Removing paint from porous surfaces like wood and fabric can be a difficult endeavour because they tend to soak up paint which leads to strong adhesion. Like wood, brick and concrete are porous; however, because these two types of surfaces are so durable, they allow for much greater friction during the paint removal process, making them much easier to clean. Still, it is important to take care when you are removing paint drips and splatters from brick and concrete or you may scar the very surface you are trying to save.
Scrape away as much of the paint as possible from the brick or concrete surface using the metal putty knife. Be careful not to scrape too hard in the mortar between bricks as this may cause some of it to break loose.
Use a pressure washer to remove as much of the paint as possible. Begin the pressure washer on a low setting and then gradually increase pressure. Stand 3 feet from the brick or concrete surface initially and then slowly decrease the space between the two. Maintain at least a 1-foot space between the tip of the washer and the brick or concrete surface to avoid unintentional damage. Move to the next step only if any paint remains on the surface.
Dampen a rag with white spirit and then wipe down the area with paint on it. Allow the white spirit to soak in for one full minute.
Scrape loose the paint using a wire brush. Scrape in a circular, clockwise motion.
Wipe away the loosened paint using the damp rag.
If you are trying to remove latex paint from brick or concrete, you may be surprised how effective the pressure washer can be. Often, a metal putty knife and the concentrated stream of a pressure washer is all that is needed to remove latex paint from most hard surfaces. If you would like to strip a painted brick or concrete surface to prepare it for a fresh coat of paint, apply paint thinner to the surface using an oil-based paintbrush. Allow the thinner to sit for three full minutes, and then scrape away all of the paint using a metal putty knife. Only use this method if you plan to paint over the surface and aren't worried about scarring it.
Pressure washers are powerful enough to damage concrete and brick. Never bring the tip closer than 1 foot to the surface you are trying to clean.