Masonry surfaces are rougher and more porous than wood or metal, and require slightly different painting techniques. The first thing to do is make sure the surface is ready for painting. Concrete needs exposure to air in order to cure before you seal it with paint. Allow at least several months for new concrete, and at least a month for repairs or patches. You can choose either regular exterior latex or special concrete paints, depending on your needs. Some surfaces may require primers or sealers before painting. Check with a paint specialist to determine your individual needs. Keep in mind that concrete will soak up more paint than other materials, so adjust the amount you buy accordingly. Old paint can be scraped off with a wire brush. For large areas, it's probably better to rent a sandblaster to use on anything other than brick. Don't use your regular brush on concrete; the rough surface can ruin it. Get a special brush with heavy bristles that can stand up to the abrasive surface. If you use a roller, make sure it has a medium nap for fairly smooth concrete, and an extra-long one for rough surfaces like stucco. Regular household spray guns aren't generally up to the task of concrete painting; consider renting a professional rig for big jobs.