Uneven exterior concrete slabs should be repaired for reasons of both convenience and safety. An even concrete slab is very important if you plan to build anything on your slab or lay down any type of outdoor tile. You can purchase concrete leveling compounds at home improvement retailers to level out the floor. Placing the compound on top of the existing concrete will allow you to make repairs to the low points that may cause problems.
Sweep the concrete area with a broom to remove any dirt from the slab. You will need a clean area to work with when you repair the concrete. Use a garden hose and water or a pressure washer to further clean off the slab. The pressure washer can apply much more force to the concrete material to remove hardened dirt. Allow the concrete about 30 minutes to dry.
Pour about 1/2 gallon of latex primer in a new or clean paint tray. Soak a clean brush roller into the latex primer. Apply a coating of the primer to the concrete slab. Let the latex dry for about 12 hours.
Find the lower, uneven spots in the slab that require repair. Pick out these spots specifically so that you don't wind up spending money on repairing the entire slab if it is not necessary. Place a 2-inch by 4-inch board onto the concrete and repair the areas were the board does not lay flat.
Pour the bag of leveling compound into a bucket. Add the proper amount of water to the bucket according to the leveling compound's manufacturer and mix the contents together using a mixing stick. Continue mixing together the water and compound until there are no more lumps.
Apply a coating of the compound to the identified low areas on the concrete slab, smoothing it out with a trowel. Work at a rapid pace since the leveling compound will dry in less than 1 hour after being mixed with water. Finish coating the slab as needed with the compound mixture. Allow the area at least 24 hours to completely dry before using the slab.