I have been asked to quote a spray paint graffiti removal job today. Approx 50m2 of red brick wall needs to be cleaned. Some of the graffiti has been on for over a year other bits about 2 weeks. Does anyone have any recommendations as to what chemical/Brand to use for quick and efficient removal? The stuff I used on the last similar job I did took a lot more time than a lot of the videos show on the internet. I really want to impress on this job as the manager of the building admitted there will probably be some back in a few days. Potential for some on going work until the "artist" who is known to police either gets caught or gives up. Any help appreciated. Also those that have experience do you charge by the square meter or the job as a whole?