When your concrete or wood sub floor is uneven, then floor leveling is very important before you install any type of finish flooring. There are self-leveling compounds available at home-improvement centers that are easy to use and that dry quickly.
The surface must be free of dirt and grime. Use a professional-quality shop vac and clean the floor carefully. Then wash the floor with a mild detergent. When dry, the entire floor must be primed with self-leveling primer. Take a four-foot level and go over the whole floor, marking the low spots with a carpenter’s pencil.
Mix the compound following the instructions with cold water in a five-gallon bucket. Use a power drill with a mixing attachment and mix thoroughly. Scrape the sides often to ensure it is all blended. You will need to work quickly as the compound will set up in less than 30 minutes. You might have to do the leveling in stages if you have a lot of low spots. Pour the leveling compound onto the areas you marked. Using a trowel smooth out and feather the edges. You will be able to walk on the floor after 4 hours, and be able to install your new floor after 24 hours.