Use a 15-degree nozzle with the machine set to 2 500 to 3 000 pounds of pressure per square inch. Hold the wand at an angle with the nozzle about 12 to 18 inches from the surface. Keep it moving to avoid digging a hole or valley in the concrete.
f the paint still sticks, invest in a chemical stripper. There are three main types: solvent-based strippers, which often contain methylene chloride or N-Methylpyrrolidone (NMP); caustic strippers, which contain lye, as either potassium hydroxide or sodium hydroxide; and biochemical strippers, which contain plant-based ingredients such as pine oil, corn sugars, citric acid and soy oil.
Solvent-based strippers work fastest and are favoured by many pros, but they are generally considered most dangerous. Biochemical strippers work slowest but are considered safest.
Whichever type you choose, read the label completely to find out what protective gear you need, the temperature range at which the product will work and the recommended application details. Most strippers need to be kept damp to work, which can be a challenge outdoors. So avoid doing this job on a hot, windy day, especially when the walkway is in direct sun. Cover nearby plants to protect them.
With many strippers, the paint bubbles up when it is ready to be removed. Scrape off as much as you can with a plastic putty knife, and scrub the remains with a fibre brush or plastic scrub pad. Then neutralize (if the label on the stripper says this is required) and wash thoroughly.