This is what you need to do:
Scrub your concrete floor with a coarse nylon or wire brush. This will help remove any chipping or peeling paint that may be ready to come off. Be careful to go over every inch of your floor thoroughly to get every flake of loose paint up. After you have painted your floor, even once small chips can turn into a huge mess. After that is done, your next step is to scrub the concrete surface with soap and water. This will remove any dirt and dust particles that will prevent the paint and primer from adhering correctly to the floor. Now that you have washed and cleaned the floor tape off any areas that you do not want to get paint on with plastic sheeting or a canvas drop cloth. Secure it to the edges of the wall with blue painters tape for easy removal.
Now you’re ready to apply your concrete primer in a thin layer across the floor. A 3/8’’. rough nap paint roller works the best for application in large areas. When you are finished, let the primer dry until it's smooth and dry to the touch. Next paint your concrete floor with concrete floor paint also known as porch and floor paint. It's important that you purchase paint specifically for concrete floors as regular house paint will not suffice. Concrete floor paint is mixed with special additives to add durability for foot traffic. This paint can be purchased anywhere that regular paint is sold and can be mixed to the same colors. You can also use a 3/8’’ nap roller for applying the finished coat on your concrete floor. Avoid getting any dirt and debris on the roller. If you should do so, remove the dirt prior to continuing painting or replace the roller.
After the first coat has dried, applying a second coat is optional. Although another coat will add durability and extended the life of your concrete floor paint, it's usually not necessary with this type of paint.