It is necessary to distinguish between the types of damage to the body surfaces:
- deformation of the surface without damaging the paintwork;
- surface damage with metal deformation;
- damage to the paintwork with disruption of the primer-putty layer;
- damage to the coating (scratches) without damaging the primer-putty layer.
Depending on the type of damage, one or another repair technology is selected.
Since repair work involves working on surfaces made of thin (0.6-0.7 mm) sheet metal and painted with a thin layer of enamel, special attention should be paid to the tool. 50% of success depends on the quality of the tool. The remaining 50% should be attributed to the hands of the performer.
Straightening out irregularities is called straightening. To perform straightening work, use: wooden and nylon hammers of different shapes and sizes; supports also of various sizes and shapes, mostly metal, massive, playing the role of an anvil; the supports are massive but elastic (rubber). Experienced bodybuilders widely use bodybuilder saws, but great skill is required to use them. Abrasive papers play an important role in repair work. Most often, waterproof sanding paper is used, produced in sheets measuring 220X310 mm. Each sheet is marked, for example, KZ 10-5, where KZ is green silicon carbide, the number 10 indicates the percentage of silicon oxide in the grain, and the number 5 is the grain size of the sanding paper. For sanding old paintwork, i.e. if painting is to be done over old paint, use sandpaper KZ-12, KZ-10, KZ-8. For sanding putty and primed surfaces, use sandpaper KZ-6, KZ-5, KZ-4.
No less important is the role of tools and devices in the preparation and application of liquid materials (putties, primers and enamels). First of all, a few words about the viscosity of materials. It is not without reason that viscosity is indicated in all recommendations for the preparation of materials. The spreadability, absence of drips, coating thickness, etc. depend on the correctly selected viscosity. To obtain a material of the required viscosity, a special device is needed - a viscometer. The device is simple in design, and you can make it yourself.
The viscometer consists of a glass (plastic, metal) with a capacity of 100 cm³, turning into a cone with a hole of 4 mm in diameter. The glass is filled to the top with paint, having previously clamped the hole in the cone. Then the hole is opened and, having turned on the stopwatch, the time of flow of paint from the glass into the container is measured. This is why viscosity is determined in seconds. To achieve the required viscosity, a solvent is added to the prepared composition (if you need to reduce viscosity) putty, primer, enamel.
If there is no viscometer, then the paint is prepared by eye and a test painting is carried out on a metal sample using a spray gun, making sure that the paint has a normal flow and does not run off the vertical surface.
When filling, it is most convenient to use steel or rubber spatulas. For steel spatulas, use grade U7A-02 steel. It is better when the spatula thickness is variable and increases from the blade to the handle. Blades are usually 30-100 mm wide and 2 mm thick. Such spatulas are practically eternal.
Rubber spatulas made of elastic sheet rubber are also widely used. The size of the spatulas is 64X45X5 mm, and the edge (blade) is sharpened.
A wide variety of systems are used as material sprayers during repair work, from commercially available ones to homemade ones. Given the small size of the areas being restored, the productivity of the selected spraying means may be low.
At home, again, given the small size of the restored areas, you can effectively use electric heaters to speed up the drying of putty, primed and painted surfaces. The most common method of drying during repair work is an electric lamp. Lamps of the ZS type for 127 or 220 V with a power of 250-500 W are installed on racks. The distance from the lamps to the painted surface is set to 200-300 mm. In 40-50 minutes, this method ensures reliable drying of the treated surfaces.
For drying small surfaces in 1 hour, a regular medical reflector located at a distance of 50-60 mm is also suitable.
When using such devices, you must strictly follow safety regulations.
It happens that dents on the surface of the body are formed, and the paintwork is not damaged. Most often this happens on the flat surfaces of the rear wings and front doors. The so-called "clap" occurs. To remove such a dent, no tool is needed. You need to get to the inside of the deformed surface and press it with your hand. If simple pressing does not restore the surface, use a tool. The support in this case should be massive, but not hard (for example, a block of thick rubber), and several layers of fabric should be placed on the head of the nylon hammer. Pressing the rubber block tightly against the inner surface of the dent, the hammer carefully beats the surface from the edges to the middle, gradually removing the dent.
Deep dents with damaged paintwork are straightened from the middle to the edges. In this case, a massive metal support with a flat and smooth working surface is used as a support. When straightening a deformed surface, you cannot apply force, since the metal is flattened and increases in size due to thinning from impacts, and it is no longer possible to achieve the original geometry of the part. The leveled surface is cleaned with sandpaper No.16-20, then finally - with sandpaper KZ-6 and degreased with white spirit. Without much experience in straightening, it is difficult to achieve a flat surface. Small irregularities (0.5-1.0 mm) will definitely remain. It is best to eliminate them with epoxy putty, which is available on the market. The putty is applied with a metal or rubber spatula in a layer sufficient to fill all the existing irregularities. After 24 hours of natural drying (after complete drying) it is necessary to clean the putty surface with abrasive sandpaper No.12, which for ease of use is placed on a wooden or foam block and sanded in one direction, washing off the abrasion products with a stream of water. This is preliminary, rough sanding. The surface is finally sanded with sandpaper KZ-4. There should be no visible marks or scratches on the sanded surface. After sanding, the surface is washed with water, wiped and dried in natural conditions for at least 1 hour.
Considering that the putty only filled the depressions, and that when sanding, areas of exposed metal will inevitably appear (those that were knocked out during straightening were slightly larger than necessary), part of the surface to be treated is covered with VL-08 primer or paint. This primer is capable of creating a layer of insoluble phosphate salts on the metal surface simultaneously with the protective film, protecting the metal from corrosion. For a small area of treatment, the primer can be applied with a swab, ensuring a thickness of at least 6-10 microns.
If after the operations performed there are still some unevenness on the surface, use quick-drying putty MS-00-6, which is applied with the already familiar spatulas. After 1-2 hours of natural drying (15-20 minutes with a reflector), the surface is sanded with waterproof sandpaper KZ-4, washed with water and dried dry. After processing with putty MS-00-6, it is necessary to apply to the entire surface being treated (best with a spray bottle) a layer of epoxy primer EF-083, designed specifically for repairing VAZ car bodies. The EZF-083 primer has good performance. It has the necessary hardness and high anti-corrosion properties. In order for the quality of the painted surface to be high, the primer layer must be well dried. The surface prepared in this way is almost ready. It remains to wipe the places to be painted with gasoline.
At service stations, if they take a car for partial painting (body parts), then the part on which the repair was carried out is painted entirely, regardless of the fact that the prepared surface is only 10% of the area of the entire part. Sometimes it is decided to paint only part of the part, for example, the doors, but this is done only in the case when it is possible to beat off a clear border on the part, i.e. there is an edge up to which it is possible to paint and hide the border of the old and new coatings. In practice, when painting repairs, it is impossible to precisely select a color that matches the old coating, and it is also difficult to hide the border of the old and new coatings. These difficulties must be taken into account and the surface to be painted must be prepared within such boundaries that the work performed does not look like a patch. It should be remembered that the part of the surface that has to be painted together with the one being repaired must be sanded before painting and then wiped with gasoline.
VAZ cars are painted with synthetic enamels ML-197. The same enamels are used to repair paintwork. Enamel ML-197 (like other synthetic enamels) does not crack, wears little and has high mechanical strength. The total thickness of the paint coating should be 70-120 microns. To achieve this thickness, while maintaining good adhesion to the preparatory layers, it is necessary to paint in three layers (at least). When starting to paint, you should protect the car from dusting. There are several ways to protect. Surfaces adjacent to the area to be painted are covered with paper. If it is necessary to beat off an even line, use a medical plaster. Some cover adjacent surfaces with a specially prepared composition consisting of 30% glycerin, 20 dextrin, 40 chalk and 10% water. The composition is easily washed off with water. You just need to make sure that it does not get on the surface to be painted.
It is necessary to be very careful when preparing the enamel. This applies equally to the preparation of putty, primer. Preparation consists of thoroughly mixing the paint, diluting to the required viscosity and filtering. After opening the container with paint, it is necessary to remove the surface film, and then mix the paint well with a clean wooden stick. R-198, as well as xylene, toluene, solvent No.651 are used as a solvent for ML-197 enamels. The working viscosity of the enamel should be within 25-30 s at a temperature of 18-23°C. Then the paint is filtered through gauze folded in 2-3 layers.
For painting a car, the following materials are used in quantities per 1 m² (the numbers are given in brackets) and for the vehicle as a whole (kg):
[The original source is published on the website: vazbook.ru]
- Soil - (0.120—0.150) 4.0
- Enamel - (0.900—0.110) 6.0
- Solvent - (0.100) 20% of the material weight
The surface is painted by spraying, and the first layer is usually applied with paint having a viscosity of at least 26 s. Between the first and second layers, a 5-7 minute hold is made. The second and third layers are applied with a more liquid paint having a viscosity of no more than 26 s.
Dust causes a lot of trouble when painting. It is difficult to avoid it at home, so ways to reduce its concentration are sought. If you have to paint in the garage, the room is moistened, knocking down the dust. It is more advisable to paint the car in the yard, in a place protected from the wind on all sides, and in the early morning hours, when there is usually no wind.
An important factor that affects the quality of painting is the purity of the incoming compressed air required for spraying the paint. If the air comes from a centralized line or from a compressor, it is possible that mineral oil or water will get into the paint. Both oil and water have a detrimental effect on the quality of painting. Oil causes cavities (craters), and water creates bubbles under the paint layer.
To clean the air, it is necessary to install an oil-water separator in front of the sprayer.
The most difficult issue when painting at home is drying the painted surface. When drying synthetic enamels, two phases of the process occur: first, the evaporation of solvents, and then the formation of a film, its formation under the influence of high temperature. Research has shown that the higher the temperature, the more intense the polymerization process, the higher the quality of the film, especially water resistance and hardness. The optimal drying temperature for ML-197 enamel is 100-130°C. At the same time, for light-colored enamels, the lower limit will be most suitable, since yellowing of the coating is possible.
To reduce the drying temperature, catalysts are used: Petrov contact, dibutylphosphoric acid (2-4%). There are cases when concentrated hydrochloric acid is added to the enamel prepared for painting (10-30 g per 1 kg of paint). This significantly reduces the drying time in natural conditions. However, each of the methods has its negative sides. Thus, catalysts somewhat change the shade of the dyes, which is especially noticeable on light tones. It is dangerous to work with concentrated hydrochloric acid, so natural drying remains the most proven option. It will take a lot of time (at least 3 days.), but this coating will be clean and reliable.
Experience has shown that no matter how much protection is provided during painting, the smallest particles will still find exposed areas, stick and make the recently shiny surface matte. Wet a soft cloth swab with gasoline or solvent, wipe the dusted surfaces with it, and then dry with a clean napkin.
If damage to the paintwork occurs on individual sections of the body that does not require priming and puttying, the coating is restored as follows. The surface is washed and sanded using waterproof sandpaper K3-4 and K3-3. The sanded surface is washed with water and wiped dry. After 1-2 hours, the first layer of enamel with a viscosity of 26-28 s is applied using a gun. After 5-7 minutes, the second layer is applied, but the paint is made more liquid, with a viscosity of 24-26 s. Sometimes a composition consisting of seven parts xylene or solvent and one part turpentine is sprayed onto the wet painted surface. The role of this composition is to ensure a uniform shine.