Stained concrete floors are attractive, colorful and durable. Though concrete floors are hard and tough, they are still susceptible to damage, just like any other kind of flooring. Improper care, accidents and even normal use can scratch the floor, and the best way to repair the damage depends upon how severe it is.
Your concrete floor can develop scratches from ordinary use, even if you care for it well. Stained concrete floors must be sealed to protect the floor, and often have a finish, like a wax, over the sealer. You can restore scratches in this finish by applying a new finish. For a floor in a home that gets a normal amount of use, you should reapply a finish about once a year. Sprinkle a floor finish across your floor, then spread it with either a lambswool applicator or a loop end mop. While you could simply reapply the finish to areas that are scratched, this may cause an uneven level of gloss on the floor.
If the floor doesn't have a finish, then you may have scratches in the sealer. You can reapply sealer, as well. For a quick fix on a small or confined area, wipe down the area with a solvent, then apply a light coating of new sealer. There are several usable solvents, but xylene or xylol is the one most often used for this. This product is highly flammable and toxic, so take all necessary precautions, and be sure that all of your tools are solvent-resistant.
If there are scratches in the concrete itself, then your only effective solution is to regrind and polish the concrete with a concrete polishing machine. These machines use wheels embedded with a hard grinding material to wear down the concrete in thin layers and both smooth and polish the surface. The results of this may vary depending on the extent of the damage, your concrete and what kind of stain you used; if the stain doesn't penetrate very deeply into the concrete and you need to remove a lot of material to take away the scratches, you may wind up grinding away the color. While you can do this yourself with rented equipment, it's best to hire a professional.
The most important way to prevent further problems or to protect your work after repair is to keep your floor clean. Weekly dust mopping with a microfiber dust mop is ideal and will remove most dirt particles. A buildup of dirt can act as an abrasive to your floor and will scratch it. Mop with cool water and a mild, pH-neutral cleaner when the regular dry mopping doesn't help any more; this will bring back the appearance of a dull or dirty floor. Adding pads to the legs of your furniture will also protect the floor.