Mending Scratches to Cars

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All scratches are not necessarily  the same. Some  may not even be scratches at all. You find these when a painted car bumper or wooden post, or the rubber bumper on a shopping cart, rubs up against the body of the car. The object doing the rubbing may be softer than the paint. Instead of scratching the car, it deposits material on the surface — a mark that is actually raised above the paint, not gouged into it.

If the object is harder than the paint, guess where the material gets transferred? From your car to the shopping cart, leaving paint missing. Some scratches can be rescued, while others can’t.

But many marks simply “scratch the surface,” as it were. The offending object gouges the clearcoat and even some of the base color, while leaving the primer and metal unscathed. When there’s still color at the bottom of the scratch it may be possible to remove it with some careful sanding, buffing and waxing.

You don’t need fancy tools to distinguish a scratch from a mark. A fingernail drawn over the surface at 90 degrees to the defect will tell you if it’s gouged into the paint or sitting on top of it. If it’s a mark that appears to be from rubber, plastic or even other paint, it may come off easily with an aerosol tar or adhesive remover. Stubborn marks often can be removed with acetone or lacquer thinner on a soft rag. If the mark is still there after using one of these solvents, try hand rubbing or polishing compound. First, clean the area with soap and water, then spread rubbing compound on the mark and rub the area in a circular motion until the mark disappears. Once it’s gone, switch to a back-and-forth motion to remove circular buffing marks. Buff the area with a clean cloth to remove rubbing compound. Then, using a fresh pad, clean the area with polishing compound to remove the fine scratches left by the rubbing compound. Finish by sealing the surface with a good car wax.

If the defect is a scratch, determine if it extends below the surface of the paint and into the primer. Sometimes one end of the scratch looks fine but the other end gets deeper and deeper until it breaks through into the primer and the metal underneath. How much of that scratch is below the colour? If it’s a small portion of the scratch, you may want to repair what you can, and just try to ignore the rest until you’re prepared to repaint the panel.

Modern cars now are almost always clearcoated over the colour layer of the paint. This is done to provide a shinier finish, as well as to prevent ultraviolet light from fading the pigment underneath it.

Scratches in clearcoat can similarly be sanded out. However, if you sand completely through the clear into the color underneath, you have to respray the clear on that panel. That’s still easier than trying to match the color of the original paint, spraying the panel and then clear­coating over it. If the scratch goes into the primer, you’ll be forced do exactly that.

To repair a scratch, start by washing the panel with soapy water and then drying it thoroughly. To fix the scratch you won’t really be removing it at all. Rather, you’ll be sanding down the paint surrounding the damaged area until they are both at the same level. As you might guess, the goal is to sand down to the level of the scratch without sanding through to the next layer.

To make sure you don’t go too far, rub a material into the scratch that contrasts with the paint color. In the case of our red Porsche photo car, we used black shoe polish. If the car is a dark color, white shoe polish, Wite-Out or another light-colored material will work. Once the contrasting color is in the scratch, sand remaining material from the paint surface.

The key to sanding safely is to use an ultrafine 2000- to 3000-grit wet/dry sandpaper, which is available at auto parts stores where body shop supplies are sold. Place the paper on a rubber sanding block or a wood block, then dip it in a bowl of cold water. Add two or three drops of liquid dish detergent to make the water more slippery and to improve cutting action. Sand the scratch area using light, short strokes at alternating 60-degree angles to the scratch. Move up and down the length of the scratch, stopping frequently to rinse the paper in the water. The goal is to work slowly and lightly until you see the contrasting mark disappear.

Once it is gone, dry the sanded area thoroughly and inspect it for any signs of the scratch. If you have clearcoat paint and the sanding water shows any sign of color, you’ll have to respray the clear. If you have conventional (nonclearcoat) enamel or lacquer, the water will show plenty of color. Once the scratch is gone — and you haven’t sanded down to the next layer — buff the area with rubbing compound. A power buffer works fast, but you can do a fine job on smaller areas with no more than a terry cloth washcloth and a bottle of compound. Buff in a circular motion, and lift up the haze with a terry cloth towel.

When the sandpaper scratches are gone, use a soft cloth to remove any of the relatively coarse compound. You may need to wash the area with water. Replace the rubbing-compound pad on the machine with a foam polishing-compound pad, and buff the entire area with very fine compound or swirl mark eliminator. Once the polishing is done, inspect the area, then seal the paint with car wax.



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