A smooth concrete floor must be roughened before paint will stick to it. You roughen such a floor by etching it with muriatic acid. Muriatic acid acts like liquid sandpaper by roughening the surface of the concrete. It also reduces the surface alkalinity of the concrete that can cause some paints to adhere poorly. Muriatic acid is diluted hydrochloric acid; it should be handled with extreme care. Other, safer products are available for etching concrete and should be used for any indoor applications.
Clean the concrete surface. Remove any dirt, oil or other contaminants.
Dampen the surface to be etched with clean water. The concrete should be uniformly wet. Avoid puddles or dry spots. These will affect the etching process. The concrete must remain damp during the etching process. To prevent dry spots, divide a large surface into smaller areas and etch them one at a time.
Put on protective gear. Muriatic acid can cause severe damage to your eyes, skin, nose, throat and lungs. Do not open the container before putting on your safety gear.
Mix an acid solution by pouring 1 part acid into 10 parts water. Put the required amount of water into a plastic bucket, then add the acid to the water. Do not put acid in the bucket and add water. This reverse order is dangerous and can cause the acid to bubble violently.
Pour the mixture into a plastic garden watering can.
Sprinkle the mixture evenly across the surface of the prepared concrete. Allow the mixture to sit on the concrete until it stops bubbling.
Rinse the concrete thoroughly with water.