Full list of Nuggets
How can you remove graffiti from concrete?
Paints and markers are made from a variety of binders, pigments and dyes. Some form a surface skin, others are absorbed into porous materials. This makes them quite difficult to remove without damage to the concrete surface.
As paints and markers are increasingly solvent-free, first try water-lances and brushing with liquid detergent. However, chemical cleaners will be needed in many cases.
Water based gel or paste paint removers to BS 3761 are preferred as they hold the active agent in contact with the graffiti for a long period while resisting absorption into the wall. Plastic sheeting draped over the treated wall will extend the time of action, especially when there are good drying conditions. The paint remover is then washed-off with a pressure that does not damage the wall surface. Hot water can be more effective than cold. A neutralising agent, if appropriate, can be applied and rinsed until a neutral test is obtained.
Residual ghosting may remain which can be removed by air abrasion. This should only be used if the finished produced is acceptable.
Acknowledgement: The Concrete Society
Other references:BRE Good Repair Guide 27 Part 1 Cleaning external walls of buildings: cleaning methods
BRE Good Repair Guide 27 Part 2 Cleaning external walls of buildings: removing dirts and stains
Concrete Bookshop - Members receive 40% discount on Concrete Society publications