Cosmetic corrosion appears on external surfaces in the form of spot rust in places where the body comes into contact with overhead parts - decorative trims, lights, as well as on the edges of door flanges, hood, trunk lid. This type of corrosion appears primarily where the paintwork is damaged. Worsening the appearance of the car, cosmetic corrosion, if no measures are taken, progresses and turns into penetrating corrosion.
Penetrating corrosion affects the most difficult to visually check places of accumulation of moisture and dirt. It is detected when the damage caused by it is difficult to repair. The inner surfaces of box sections, surfaces of front and rear wings, thresholds and floor crossbars, the floor itself from the passenger compartment side, and the inner cavities of the doors are most susceptible to its impact.
Structural (through) corrosion affects the attachment points to the body of the power unit, chassis, elements that form the supporting frame of the body. Particularly susceptible to structural corrosion are elements that experience abrasive-corrosive effects - the bottom, thresholds, wheel arches, front and rear fenders. The loss of mechanical strength of these elements leads to the failure of the entire car body.
Repair areas affected by corrosion immediately upon discovering traces of corrosion on the paintwork or in areas where the mastic has peeled off.
The most radical method of removing rust is mechanical, although it is more labor-intensive. A combination of chemical and mechanical treatment of the affected areas is the most appropriate and effective.
Restoration of areas affected by corrosion is carried out in the following order.
To facilitate rust removal, wet the damaged area with white spirit or Omega-1 car cleaner. Remove corrosion products with metal brushes, scrapers of various shapes, spatulas, grinding wheels and sandpaper on a fabric or paper base.
Clean damaged areas from rust, old primer and paint, bitumen or plastisol coating until they have a metallic shine.
Rinse the cleaned areas with water, dry and degrease.
Apply a phosphating agent such as "Phosphator" with a brush.
Dry the treated surface for 25–30 minutes at a temperature of 18–20°C.
Apply a quick-drying phosphating or passivating primer with a low drying temperature to the prepared surface, such as VL-2 or VL-08 (phosphating primer, drying temperature 15-20°C, drying time 24 hours) or GF-073 or NC-097 (passivating primer, drying temperature 15-20°C, drying time 4 hours).
After the first layer has dried, apply a second layer of primer. Let it dry slightly and paint with decorative enamel.
Effective combating of structural corrosion is the most labor-intensive and expensive. It consists of inspecting the car, necessary disassembly and replacement of individual damaged body elements or removing damaged areas and welding pads to these places. Installing pads does not solve the problem, but only somewhat slows down the development of through corrosion of the body. Replacing damaged elements from spare parts or new elements will extend the service life of the body for another 10-15 years.
Restoration of paintwork is inevitable during the operation of any car.
To remove minor scratches that do not affect the body metal, follow these steps:.
Remove any loose paint particles by treating the damaged area with a fine sanding paste.
Rinse the treated surface with clean water, degrease and dry.
Apply a thin layer of paint to the scratch using a small brush.
Continue applying thin coats of paint layer by layer until the surface inside the scratch reaches the level of the surrounding panel surface.
Allow the new paint to cure for two weeks.
Sand the painted surface flush with the rest of the panel using very fine sanding compound.
Treat the repaired surface with wax.
If the scratch depth has reached the metal surface and caused corrosion, do the following:
- remove rust with a scraper;
- treat the surface with an inhibitor compound to prevent further development of corrosion deep into the metal;
- dilute the putty slightly with solvent and apply it with a rubber applicator (spatula) to the scratch;
- let the putty dry slightly;
- put a cotton glove on your hand, wet your index finger with solvent and run it along the scratch - a slight indentation should form on its surface;
- after the putty has dried, paint the damaged area.
Body puttying
Puttying before painting allows you to restore the geometric surface of the body panel being repaired. There are many types of body putties, but the best one works best with a hardener, you just need to strictly follow the manufacturer's recommendations. Putty is applied with a flexible rubber or plastic applicator. Mix a small amount of putty on a clean wooden or cardboard surface, using the hardener sparingly.
Apply putty in the following order.
Prepare the metal surface as described above.
Prepare the putty according to the manufacturer's instructions.
Apply filler to the damaged area of the body panel using the applicator. To achieve the desired surface contour and filler level, each stroke of the applicator should go through the entire repaired surface. As soon as the contour of the filled surface approaches the contour of the undamaged surface, stop applying the filler immediately, as it will begin to stick to the applicator as it hardens, forming lumps and leaving burrs.
Apply layers of paste at intervals of about 20 minutes until the level of the putty surface becomes slightly convex above the surrounding metal of the panel.
Allow the treated surface to dry and harden completely.
Remove excess putty with waterproof sandpaper: first with coarse-grained type N-180, then, gradually decreasing the graininess, finish processing with sandpaper N-600. It is recommended to use imported materials due to the higher quality of the abrasive and lining.
For best results, it is recommended to pre-wrap (or stick it on) paper around a wooden block (you can use rubber or foam).
During the processing, regularly and generously wet the sandpaper with water. Continue the work until the surface being processed is absolutely smooth.
At the final stage, the treated surface should appear as a disk or oval of clean surface, ending with a gradually tapering edge of well-preserved paint.
Rinse the treated area with plenty of running water to remove any fine abrasive particles formed during the sanding process.
Dry, degrease and dry the surface again with a hair dryer.
Apply a thin layer of primer from an aerosol can, thus revealing all the defects made during sanding.
Eliminate any defects found by applying a layer of fresh putty.
Repeat the sanding and polishing step.
Repeat the steps of filling, sanding and priming until you are satisfied with the result.
Text of the original source on this website (renaultbook)
Finally, rinse the treated surface with running water and dry it – now the surface is ready for painting.
Body painting
Painting of the panel surface should be carried out in a dry, clean and pre-ventilated room. The air in the room should be dry, clean and still.
Carry out painting in the following order.
Select the area of the panel to be painted; cover the rest of the surface with thick paper secured with adhesive tape. Leave an undamaged area of 50 mm wide open around the perimeter. Use thin paper (newsprint) in several layers.
Before painting, test the spray gun or aerosol can on an auxiliary surface (cardboard) and practice the coating application technique.
Prime the surface. The required thickness is achieved by applying multiple thin layers of primer. Dry the surface to be treated before applying each layer of primer.
Sand the surface with N-600 water-resistant sandpaper, using plenty of running water. Achieve absolute smoothness of the surface.
Allow the soil to dry completely.
Apply a layer of paint, again achieving its thickness through several layers (3–5). Apply layers "wet on wet", allowing the previous layer to dry slightly.
Start painting from the center of the area being repaired, moving your hand with the sprayer (with a spray can) in a spiral, expanding the radius of action until the entire damaged surface is covered, as well as a ring of the surrounding surface approximately 50 mm wide.
After 10-15 minutes, no later than after applying the last layer of paint, remove the paper and adhesive tape covering the body panel.
The paint is finally drying (polymerizes) within two weeks.
Only then begin to level out the color transition by treating the restored surface with a very fine grinding paste.
Finally, apply a layer of wax coating AB-70 to the restored panel. If less than 4 years have passed since the body was painted, then you can use car polish.
If after using the specified technology it was not possible to achieve satisfactory results, you can use the grinding paste of the PMA-2 brand. If this does not help, then you will have to completely repaint the body. Repeated use of PMA-2 paste is not allowed.
Elimination of minor body defects
The deformations of the outer surfaces that have arisen due to minor damage are eliminated in two ways - by punching and straightening, after which the paint coating is restored. If the use of a punch is difficult due to the impossibility of access from the back side, the damage is eliminated by external pulling and the use of polymeric materials.
To repair minor damage, follow these steps:.
Remove the old paint from the damaged area and prepare the surface as described above for painting.
Cover the surface cleaned to the metal with a grid of scratches, which will ensure maximum adhesion of the putty and the surface being treated.
Depending on the maximum depth of damage, prepare:
- polyester putty grade PE-0089, if the damage depth does not exceed 2.5 mm. Before use, mix the mass with the hardener (100:2.0) and apply with a spatula to the surface cleaned to a metallic shine and degreased;
- epoxy adhesive based on resin type ED-20, if the depth of damage does not exceed 4 mm;
- eP-0020 epoxy putty, if the damage depth does not exceed 7 mm. Before use, mix the mass with the hardener (100:8.5) and apply with a spatula to the surface cleaned to a metallic shine and degreased.
- Apply several thin layers of putty until the surface takes on a shape close to the original, with a slight protrusion above it.
Allow the putty to harden until it can be pressed through with a fingernail.
Proceed to prepare the surface for paint restoration as described above.
The highest quality of repair work is achieved by using polyester putties.