Concrete is a mixture of gravel, sand, cement and water. When the water evaporates from this combination a very strong and durable solid remains. Concrete can withstand much wear and tear, but it is not impervious to stains. Acrylic paint can seem especially difficult to remove, but it is actually fairly easy to do so. Always begin with the easiest method and progress to other methods if the paint stains remain.
Blot up as much excess wet paint as possible with a rag.
Mix 2 tbsp. dish washing detergent into 1 gallon of warm water. Dip a stiff bristle scrub brush into the soapy solution and scrub the paint stains. Rinse off the area with water. Oftentimes, scrubbing is all that is needed to remove paint stains.
If scrubbing does not work, soak a rag in paint thinner and lay the rag on top of the paint stain for an hour or two to allow the paint to soften. Use a paint scraper to scrape softened paint off of the concrete surface. Rinse the area thoroughly with a hose to remove all traces of paint thinner.
If paint thinner does not work, use muriatic acid. Muriatic acid is a strong corrosive and requires the user to wear gloves, goggles and protective clothing. It is to be used only in a well-ventilated area or the user must wear a respirator. Mix muriatic acid according to package directions, usually a weak solution of one part acid to ten parts water is all that is necessary. Dip a stiff bristle scrub brush into the acid solution and apply to the paint stain. Scrub the stain until it disappears. Flush several times with water.