When paint gets onto concrete by accident, or as graffiti, it is difficult to remove because the concrete is so porous that the paint soaks down in.
We decided to test a few different removers.
Bio-Wash Masonry Strip works very well at removing oil, latex, and spray enamel paints.
De-Greaser from Stone Mason does an OK job with all three types of paint if you use a brush for oil and latex paints.
Graffiti Remover from Goof-Off does an OK job removing oil and latex paints, and a good job removing spray enamel.
It is far more effective to take the stripper off with a high pressure water spray as this forces the stuff out of the concrete pores far better than using a brush.