Restoring paintwork is not just a cosmetic procedure, but a complex technological process that requires strict adherence to regulations. Car painting under varnish involves applying several layers of enamel followed by coating with a protective polyurethane composition, which gives the body depth of color and glossy shine. It is the finishing layer that protects the metal from corrosion, and the pigment from fading under the influence of ultraviolet radiation.
The quality of the final work directly depends on the surface preparation and conditions in the spray booth. Even a microscopic speck of dust falling on a fresh coat can ruin the appearance of the entire part, requiring labor-intensive polishing or repainting. Therefore, professionals devote 70% of their time to preparatory work, grinding and degreasing, leaving only 30% for the actual application of materials.
In this article, we will analyze all the nuances of the technology, from the choice of materials to final drying, so that you understand what you are paying for in the service or how to avoid mistakes when doing your own repairs. Color depth and the absence of shagreen (orange peel) are the main criteria for assessing the quality of a painter’s work.
Choice of materials: base, varnish and solvents
The basis of high-quality repairs lies in the right chemistry. Modern painting systems are most often built on the basis of water-soluble or solvent paints such as Base Coat, which do not contain protective properties and require mandatory varnishing. Varnish (Clear Coat) acts as armor, taking on all mechanical and chemical influences.
When choosing a varnish, it is important to pay attention to its hardness and dry residue. For cars operated in harsh conditions, two-component varnishes with a high dry matter content (HS - High Solid) are recommended. They provide a thicker layer that is easier to polish and better hides minor defects in the substrate.
Solvents and thinners are selected strictly according to the temperature in the chamber. Using a fast solvent in hot weather will cause the paint to boil (“shagreen”), and using a slow solvent in cold weather will lead to drips and long drying times. Selection of solvent carried out according to the ambient temperature: fast for +20°C and above, medium for +15...+20°C, slow for operation below +15°C.
Always use solvents and varnishes from the same manufacturer as the base paint. Mixing brands may result in chemical incompatibility and swelling of the coating.
Below is a table of the main types of varnishes and their characteristics for various tasks:
| Varnish type | Dry residue | Application | Polishability |
|---|---|---|---|
| MS (Medium Solid) | Average (~40-45%) | Local repairs, small parts | Average |
| HS (High Solid) | High (~50-60%) | Full paint, body parts | Excellent |
| UHS (Ultra High Solid) | Very high (>60%) | Premium segment, maximum protection | Excellent |
| VHS (Very High Solid) | Maximum | Special equipment requiring a thick layer | High |
Surface preparation: the key to an ideal result
No paint, even the most expensive, can hide preparation defects. Puttying and sanding is the foundation on which the entire paint layer rests. If you skip the stage of leveling the microrelief, all defects will appear after applying the varnish, since it works like a magnifying glass.
The process begins with stripping the old coating down to metal or soil in areas of corrosion. Then an epoxy primer is applied to protect against moisture and an acid (phosphate) primer for adhesion. This is followed by a layer of filler (acrylic primer), which levels the surface and hides the marks from sandpaper.
☑️ Preparing the body for painting
It is important to observe the gradation of abrasives. If the primer was sanded with a P500 mark before painting with a metallic paint, then streaks may appear after the varnish shrinks. For solid colors, a finer sanding of P600-P800 is required. Degreasing should be carried out twice: before priming and immediately before painting, using lint-free wipes.
Base enamel application technology
Applying the Base Coat is the most crucial moment that determines color rendition. The paint is applied in 2-3 layers with interlayer drying (exposure) for 10-15 minutes at a temperature of +20°C. The first layer is done with “spray” to create an adhesive film, the subsequent ones are done wet, but without the formation of drips.
The peculiarity of metallics and pearls is that the direction of the phalet (metallized particles) depends on the spraying technique. If you hold the gun at a different angle or change the distance, the color may vary in different areas of the part. This phenomenon is called "variation of tone".
⚠️ Attention: It is strictly forbidden to touch the surface of the base with your hands, even with gloves. Fatty fingerprints will appear after varnishing in the form of matte spots that cannot be polished.
After applying the last layer of base, you need to let it dry completely (“matte”). The holding time is usually 20-30 minutes, but depends on humidity and temperature. If you rush and apply varnish to a sticky base, the solvent from the varnish can “boil” the paint, creating irreversible defects.
Why does the base become matte?
During the drying process, the solvent evaporates from the paint surface, making it rough at the micro level. This is normal and necessary for the varnish to adhere.
Applying varnish: creating depth and protection
The varnish is applied to the prepared base in two stages. The first layer is a binder, applied thinly so as not to dissolve the base excessively. The second layer is the main one, it goes on more thickly, creating that same mirror effect and depth. Wait 10-15 minutes between layers to allow the solvent to evaporate.
The technique of working with a spray gun when varnishing requires special smoothness. The torch should lie exactly 50% of the previous pass. Sudden movements or stopping the hand will lead to swelling. Inlet pressure into the gun is usually 2-2.5 atmospheres, but the exact values depend on the model of the spray gun and the viscosity of the material.
After applying the final layer, the car is left in the chamber for primary polymerization. It is important to prevent dust from entering during the first 30-40 minutes while the varnish is in the liquid phase. Any speck that falls at this point will require subsequent sanding and polishing.
Drying and polymerization of the coating
The drying process is divided into two types: natural and forced (heat chamber). Natural drying at +20°C takes about 24 hours to reach full strength, although “drying” occurs after an hour. Accelerated drying in a chamber at +60°C allows you to reduce the time to 40-60 minutes.
Heat treatment is necessary for proper polymerization of the varnish. As the temperature rises, the molecules of the binder join together more actively, creating a stronger and more elastic structure. Under-dried varnish will be soft, which will lead to rapid scratches and problems during polishing.
⚠️ Attention: Sudden cooling of a hot car (for example, opening a camera gate in winter) can cause clouding of the varnish due to moisture condensation inside the coating that has not yet cooled down.
Complete crystallization of the varnish occurs within 7-14 days (for some materials up to a month). During this period, it is not recommended to wash the car with aggressive chemicals, use abrasive polishes, or subject the body to high-pressure washes at an angle of 90 degrees.
Finishing and polishing
Even in an ideal chamber, “shagreen” (orange peel) can form on the varnish or dust can enter. To eliminate these defects, abrasive polishing is used. The process begins with grinding the surface with water or “dry” with P1500-P3000 grade abrasives.
After sanding, the surface becomes matte. The next stage is restoring the gloss using polishing pastes. First, a coarse abrasive is used to remove marks, then a fine one to add shine. Polishing returns the mirror finish to the coating and removes differences in shagreen between new and old paint.
The final stage is often applied with a ceramic coating or liquid glass. These compounds create an additional hydrophobic layer that facilitates car care and protects fresh varnish from reagents and bitumen in the first months of operation.
High-quality polishing can hide minor paint defects and even out shagreen, making the transition between old and new paint imperceptible.
Common mistakes and how to avoid them
One of the common mistakes is temperature violation. Painting in a cold room (< below +15°C) without heating means that the varnish does not spread, forming large shagreen, and the solvent does not have time to evaporate, causing clouding.
Incorrect spray pattern settings are also common. A torch that is too narrow will cause streaks when applying varnish, while a torch that is too wide will result in a lot of fog and waste of material. Dew point - another critical parameter: if the humidity in the chamber is above 70-75%, “silicone” (oily spots) or a whitish coating may appear on the varnish.
Ignoring the interlayer drying time is a direct path to defects. If you apply varnish to an under-dried base, the solvents will get trapped inside, which will lead to boiling and bubbles. If the base is left too long (more than 24 hours without varnishing), adhesion may deteriorate and additional matting of the surface will be required.
How long does it take for a car to dry after painting?
Initial drying “from dust” takes 30-60 minutes in the chamber. The car can be used after 24 hours. Complete polymerization and maximum hardness occur within 14-30 days, depending on the type of varnish.
Is it possible to paint a car in the garage in winter?
Technically possible, but extremely difficult to ensure cleanliness and temperature. Garage dust contains a lot of lint and dirt that will ruin the varnish. It is also difficult to warm up the entire volume of air and the body evenly, which will lead to drying defects.
Why did the varnish fade after drying?
The reasons may be high humidity, the use of low-quality solvent, too thick a layer of varnish or insufficient ventilation during drying. It is also possible for the surface to oxidize due to contact with air prior to polymerization.
Does new paint need to be buffed?
Under ideal camera conditions and if the painter is highly skilled, polishing may not be necessary. However, in practice, light polishing always improves the appearance, removes dust particles and evens out shagreen, making transitions less noticeable.
What is the difference between an expensive varnish and a cheap one?
Expensive varnishes (HS, UHS) have a larger dry residue, spread better, give a deeper gloss and are highly resistant to scratches and UV radiation. Cheap varnishes fade faster, turn yellow and require more frequent polishing.