It is necessary to distinguish between types of damage to body surfaces:
- deformation of the surface without damaging the paintwork;
- surface damage with metal deformation;
- damage to the paintwork with a violation of the primer and putty layer;
- coating damage (scratches) without disturbing the primer and putty layer.
Depending on the type of damage, one or another repair technology is chosen.
Since during repair work it is necessary to act 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 instrument. 50% of success depends on the quality of the tool. The remaining 50% must be attributed to the hands of the performer.
Correcting irregularities is called straightening. To perform straightening work, they use: wooden and nylon hammers of various shapes and sizes; supports also of various sizes and shapes, mostly metal, massive, playing the role of an anvil; supports are massive, but elastic (rubber). Experienced straighteners widely use straightening saws, but great skill is required to use them. An important role in the repair work is played by abrasive skins. Most often, a waterproof sanding paper is used, produced in sheets of 220X310 mm in size. 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 grit number of the sandpaper. For grinding the old paintwork, that is, if the coloring is to be done on the old paint, use the skins KZ-12, KZ-10, KZ-8. For grinding puttied and primed surfaces, KZ-6, KZ-5, KZ-4 skins are used.
Equally 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. Not without reason, viscosity is indicated in all recommendations for the preparation of materials. Fluidity, lack of streaks, coating thickness, etc. depend on the correctly chosen viscosity. To obtain the material of the desired 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, passing into a cone with a hole with a diameter of 4 mm. The glass is filled to the top with paint, having previously clamped the hole in the cone. Then the hole is opened and, turning on the stopwatch, measure the time for the paint to flow from the glass into the container. That is why viscosity is measured in seconds. To achieve the required viscosity, a solvent is added to the prepared composition (if you need to reduce the viscosity) putty, primer, enamel.
If there is no viscometer, then the paint is prepared by eye and with the help of a spray gun, a test coloring is carried out on a metal sample, while making sure that the paint has a normal spill and does not flow from a vertical surface.
When filling work, it is most convenient to use steel or rubber spatulas. For steel spatulas, steel grade U7A-02 is used. It is better when the thickness of the spatula is variable, and increases from the blade to the handle. Blades are usually 30-100 mm wide and 2 mm thick. These spatulas are almost eternal.
Rubber spatulas made from resilient sheet rubber are also widely used. The size of the spatulas is 64X45X5 mm, and the edge (blade) sharpen.
A wide variety of systems, from commercially available to homemade, are used as material sprayers during repair work. Given the small size of the areas to be reclaimed, the performance of the selected spraying media may be low.
At home, again given the small size of the areas to be restored, electric heaters can be effectively used to speed up the drying of puttied, primed and painted surfaces. The most common drying method during repair work is an electric lamp. Lamps of the ZC 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 equal to 200-300 mm. For 40-50 minutes, this method ensures reliable drying of the treated surfaces.
For drying small surfaces in 1 hour, an ordinary medical reflector located at a distance of 50-60 mm is also suitable.
When using such devices, the safety regulations must be strictly observed.
It happens that dents have formed on the surface of the body, and the paintwork is not broken. Most often this happens on the flat surfaces of the rear fenders and front doors. There is a so-called «clapperboard». 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 it is not possible to restore the surface by simply pressing, a tool is used. Support in this case should be massive, but not solid (e.g. a piece of thick rubber), and several layers of fabric should be applied to the head of the nylon hammer. Tightly pressing the rubber bar against the inner surface of the dent, gently hammer the surface from the edges to the middle with a hammer, gradually removing the dent.
Deep dents with broken paintwork begin to rule 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, it is impossible to apply force, since the metal is flattened and enlarged 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 KZ-6 sandpaper and degreased with white spirit. Without much experience in straightening, it is difficult to achieve a flat surface. There are bound to be minor imperfections (0.5-1.0 mm). It is best to eliminate them with a commercially available epoxy putty. Putty is applied with a metal or rubber spatula with a layer sufficient to fill all existing irregularities. After 24 hours of natural drying (after complete drying) it is necessary to clean the putty surface with abrasive sand 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 a preliminary, rough polishing. Finally, the surface is polished with KZ-4 sandpaper. There should be no visible scratches or scratches on the sanded surface. After grinding, the surface is washed with water, wiped and dried under natural conditions for at least 1 hour.
Considering that the putty filled only the cavities and when grinding, areas of bare metal will definitely appear (those that were knocked out during straightening are somewhat larger than necessary), part of the treated surface is covered with primer VL-08 or paint. This primer is able to create on the metal surface simultaneously with the protective film a layer of insoluble phosphate salts that protect the metal from corrosion. With a small area of treatment, the primer can be applied with a swab, providing a thickness of at least 6-10 microns.
If, after the performed operations, there are still some irregularities on the surface, use the quick-drying putty MS-00-6, which is applied with familiar spatulas. After 1-2 hours of natural drying (15-20 min with a reflector) the surface is polished with a waterproof sandpaper KZ-4, washed with water and dried dry. After processing with putty MS-00-6, it is necessary to apply on the entire surface to be treated (best with a spray bottle) a layer of epoxy primer EF-083, designed specifically for the repair of VAZ car bodies. Soil EZF-083 has good performance. It has the necessary hardness and high anti-corrosion properties. In order for the quality of the surface to be painted to be high, the soil 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 the car for partial painting (body parts), then the part on which the repair was carried out is painted in its entirety, 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 a part of a part, for example, doors, but this is done only when it is possible to beat off a clear border on the part, i.e. there is an edge up to which you can paint and hide the border of the old and new coatings. In practice, when repairing painting, it is impossible to accurately match the color that matches the old coating, and it is also difficult to hide the border between the old and new coatings. These difficulties must be taken into account and the surface to be painted must be prepared within such limits 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 repaired one must be sanded before painting, and then wiped with gasoline.
VAZ cars are painted with ML-197 synthetic enamels. The same enamels are used to repair the coloring. Enamel ML-197 (like other synthetic enamels) does not crack, wears little and has high mechanical strength. The total thickness of the paintwork 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). Starting painting, you should protect the car from pollination. 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 a straight line, use a medical plaster. Some coat adjacent surfaces with a specially formulated compound consisting of 30% glycerin, 20% dextrin, 40% chalk, and 10% water. The composition is easily washed off with water. It is only necessary to ensure that it does not get on the surface to be painted.
Very carefully should be taken to the preparation of enamel. This equally applies to the preparation of putty, primer. Preparation consists in thoroughly mixing the paint, diluting to the required viscosity and filtering. After opening the vessel with paint, it is necessary to remove the surface film, and then mix the paint well with a clean wooden stick. As a solvent for ML-197 enamels, R-198 is used, as well as xylene, toluene, solvent No. 651. 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 cheesecloth, folded in 2-3 layers.
For car painting, the following materials are used in an amount per 1 m2 (numbers are given in brackets) and for the car as a whole (kg):
- Ground - (0,120—0,150) 4,0
- Enamel - (0,900—0,110) 6,0
- Solvent - (0,100) 20% by weight of material
The surface is spray painted and the first coat is usually applied with a paint having a viscosity of at least 26 s. Between the first and second layers make an exposure of 5-7 minutes. The second and third layers are applied with a more liquid paint having a viscosity not higher than 26 s.
A lot of trouble when painting delivers dust. It is difficult to avoid it at home, so they are looking for ways to reduce its concentration. If you have to paint in the garage, the room is moistened by nailing dust. It is more expedient to paint the car in the yard, in a place protected from all sides from the wind, and in the early morning hours, when it is usually calm.
An important circumstance affecting the quality of painting is the purity of the incoming compressed air necessary for spraying the paint. If the air comes from a centralized line or from a compressor, then mineral oil or water can enter the paint. Both oil and water adversely affect the quality of the color. Oil leads to the formation of shells (craters), and the water creates bubbles under the paint layer.
To clean the air, it is necessary to install an oil-water separator in front of the atomizer.
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 established that the higher the temperature, the more intense the polymerization process, the quality of the film, especially water resistance and hardness, increase. The optimum drying temperature for ML-197 enamel is 100–130°C. In this case, 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's 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 method has its downsides. So, catalysts somewhat change the shade of dyes, which is especially noticeable in light colors. It is dangerous to work with concentrated hydrochloric acid, so natural drying remains the most developed 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 what the protection is when painting, the smallest particles will still find bare areas, stick and make the recently shiny surface matte. Moisten a soft cloth with gasoline or thinner, wipe the dusted surfaces with it, and then dry with a clean cloth.
If in some parts of the body there is damage to the paintwork that does not require a primer and putty, the coating is restored as follows. The surface is washed and sanded using waterproof sandpaper K3-4 and K3-3. The polished 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 with a gun. After 5-7 minutes, a 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 of xylene or solvent and one part of turpentine is applied from a spray gun to a damp painted surface. The role of this composition is to provide a uniform shine.