Even garage floors with the best finish and best protection suffer damage and distortion from regular wear and tear and will have to be fixed up at some point. However, this is a task that can easily be taken on by the average do-it-yourselfer. There are several products available that make the job a snap depending on the type of fix your garage floor needs.
Cleaning the Floor
Regardless of the techniques or products that you're using, it's essential that the floor is swept clean and then vacuumed of any loose debris before tackling any repair. It's especially important to clean the damaged area. Loose debris from cracks and holes and dust will prevent the repair material from properly bonding to the concrete floor.
If you have paint or another finish on top of the concrete flooring, it is best to remove it around the repair spot for the same reason you need to clean dirt and debris. Your repair won't last if it bonds to the finish instead of the concrete itself. Paint can be reapplied when the damage is fixed. Sand the edges of the paint around the patch to get a better blend when you do paint over it.
An epoxy-based filler would be the product of choice to repair noticeable cracks in the concrete floor. These products are usually applied with a caulking gun and are ideal for cracks since they can expand and contract to compensate for the expansion and contraction of the concrete.
Filling Pits and Gouges
For pit marks and other dings and chips, a concrete filler is the best choice. Simply follow the mixing instructions from the manufacturer and apply the material with a flooring trowel over the affected area. Make sure you follow the recommendations of the manufacturer regarding the drying time and temperature for their specific products. Drying it too fast can cause cracking.
Leveling the Floor
If there is a depression in the floor, or if the floor slopes improperly, a self-leveling compound will correct this. Mix the compound as directed and spread it across the entire floor. Gravity will make it settle and dry with a perfectly level surface. Be sure you check it afterward with a level just in case.
This is the only case in which you might need to remove all of the existing finish from your garage floor. Unless there is a distinct area where the floor is improperly sloping or depressed, you will want to err always on the side of caution and remove all finish to make sure the compound contacts and bonds with the concrete.
When you're finished with the repair, be sure you've allowed enough dry time before reapplying your floor finish, if needed.