A small patch of rust on the car's body expands rapidly because the bare metal is exposed to moisture and air which causes it to oxidize or corrode. Whether you want to keep the car or sell it, you surely want the appearance to be in the best condition, so don't waste any more time and tackle the problem right away. Remove rust stains and repaint the body immediately to stop corrosion before it spreads.
Steps
Part 1 of 2: Polish and Repaint the Rust Stains
Step 1. Take basic security measures
This method involves the use of a grinder and a milling machine; they are both powerful electric tools capable of spreading micro-particles of rust and paint into the air. To avoid injury and protect your health from these powders, wear gloves and especially a mask, so you don't inhale them.
For very demanding jobs, consider getting a respirator instead of a simple mask
Step 2. Protect the areas you don't want to soil
As mentioned earlier, this process causes a lot of dust and if you don't pay attention it settles on the machine giving it a "scruffy" look that will be difficult to get rid of. To overcome this problem, protect all parts of the car on which you do not have to work (use adhesive paper tape). Under the machine fix a plastic sheet with adhesive tape to define the work area and protect the floor.
Covering the car is an art. Do not use newspaper sheets because the spray paint is able to impregnate them, staining the underlying surfaces. Instead, get paper specially designed for this job, because it is less porous and does not absorb color. Also be sure to seal every single edge of the card with masking tape. Don't use just small segments to hold the sheets in place, the paint will creep under any cracks left open
Step 3. Try to follow the shape of the body panels when lining them with the protective paper
In general, the sheet of paper must not stop in the middle of the panel, otherwise, during the painting phase, you will notice clear lines between the old color and the new one. These lines will not disappear with polishing or with many layers of clear finish, so avoid the problem and properly outline the work areas.
If you have a lot of experience with body painting, you can also consider not covering some panels adjacent to the rusted one. If you know how to gradually blend color with an airbrush, you can use this technique to make the transition from one shade to another less noticeable
Step 4. Remove the paint around the rust spot with a double action grinder
This type of tool allows you to control the rotation speed as you work. Start with an 80 grit abrasive pad and build up to 150 grit. This combination of abrasive power allows you to remove both the primer and paint layer, as well as light rust that has not fused to the metal. In addition, it smoothes and evens the surface.
Once finished, make sure with your hand (protected by the gloves) that the surface is smooth and homogeneous
Step 5. Switch to a circular cutter
Thanks to this you can eliminate any rust encrustation and expose the holes. When using the circular cutter be very careful and work slowly, as you could cause serious damage to the bodywork. Once this is done, apply an acid to remove the rust and to remove even the microscopic residues.
- For this work the most suitable product is phosphoric acid, you can buy it in auto parts stores.
- If you wish, fill the holes you left with specific putty, smoothing it out. Finish the application by sanding the filler by hand with 120 grit sandpaper, so as to make it very smooth. Read the next section for more details.
Step 6. Prepare the area before applying the primer
Buy one that is suitable for bare metal, as well as a spray paint that matches the color of the rest of the body. You can find both products in auto parts stores. There is a wide variety of primers, so follow the instructions on the label or ask your shop assistant for advice. Usually the preparation phase includes:
- Clean the area with white spirit or other thinner.
- Protection of the surrounding areas, for a radius of 90 cm, with adhesive tape and paper.
Step 7. Apply a thin, even coat of primer
Spray three coats, waiting a few minutes between applications. Don't overdo it, you don't have to spray so much primer that it drips or trickles down the body.
Most products require a drying time of at least 12 hours between coats
Step 8. Sand with water-based, 400-grit sandpaper
This material is specific for smoothing paint layers and matting surfaces, so that subsequent coats of color adhere better. Keep a bucket full of water handy to rinse the sandpaper frequently so it doesn't get stained with paint. Finally, wash the area with soapy water.
Step 9. Spray a thin layer of paint
Apply only thin coats and allow each layer time to "dry" before applying the second. In this way the paint does not become liquid and does not drip. Apply as many layers as needed to achieve the color tone you want.
Let the paint stabilize for at least 24 hours before removing the tape and backing paper. Be cautious, if you feel the color is still sticky, wait a little longer
Step 10. Polish the edges of the newly painted area so that it blends with the rest of the color
If necessary, also apply a layer of transparent finishing, so as to even more uniform the final appearance. Finally let the paint set for 48 hours.
Step 11. Wash and polish the car
Congratulations! You now have a rust-free and ready-to-drive car.
As a preventative measure, do not apply the wax for the first 30 days after painting. The friction generated during this procedure could peel off the fresh paint
Part 2 of 2: Using the Putty
Step 1. Drill the rusted area down to "bare metal"
This method is slightly different than the previous one, but the basic principles are the same, and it is also particularly suitable for rust that has caused holes and holes. For starters, use a round bur to remove all oxidation. You have to work until you encounter a "clean", rust-free metal layer, even if it means puncturing the bodywork.
- Getting rid of all corrosion is crucial; if you miss even a small chip, it will continue to "eat" the metal under the paint and soon another stain of rust will emerge.
- Remember to practice all safety measures suggested at the beginning of this article when using the grinder.
Step 2. Cover the hole with anti-rust putty
At this point you have to spread the putty in the point where there was previously the oxidation. You can find many products on the market, they are quite cheap and available in all auto parts stores. If it's a sizable hole, you'll need to improvise an alternative solution though. In this case, you need to provide the paint with a flat, strong base to adhere to and that won't rust at the same time. Secure this object with putty and wait for it to dry.
Believe it or not, a sliced can of soda or beer turns out to be a great "patch" in these cases. The aluminum in these items is, by nature, resistant to corrosion and most cans have a rustproof coating. A good alternative is a thin panel of hard plastic
Step 3. Use sandpaper to level the surface
Now you have to sand the "patch" with sandpaper so that you do not feel the difference with the rest of the body. It is a long and boring job; as you sand them, you may find that you need to add more grout. In this case, remember to wait for the new layer to dry before continuing with the sanding. This is a multi-stage job and you will need to be patient.
- Start with coarse sandpaper to smooth out larger imperfections and then gradually move on to one with a medium and then fine grit. In this way the surface will be perfectly smooth.
- Sand slowly, by hand and steadily for excellent results. Electric sanders may peel off your patch.
Step 4. Protect the rest of the bodywork
Now you need to apply the fresh paint on the rust-free area. It is therefore necessary to prepare the machine by protecting the parts not involved, as in the previous method. Don't forget the windows and tires.
As mentioned above, try to respect the shape of the body panels to hide the small differences in shade with the old paint (unless you are able to do a gradient paint)
Step 5. First apply the primer and then the color
Apply a few thin layers of primer waiting for it to dry between coats so that they adhere perfectly. Finally, wait for all the layers to dry overnight (12 hours at least) before sanding them with 400 grit sandpaper. When ready, you can apply the color using the same technique: "spray thin layers of color and wait for them to dry. between one hand and the other ".
- Again, you should blend and polish the transition zone between the old color and the new one. Then apply a layer of clear topcoat so that the final appearance of the bodywork is uniform.
- Obviously, it is crucial to purchase a paint whose color matches that of the rest of the car. Most auto parts dealers will be more than happy to help you choose; however, remember that, on older cars, the color has faded over time.
Advice
- A valid alternative to this long procedure: a good rust converter applied directly to the surface to be treated. Unlike the process described above, in this case you will not have to remove the rust and the paint layer completely. A rust converter is made up of two main elements: a tannin and an organic polymer. The organic polymer provides a protective layer, while the tannin reacts in contact with the iron oxide, transforming it into iron tannate, stopping and stabilizing the corrosion process. You can buy a rust converter at any auto parts store for a few dollars.
- If rust has affected the fender, it may be more convenient to jack up the car, using a wedge to lock the wheels, so that the car cannot move, and remove the wheel in the area to be treated. Also remove the plastic cover of the wheel arch, in order to repair any dents; you will have more space to work comfortably.
- A rust converter liquid is excellent for treating small chips, even if the oxidation process has not yet started. Pour a small amount into a paper cup (the compound, in contact with rust, will change its chemical properties and will no longer be reusable. Any excess will be eliminated). Using a toothpick, spread the product until it reaches the surface where the paint is still in excellent condition. Wait the time necessary for the treated area to dry completely. When the product is completely dry, a dull black stain will remain, similar to tar, hardly visible on dark colors. If you wish, use paint in the same shade as your car to touch it up and make it less visible.
- If rust has affected a large area of your car's body, see a professional.
Warnings
- If you want to use phosphoric acid, read and follow the instructions carefully shown on the product packaging.
- Always wear gloves, goggles, and a face mask to prevent paint dust and rust from causing health problems.
- Propellants can be explosive, so as long as you use them to remove rust, avoid using flames or causing sparks, especially don't smoke.
