniform state, especially if it is a metallic or pearl, where heavy pigment particles settle to the bottom. After stirring, the composition must be filtered through a funnel with a mesh (usually 125 microns) to prevent the entry of foreign inclusions that can clog the duse or create defects on the surface.
The next critical step is to bring the viscosity to the working value. Viscosity is measured by a viscometer (funnel) and depends on the ambient temperature. For most materials, the optimal viscosity is 18–22 seconds at a temperature of 20°C. If the paint is too thick, it will not have time to spread, forming a shaking; if too liquid, there will be stains.
Dilution should be carried out strictly according to the manufacturer's recommendations, using recommended solvents. It is important to take into account the temperature in the paint chamber: in summer, “slow” solvents are used to make the paint spread, and in winter – “fast” to accelerate evaporation and avoid boiling.
Table of temperature and solvent correspondence
In summer (above 25°C) use solvents labeled Slow or Long. Autumn/Spring (15-20°C) – Normal or Standard. In winter (below 15°C) - Fast or Short. The use of an inappropriate solvent is the main reason for the matteness of the varnish.
Remember that the life of the prepared mixture is limited. After adding a hardener to two-component materials (acrylic, varnish), an irreversible chemical reaction begins. Cook as much paint as you can spend in 2-3 hours to avoid thickening the material directly in the tank.
Pressure setting and test spray
Before you bring the spray gun to the car, you need to conduct a test spray on paper or cardboard. This allows you to visually assess the shape of the torch and adjust the pressure. Pressure is measured at the exit of the gun at the time of the trigger. For systems HVLP The operating pressure is usually 2.0-2.5 atmospheres, for LVLP about 1.5-2.0 atmosphere.
The shape of the torch should be uniform, without breaks and seals at the edges. Adjusting the screw of the air supply, achieve an oval shape of the spot with clear boundaries. If there is a concentration of paint in the middle of the torch (“banana” or “dumbbell”), then the pressure is too low or the material is too thick. If the torch is too wide and dry, the pressure is excessive.
☑️ Checking the settings of the spray gun
Also at this stage, the overlap of the layers is checked. When conducting test strips on paper, each subsequent strip should overlap the previous one by about 50%. This ensures uniform application without strips and passes. Adjust the feed so that when you fully open the needle you get a rich, but not current coating.
Technique of applying paint to the body
The process of painting requires strict geometry of movements. The spray should always be located perpendicular to the painted surface. The inclination of the tool leads to an uneven distribution of the material: one part of the layer will be thicker, and the other - thinner, which eventually manifests itself in the form of a different tone or stripes.
The distance from the dusa to the surface should be 15-20 centimeters. If you hold the gun closer, there will be stains; if further - the paint will dry out in flight, lying dry dust, which will make the surface rough. The movement of the hand should be smooth, with a constant speed, starting the movement even before the trigger is pressed and ending after passing the edge of the part.
Start the movement of the hand 10-15 cm before the beginning of the part, press the trigger in the air and let it go also abroad. This will eliminate thickening at the beginning and end of the pass.
Painting is done by the method of “wet wet” or with interlayer drying, depending on the type of material. The base layer (metallic) is applied thinly, "in the fog" to avoid raising the solvent and the formation of bubbles. The varnishes, on the contrary, are applied with more greasy layers to create depth and gloss. It is important to observe the time intervals specified in the technical product map.
When painting large surfaces, such as a roof or hood, move around the part while maintaining the same distance and angle. Do not stop in the middle of the plane – this is guaranteed to lead to a local overflow. Rhythm and consistency are the key words for successful painting.
Coverage scheme and number of layers
To obtain a covert and smooth coating, it is necessary to follow the overlap scheme. Each passage of the torch must cover the previous one by 50%. This is a standard practice that provides double layer thickness throughout the area and hides possible flaws in the technique of hand movement.
The number of layers depends on the cover of the paint and the color of the substrate. Usually apply 2-3 layers of base and 2-3 layers of varnish. The first layer of the base is often called a “dust” or binder – it is applied very thinly to create adhesion for subsequent layers. The second and third layers are applied more saturatedly, but without the formation of subtexts.
| Type of material | Number of layers | Interlayer drying | Thickness of layer |
|---|---|---|---|
| Sound filler | 2-3 | 10-15 minutes | Tight, until the rice is filled |
| Base (metallic/pearl) | 2-3 | 5-10 minutes | Thin, translucent |
| Acrylic enamel (solid) | 2-3 | 10-15 minutes | Medium, covert |
| Lacquer (2K) | 2-3 | 10-20 minutes | Fat, glossy. |
Interlayer drying is the time it takes for the solvent to evaporate from the applied layer. If you do not stand a pause, the solvent will be “locked” inside, which will lead to boiling of the varnish, matteness or detachment of the coating in the future. Always focus on the technical maps of manufacturers, not on your feelings.
Proper overlapping of 50% and compliance with interlayer drying is more important than the amount of paint applied. It is better to make more thin layers than one thick one.
Typical defects and ways to eliminate them
Even experienced craftsmen sometimes have defects, but knowing the causes of their occurrence allows you to quickly eliminate the problem. One of the most common phenomena is “shagrene” (orange peel). It occurs due to too thick paint, high pressure or the wrong distance to the surface. Light shaven can be removed by polishing, heavy - only by repainting.
Subductions (inflows) are the result of excessive supply of material, too slow movement of the hand or close location of the spray gun. Fresh stain can be carefully removed by collecting excess soft cloth or tape, but if the varnish is already up, grinding and local polishing will be required.
⚠️ Attention: If you notice a stain on the varnish just applied, do not try to wipe it immediately. Give the material a little “grab” (10-15 minutes), otherwise you will smear the varnish and create a matte spot, which will have to repaint the whole.
Boiling paint (bubbles) is often caused by applying too thick layers without proper drying or using a quick solvent in hot weather. In this case, the solvent does not have time to exit and breaks the surface when heated. Treatment is one - complete grinding to the ground and repainting with compliance with drying regimes.
The matteness of the varnish can be a consequence of high humidity in the room, draft or moisture entering the air main of the compressor. Use water separators and monitor the temperature in the paint area. Sometimes matteness manifests itself after a while due to the incorrect proportion of mixing the components of the varnish.
Caring for tools after work
The quality of the next painting depends on how you wash the spray gun after the current one. Residues of paint dried in the channels or on the needle, can fall off at the next work and spoil the part. Immediately after the work is completed, wash the tank and the body with a solvent suitable for the used material.
Disassemble the gun: remove the air head, remove the needle and spring. Wash all the details in a solvent bath using soft brushes. Pay special attention to the air head - all its holes should be free from contamination. Blow the instrument with compressed air.
After washing, be sure to lubricate the moving parts (needle, trigger, adjustment screws) with a special lubricant for spray guns. Ordinary oil can dissolve in paints and spoil the next painting, so use only specialized means. Collect the tool and store it in disassembled form or with a weakened spring so that it does not lose elasticity.
How often should the rings be changed?
O-rings (gassing) should be changed at each sign of wear or if the spray gun began to “etam” the material in the off state. On average, with active professional operation, a complete replacement of the remix is recommended every 6-12 months. The use of aggressive solvents (e.g., to wash off old paint) may require more frequent replacement, as they break down Teflon and rubber.
Can I paint at high humidity?
Painting at humidity above 75-80% is not recommended. Moisture condensing on a cold metal or in a layer of paint leads to clouding of the varnish (white coating) and loss of adhesion. If the humidity is high, be sure to use air dehumidifiers in the chamber and heat the air at the inlet to the spray gun to reduce the relative humidity of the jet.
What to do if the paint starts to thicken in the tank?
If you work with two-component materials (acrylic, varnish) and the mixture began to thicken in the tank, it should be thrown away immediately. Add a solvent to the polymerization mixture can not be - it will violate the chemical structure and properties of the coating. Work in small portions to avoid losing material.
Do I need to heat the paint before painting?
The temperature of the material must be equal to the temperature of the surface to be painted and the environment (usually 20°C). If the paint is cold, it will be more viscous and can give condensation. If it is too warm, the solvent will evaporate faster. It is ideal to keep cans of paint in the room where the painting will be done, at least 24 hours before the start of work.