Q: We have a concrete tide gate that was recently hit by graffiti, covering much of the surface. We could paint over it, however, then we would have the ongoing maintenance of the paint. Can you recommend the best cleaning methods? If we sandblast it, will it harm the integrity of the concrete?
A: The Bureau of Justice Statistics estimates that 35% of the vandalism in the United States is graffiti and, according to PUBLIC WORKS magazine, each incidence of graffiti costs about $250 to remove. So you aren't alone, and there are various ways to respond, including sandblasting. You might start with simple high-pressure hot water or steam, which can sometimes be effective on latex paints. Moving up in cost, try some of the commercial graffiti removers, such as Elephant Snot or the products from Graffiti Removal Inc. (www.graffitiremovalinc.com). Sandblasting should be the last resort, although it won't significantly deteriorate the surface. Unlike flatwork that has a densified surface from finishing operations, the surface of concrete cast in forms is not of a higher quality than concrete in the middle of the wall and could be of slightly lower quality if the forms were stripped early and the surface was not cured properly. Another concern is that you will reduce the concrete cover over the reinforcing steel, even though sandblasting won't remove more than a few millimeters of concrete, which is not enough to make a difference with the cover. After you remove the graffiti, you might want to try one of the anti-graffiti coatings available that allows easy removal of new attacks.