Unless you want “the word” to spread, remove graffiti as soon as possible. That way, you not only prevent it from soaking into porous surfaces but also discourage other graffiti vandals. A wall with graffiti often attracts more people to put graffiti on it.
Since graffiti is usually in the form of paint, the most common approach is to use a chemical paint remover or solvent. Most of these also lift marks made by felt tip pens, lipstick, and other substances. To use methylene chloride, a strong but common solvent, carefully brush it on, wait two minutes and rinse with water while continuing to brush. Because of concerns that methylene chloride may be carcinogenic, D & A Lawrence Ltd prefers alkaline pastes that contain a caustic, such as potassium hydroxide or sodium hydroxide. Rub the paste on and let it sit for 10 to 15 minutes until it bubbles up; wipe or scrub it off; then rinse the surface with water and apply a neutraliser. Repeat two or three times if one application does not remove the graffiti.
Two other methods of removing graffiti are water blasting and sandblasting, both of which work better on brick, stone and concrete than on wood. Only of the finest-grade sandblasters work on metal without damaging the surface.
Speed tips: if you anticipate a graffiti hit on a particular surface apply an anti-graffiti coating or sealer. As a preventative measure, this will save you cleaning time in the future, especially when it comes to porous surfaces, like brick and concrete, and painted surfaces that can be damaged by graffiti-removing chemicals. Among the best coatings are alphatic urethanes, which do not yellow and resist abrasion and paint solvents used to remove paint. There are other coatings, like acrylics and epoxies, but acrylics dissolve when paint solvents are applied to graffiti and epoxies tend to yellow and discolour.
If you can find the paint that matches, painting over graffiti is generally the cheapest and easiest ways to deal with it.
Always wear rubber gloves and long sleeves when working with paint-removing chemicals. If you’ll be scrubbing the chemicals with a brush – or if you are sandblasting or using a pressure steamer – Wear protective goggles. Do not inhale the fumes of toxic chemicals. Always read product labels for the proper use and safety instructions.